# Rambda
`Rambda` is smaller and faster alternative to the popular functional programming library **Ramda**. - [Documentation](https://selfrefactor.github.io/rambda/#/)
[](https://circleci.com/gh/selfrefactor/rambda/tree/master)[](https://codecov.io/gh/selfrefactor/rambda)[](https://packagephobia.com/result?p=rambda)[](https://nest.land/package/rambda)[](https://github.com/selfrefactor/rambda/pulls)
## ❯ Example use
```javascriptimport { compose, map, filter } from 'rambda'
const result = compose( map(x => x * 2), filter(x => x > 2))([1, 2, 3, 4])// => [6, 8]```
You can test this example in <a href="https://rambda.now.sh?const%20result%20%3D%20R.compose(%0A%20%20R.map(x%20%3D%3E%20x%20*%202)%2C%0A%20%20R.filter(x%20%3D%3E%20x%20%3E%202)%0A)(%5B1%2C%202%2C%203%2C%204%5D)%0A%0A%2F%2F%20%3D%3E%20%5B6%2C%208%5D">Rambda's REPL</a>
* [Differences between Rambda and Ramda](#differences-between-rambda-and-ramda)* [API](#api)* [Changelog](#-changelog)
[](#-example-use)
## ❯ Rambda's advantages
### TypeScript included
TypeScript definitions are included in the library, in comparison to **Ramda**, where you need to additionally install `@types/ramda`.
Still, you need to be aware that functional programming features in `TypeScript` are in development, which means that using **R.compose/R.pipe** can be problematic.
Important - Rambda version `7.1.0`(or higher) requires TypeScript version `4.3.3`(or higher).
### Understandable source code due to little usage of internals
`Ramda` uses a lot of internals, which hides a lot of logic. Reading the full source code of a method can be challenging.
### Better VSCode experience
If the project is written in Javascript, then `go to source definition` action will lead you to actual implementation of the method.
### Immutable TS definitions
You can use immutable version of Rambda definitions, which is linted with ESLint `functional/prefer-readonly-type` plugin.
```import {add} from 'rambda/immutable'```
### Deno support
Latest version of **Ramba** available for `Deno` users is 3 years old. This is not the case with **Rambda** as most of recent releases are available for `Deno` users.
Also, `Rambda` provides you with included TS definitions:
```// Deno extension(https://marketplace.visualstudio.com/items?itemName=denoland.vscode-deno)// is installed and initializedimport * as R from "https://deno.land/x/rambda/mod.ts";import * as Ramda from "https://deno.land/x/ramda/mod.ts";
R.add(1)('foo') // => will trigger warning in VSCode as it shouldRamda.add(1)('foo') // => will not trigger warning in VSCode```
### Dot notation for `R.path`, `R.paths`, `R.assocPath` and `R.lensPath`
Standard usage of `R.path` is `R.path(['a', 'b'], {a: {b: 1} })`.
In **Rambda** you have the choice to use dot notation(which is arguably more readable):
```R.path('a.b', {a: {b: 1} })```
### Comma notation for `R.pick` and `R.omit`
Similar to dot notation, but the separator is comma(`,`) instead of dot(`.`).
```R.pick('a,b', {a: 1 , b: 2, c: 3} })// No space allowed between properties```
### Speed
**Rambda** is generally more performant than `Ramda` as the [benchmarks](#-benchmarks) can prove that.
### Support
One of the main issues with `Ramda` is the slow process of releasing new versions. This is not the case with **Rambda** as releases are made on regular basis.
[](#-rambdas-advantages)
## ❯ Missing Ramda methods
<details><summary> Click to see the full list of 43 Ramda methods not implemented in Rambda and their status.</summary>- into- invert- invertObj- invoker- keysIn- lift- liftN- mapAccum- mapAccumRight- memoizeWith- mergeDeepWith- mergeDeepWithKey- mergeWithKey- nAry- nthArg- o- otherwise- pair- partialRight- pathSatisfies- pipeWith- project- promap- reduceRight- reduceWhile- reduced- remove- scan- sequence- splitWhenever- symmetricDifferenceWith- andThen- toPairsIn- unary- uncurryN- unfold- unionWith- until- useWith- valuesIn- xprod- thunkify- default Most of above methods are in progress to be added to **Rambda**. The following methods are not going to be added:- __ - placeholder method allows user to further customize the method call. While, it seems useful initially, the price is too high in terms of complexity for TypeScript definitions. If it is not easy exressable in TypeScript, it is not worth it as **Rambda** is a TypeScript first library.- construct - Using classes is not very functional programming oriented.- constructN - same as above- transduce - currently is out of focus- traverse - same as above</details>[](#-missing-ramda-methods) ## ❯ Install
- **yarn add rambda**- For UMD usage either use `./dist/rambda.umd.js` or the following CDN link:```https://unpkg.com/rambda@CURRENT_VERSION/dist/rambda.umd.js```
- with deno```import {add} from "https://deno.land/x/rambda/mod.ts";```
[](#-install)
## Differences between Rambda and Ramda
- Rambda's **type** detects async functions and unresolved `Promises`. The returned values are `'Async'` and `'Promise'`.- Rambda's **type** handles *NaN* input, in which case it returns `NaN`.- Rambda's **forEach** can iterate over objects not only arrays.- Rambda's **map**, **filter**, **partition** when they iterate over objects, they pass property and input object as predicate's argument.- Rambda's **filter** returns empty array with bad input(`null` or `undefined`), while Ramda throws.- Ramda's **clamp** work with strings, while Rambda's method work only with numbers.- Ramda's **indexOf/lastIndexOf** work with strings and lists, while Rambda's method work only with lists as iterable input.- Error handling, when wrong inputs are provided, may not be the same. This difference will be better documented once all brute force tests are completed.- TypeScript definitions between `rambda` and `@types/ramda` may vary.> If you need more **Ramda** methods in **Rambda**, you may either submit a `PR` or check the extended version of **Rambda** - [Rambdax](https://github.com/selfrefactor/rambdax). In case of the former, you may want to consult with [Rambda contribution guidelines.](CONTRIBUTING.md)[](#-differences-between-rambda-and-ramda)
## ❯ Benchmarks
<details><summary>Click to expand all benchmark results
There are methods which are benchmarked only with `Ramda` and `Rambda`(i.e. no `Lodash`).
Note that some of these methods, are called with and without curring. This is done in order to give more detailed performance feedback.
The benchmarks results are produced from latest versions of *Rambda*, *Lodash*(4.17.21) and *Ramda*(0.29.1).
</summary>method | Rambda | Ramda | Lodash--- |--- | --- | --- *add* | 🚀 Fastest | 21.52% slower | 82.15% slower *adjust* | 8.48% slower | 🚀 Fastest | 🔳 *all* | 🚀 Fastest | 7.18% slower | 🔳 *allPass* | 🚀 Fastest | 88.25% slower | 🔳 *allPass* | 🚀 Fastest | 98.56% slower | 🔳 *and* | 🚀 Fastest | 89.09% slower | 🔳 *any* | 🚀 Fastest | 92.87% slower | 45.82% slower *anyPass* | 🚀 Fastest | 98.25% slower | 🔳 *append* | 🚀 Fastest | 2.07% slower | 🔳 *applySpec* | 🚀 Fastest | 80.43% slower | 🔳 *assoc* | 72.32% slower | 60.08% slower | 🚀 Fastest *clone* | 🚀 Fastest | 91.86% slower | 86.48% slower *compose* | 6.07% slower | 16.89% slower | 🚀 Fastest *converge* | 78.63% slower | 🚀 Fastest | 🔳 *curry* | 🚀 Fastest | 28.86% slower | 🔳 *curryN* | 🚀 Fastest | 41.05% slower | 🔳 *defaultTo* | 🚀 Fastest | 48.91% slower | 🔳 *drop* | 🚀 Fastest | 82.35% slower | 🔳 *dropLast* | 🚀 Fastest | 86.74% slower | 🔳 *equals* | 58.37% slower | 96.73% slower | 🚀 Fastest *filter* | 6.7% slower | 72.03% slower | 🚀 Fastest *find* | 🚀 Fastest | 85.14% slower | 42.65% slower *findIndex* | 🚀 Fastest | 86.48% slower | 72.27% slower *flatten* | 🚀 Fastest | 85.68% slower | 3.57% slower *ifElse* | 🚀 Fastest | 58.56% slower | 🔳 *includes* | 🚀 Fastest | 81.64% slower | 🔳 *indexOf* | 🚀 Fastest | 80.17% slower | 🔳 *indexOf* | 🚀 Fastest | 82.2% slower | 🔳 *init* | 🚀 Fastest | 92.24% slower | 13.3% slower *is* | 🚀 Fastest | 57.69% slower | 🔳 *isEmpty* | 🚀 Fastest | 97.14% slower | 54.99% slower *last* | 🚀 Fastest | 93.43% slower | 5.28% slower *lastIndexOf* | 🚀 Fastest | 85.19% slower | 🔳 *map* | 🚀 Fastest | 86.6% slower | 11.73% slower *match* | 🚀 Fastest | 44.83% slower | 🔳 *merge* | 🚀 Fastest | 12.21% slower | 55.76% slower *none* | 🚀 Fastest | 96.48% slower | 🔳 *objOf* | 🚀 Fastest | 38.05% slower | 🔳 *omit* | 🚀 Fastest | 69.95% slower | 97.34% slower *over* | 🚀 Fastest | 56.23% slower | 🔳 *path* | 37.81% slower | 77.81% slower | 🚀 Fastest *pick* | 🚀 Fastest | 19.07% slower | 80.2% slower *pipe* | 🚀 Fastest | 0.11% slower | 🔳 *prop* | 🚀 Fastest | 87.95% slower | 🔳 *propEq* | 🚀 Fastest | 91.92% slower | 🔳 *range* | 🚀 Fastest | 61.8% slower | 57.44% slower *reduce* | 60.48% slower | 77.1% slower | 🚀 Fastest *repeat* | 48.57% slower | 68.98% slower | 🚀 Fastest *replace* | 33.45% slower | 33.99% slower | 🚀 Fastest *set* | 🚀 Fastest | 50.35% slower | 🔳 *sort* | 🚀 Fastest | 40.23% slower | 🔳 *sortBy* | 🚀 Fastest | 25.29% slower | 56.88% slower *split* | 🚀 Fastest | 55.37% slower | 17.64% slower *splitEvery* | 🚀 Fastest | 71.98% slower | 🔳 *take* | 🚀 Fastest | 91.96% slower | 4.72% slower *takeLast* | 🚀 Fastest | 93.39% slower | 19.22% slower *test* | 🚀 Fastest | 82.34% slower | 🔳 *type* | 🚀 Fastest | 48.6% slower | 🔳 *uniq* | 🚀 Fastest | 84.9% slower | 🔳 *uniqBy* | 51.93% slower | 🚀 Fastest | 🔳 *uniqWith* | 8.29% slower | 🚀 Fastest | 🔳 *uniqWith* | 14.23% slower | 🚀 Fastest | 🔳 *update* | 🚀 Fastest | 52.35% slower | 🔳 *view* | 🚀 Fastest | 76.15% slower | 🔳</details>[](#-benchmarks)
## ❯ Used by
- [ESLint plugin Mocha](https://www.npmjs.com/package/eslint-plugin-mocha)- [WatermelonDB](https://github.com/Nozbe/WatermelonDB)- [Walmart Canada](https://www.walmart.ca) reported by [w-b-dev](https://github.com/w-b-dev) - [VSCode Slack integration](https://github.com/verydanny/vcslack)- [Webpack PostCSS](https://github.com/sectsect/webpack-postcss)- [MobX-State-Tree decorators](https://github.com/farwayer/mst-decorators)- [Rewrite of the Betaflight configurator](https://github.com/freshollie/fresh-configurator)- [MineFlayer plugin](https://github.com/G07cha/MineflayerArmorManager)[](#-used-by)
## API
### add
It adds `a` and `b`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.add(2%2C%203)%20%2F%2F%20%3D%3E%20%205">Try this <strong>R.add</strong> example in Rambda REPL</a>[](#add)
### addIndex
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.addIndex(R.map)((val%2C%20idx)%20%3D%3E%20val%20%2B%20idx%20%2B%201%2C%20%5B1%2C%202%2C%203%5D)%0A%2F%2F%20%3D%3E%20%5B2%2C%204%2C%206%5D">Try this <strong>R.addIndex</strong> example in Rambda REPL</a>[](#addIndex)
### addIndexRight
Same as `R.addIndex`, but it will passed indexes are decreasing, instead of increasing.
[](#addIndexRight)
### adjust
```typescript
adjust<T>(index: number, replaceFn: (x: T) => T, list: T[]): T[]```
It replaces `index` in array `list` with the result of `replaceFn(list[i])`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.adjust(%0A%20%200%2C%0A%20%20a%20%3D%3E%20a%20%2B%201%2C%0A%20%20%5B0%2C%20100%5D%0A)%20%2F%2F%20%3D%3E%20%5B1%2C%20100%5D">Try this <strong>R.adjust</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptadjust<T>(index: number, replaceFn: (x: T) => T, list: T[]): T[];adjust<T>(index: number, replaceFn: (x: T) => T): (list: T[]) => T[];```
</details><details><summary><strong>R.adjust</strong> source</summary>```javascriptimport { cloneList } from './_internals/cloneList.js'import { curry } from './curry.js'
function adjustFn( index, replaceFn, list){ const actualIndex = index < 0 ? list.length + index : index if (index >= list.length || actualIndex < 0) return list const clone = cloneList(list) clone[ actualIndex ] = replaceFn(clone[ actualIndex ]) return clone}
export const adjust = curry(adjustFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { add } from './add.js'import { adjust } from './adjust.js'import { pipe } from './pipe.js'
const list = [ 0, 1, 2 ]const expected = [ 0, 11, 2 ]
test('happy', () => {})
test('happy', () => { expect(adjust( 1, add(10), list )).toEqual(expected)})
test('with curring type 1 1 1', () => { expect(adjust(1)(add(10))(list)).toEqual(expected)})
test('with curring type 1 2', () => { expect(adjust(1)(add(10), list)).toEqual(expected)})
test('with curring type 2 1', () => { expect(adjust(1, add(10))(list)).toEqual(expected)})
test('with negative index', () => { expect(adjust( -2, add(10), list )).toEqual(expected)})
test('when index is out of bounds', () => { const list = [ 0, 1, 2, 3 ] expect(adjust( 4, add(1), list )).toEqual(list) expect(adjust( -5, add(1), list )).toEqual(list)})```
</details>[](#adjust)
### all
```typescript
all<T>(predicate: (x: T) => boolean, list: T[]): boolean```
It returns `true`, if all members of array `list` returns `true`, when applied as argument to `predicate` function.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%200%2C%201%2C%202%2C%203%2C%204%20%5D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3E%20-1%0A%0Aconst%20result%20%3D%20R.all(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.all</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptall<T>(predicate: (x: T) => boolean, list: T[]): boolean;all<T>(predicate: (x: T) => boolean): (list: T[]) => boolean;```
</details><details><summary><strong>R.all</strong> source</summary>```javascriptexport function all(predicate, list){ if (arguments.length === 1) return _list => all(predicate, _list) for (let i = 0; i < list.length; i++){ if (!predicate(list[ i ])) return false } return true}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { all } from './all.js'
const list = [ 0, 1, 2, 3, 4 ]
test('when true', () => { const fn = x => x > -1 expect(all(fn)(list)).toBeTrue()})
test('when false', () => { const fn = x => x > 2 expect(all(fn, list)).toBeFalse()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {all} from 'rambda'
describe('all', () => { it('happy', () => { const result = all( x => { x // $ExpectType number return x > 0 }, [1, 2, 3] ) result // $ExpectType boolean }) it('curried needs a type', () => { const result = all<number>(x => { x // $ExpectType number return x > 0 })([1, 2, 3]) result // $ExpectType boolean })})```
</details>[](#all)
### allPass
```typescript
allPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean```
It returns `true`, if all functions of `predicates` return `true`, when `input` is their argument.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20input%20%3D%20%7B%0A%20%20a%20%3A%201%2C%0A%20%20b%20%3A%202%2C%0A%7D%0Aconst%20predicates%20%3D%20%5B%0A%20%20x%20%3D%3E%20x.a%20%3D%3D%3D%201%2C%0A%20%20x%20%3D%3E%20x.b%20%3D%3D%3D%202%2C%0A%5D%0Aconst%20result%20%3D%20R.allPass(predicates)(input)%20%2F%2F%20%3D%3E%20true">Try this <strong>R.allPass</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptallPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean;allPass<T>(predicates: ((...inputs: T[]) => boolean)[]): (...inputs: T[]) => boolean;```
</details><details><summary><strong>R.allPass</strong> source</summary>```javascriptexport function allPass(predicates){ return (...input) => { let counter = 0 while (counter < predicates.length){ if (!predicates[ counter ](...input)){ return false } counter++ } return true }}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { allPass } from './allPass.js'
test('happy', () => { const rules = [ x => typeof x === 'number', x => x > 10, x => x * 7 < 100 ] expect(allPass(rules)(11)).toBeTrue() expect(allPass(rules)(undefined)).toBeFalse()})
test('when returns true', () => { const conditionArr = [ val => val.a === 1, val => val.b === 2 ] expect(allPass(conditionArr)({ a : 1, b : 2, })).toBeTrue()})
test('when returns false', () => { const conditionArr = [ val => val.a === 1, val => val.b === 3 ] expect(allPass(conditionArr)({ a : 1, b : 2, })).toBeFalse()})
test('works with multiple inputs', () => { const fn = function ( w, x, y, z ){ return w + x === y + z } expect(allPass([ fn ])( 3, 3, 3, 3 )).toBeTrue()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {allPass, filter} from 'rambda'
describe('allPass', () => { it('happy', () => { const x = allPass<number>([ y => { y // $ExpectType number return typeof y === 'number' }, y => { return y > 0 }, ])(11) x // $ExpectType boolean }) it('issue #642', () => { const isGreater = (num: number) => num > 5 const pred = allPass([isGreater]) const xs = [0, 1, 2, 3] const filtered1 = filter(pred)(xs) filtered1 // $ExpectType number[] const filtered2 = xs.filter(pred) filtered2 // $ExpectType number[] }) it('issue #604', () => { const plusEq = function(w: number, x: number, y: number, z: number) { return w + x === y + z } const result = allPass([plusEq])(3, 3, 3, 3) result // $ExpectType boolean })})```
</details>[](#allPass)
### always
It returns function that always returns `x`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20R.always(7)%0A%0Aconst%20result%20%3D%20fn()%0A%2F%2F%20%3D%3E%207">Try this <strong>R.always</strong> example in Rambda REPL</a>[](#always)
### and
Logical AND
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.and(true%2C%20true)%3B%20%2F%2F%20%3D%3E%20true%0AR.and(false%2C%20true)%3B%20%2F%2F%20%3D%3E%20false%0Aconst%20result%20%3D%20R.and(true%2C%20'foo')%3B%20%2F%2F%20%3D%3E%20'foo'">Try this <strong>R.and</strong> example in Rambda REPL</a>[](#and)
### any
```typescript
any<T>(predicate: (x: T) => boolean, list: T[]): boolean```
It returns `true`, if at least one member of `list` returns true, when passed to a `predicate` function.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20*%20x%20%3E%208%0Aconst%20result%20%3D%20R.any(fn%2C%20list)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.any</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptany<T>(predicate: (x: T) => boolean, list: T[]): boolean;any<T>(predicate: (x: T) => boolean): (list: T[]) => boolean;```
</details><details><summary><strong>R.any</strong> source</summary>```javascriptexport function any(predicate, list){ if (arguments.length === 1) return _list => any(predicate, _list) let counter = 0 while (counter < list.length){ if (predicate(list[ counter ], counter)){ return true } counter++ } return false}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { any } from './any.js'
const list = [ 1, 2, 3 ]
test('happy', () => { expect(any(x => x < 0, list)).toBeFalse()})
test('with curry', () => { expect(any(x => x > 2)(list)).toBeTrue()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {any} from 'rambda'
describe('R.any', () => { it('happy', () => { const result = any( x => { x // $ExpectType number return x > 2 }, [1, 2, 3] ) result // $ExpectType boolean }) it('when curried needs a type', () => { const result = any<number>(x => { x // $ExpectType number return x > 2 })([1, 2, 3]) result // $ExpectType boolean })})```
</details>[](#any)
### anyPass
```typescript
anyPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean```
It accepts list of `predicates` and returns a function. This function with its `input` will return `true`, if any of `predicates` returns `true` for this `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20isBig%20%3D%20x%20%3D%3E%20x%20%3E%2020%0Aconst%20isOdd%20%3D%20x%20%3D%3E%20x%20%25%202%20%3D%3D%3D%201%0Aconst%20input%20%3D%2011%0A%0Aconst%20fn%20%3D%20R.anyPass(%0A%20%20%5BisBig%2C%20isOdd%5D%0A)%0A%0Aconst%20result%20%3D%20fn(input)%20%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.anyPass</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptanyPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean;anyPass<T>(predicates: ((...inputs: T[]) => boolean)[]): (...inputs: T[]) => boolean;```
</details><details><summary><strong>R.anyPass</strong> source</summary>```javascriptexport function anyPass(predicates){ return (...input) => { let counter = 0 while (counter < predicates.length){ if (predicates[ counter ](...input)){ return true } counter++ } return false }}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { anyPass } from './anyPass.js'
test('happy', () => { const rules = [ x => typeof x === 'string', x => x > 10 ] const predicate = anyPass(rules) expect(predicate('foo')).toBeTrue() expect(predicate(6)).toBeFalse()})
test('happy', () => { const rules = [ x => typeof x === 'string', x => x > 10 ] expect(anyPass(rules)(11)).toBeTrue() expect(anyPass(rules)(undefined)).toBeFalse()})
const obj = { a : 1, b : 2,}
test('when returns true', () => { const conditionArr = [ val => val.a === 1, val => val.a === 2 ] expect(anyPass(conditionArr)(obj)).toBeTrue()})
test('when returns false + curry', () => { const conditionArr = [ val => val.a === 2, val => val.b === 3 ] expect(anyPass(conditionArr)(obj)).toBeFalse()})
test('with empty predicates list', () => { expect(anyPass([])(3)).toBeFalse()})
test('works with multiple inputs', () => { const fn = function ( w, x, y, z ){ console.log( w, x, y, z ) return w + x === y + z } expect(anyPass([ fn ])( 3, 3, 3, 3 )).toBeTrue()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {anyPass, filter} from 'rambda'
describe('anyPass', () => { it('happy', () => { const x = anyPass<number>([ y => { y // $ExpectType number return typeof y === 'number' }, y => { return y > 0 }, ])(11) x // $ExpectType boolean }) it('issue #604', () => { const plusEq = function(w: number, x: number, y: number, z: number) { return w + x === y + z } const result = anyPass([plusEq])(3, 3, 3, 3) result // $ExpectType boolean }) it('issue #642', () => { const isGreater = (num: number) => num > 5 const pred = anyPass([isGreater]) const xs = [0, 1, 2, 3] const filtered1 = filter(pred)(xs) filtered1 // $ExpectType number[] const filtered2 = xs.filter(pred) filtered2 // $ExpectType number[] }) it('functions as a type guard', () => { const isString = (x: unknown): x is string => typeof x === 'string' const isNumber = (x: unknown): x is number => typeof x === 'number' const isBoolean = (x: unknown): x is boolean => typeof x === 'boolean' const isStringNumberOrBoolean = anyPass([isString, isNumber, isBoolean]) isStringNumberOrBoolean // $ExpectType (input: unknown) => boolean const aValue: unknown = 1 if (isStringNumberOrBoolean(aValue)) { aValue // $ExpectType unknown } })})```
</details>[](#anyPass)
### ap
```typescript
ap<T, U>(fns: Array<(a: T) => U>[], vs: T[]): U[]```
It takes a list of functions and a list of values. Then it returns a list of values obtained by applying each function to each value.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.ap(%0A%20%20%5B%0A%20%20%20%20x%20%3D%3E%20x%20%2B%201%2C%0A%20%20%20%20x%20%3D%3E%20x%20%2B%202%2C%0A%20%20%5D%2C%0A%20%20%5B1%2C%202%2C%203%5D%0A)%0A%2F%2F%20%3D%3E%20%5B2%2C%203%2C%204%2C%203%2C%204%2C%205%5D">Try this <strong>R.ap</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptap<T, U>(fns: Array<(a: T) => U>[], vs: T[]): U[];ap<T, U>(fns: Array<(a: T) => U>): (vs: T[]) => U[];ap<R, A, B>(fn: (r: R, a: A) => B, fn1: (r: R) => A): (r: R) => B;```
</details><details><summary><strong>R.ap</strong> source</summary>```javascriptexport function ap(functions, input){ if (arguments.length === 1){ return _inputs => ap(functions, _inputs) } return functions.reduce((acc, fn) => [ ...acc, ...input.map(fn) ], [])}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { ap } from './ap.js'
function mult2(x){ return x * 2}function plus3(x){ return x + 3}
test('happy', () => { expect(ap([ mult2, plus3 ], [ 1, 2, 3 ])).toEqual([ 2, 4, 6, 4, 5, 6 ])})```
</details>[](#ap)
### aperture
```typescript
aperture<N extends number, T>(n: N, list: T[]): Array<Tuple<T, N>> | []```
It returns a new list, composed of consecutive `n`-tuples from a `list`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.aperture(2%2C%20%5B1%2C%202%2C%203%2C%204%5D)%0A%2F%2F%20%3D%3E%20%5B%5B1%2C%202%5D%2C%20%5B2%2C%203%5D%2C%20%5B3%2C%204%5D%5D">Try this <strong>R.aperture</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptaperture<N extends number, T>(n: N, list: T[]): Array<Tuple<T, N>> | [];aperture<N extends number>(n: N): <T>(list: T[]) => Array<Tuple<T, N>> | [];```
</details><details><summary><strong>R.aperture</strong> source</summary>```javascriptexport function aperture(step, list){ if (arguments.length === 1){ return _list => aperture(step, _list) } if (step > list.length) return [] let idx = 0 const limit = list.length - (step - 1) const acc = new Array(limit) while (idx < limit){ acc[ idx ] = list.slice(idx, idx + step) idx += 1 } return acc}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { aperture } from './aperture.js'
const list = [ 1, 2, 3, 4, 5, 6, 7 ]
test('happy', () => { expect(aperture(1, list)).toEqual([ [ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ] ]) expect(aperture(2, list)).toEqual([ [ 1, 2 ], [ 2, 3 ], [ 3, 4 ], [ 4, 5 ], [ 5, 6 ], [ 6, 7 ], ]) expect(aperture(3, list)).toEqual([ [ 1, 2, 3 ], [ 2, 3, 4 ], [ 3, 4, 5 ], [ 4, 5, 6 ], [ 5, 6, 7 ], ]) expect(aperture(8, list)).toEqual([])})```
</details>[](#aperture)
### append
```typescript
append<T>(xToAppend: T, iterable: T[]): T[]```
It adds element `x` at the end of `iterable`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20x%20%3D%20'foo'%0A%0Aconst%20result%20%3D%20R.append(x%2C%20%5B'bar'%2C%20'baz'%5D)%0A%2F%2F%20%3D%3E%20%5B'bar'%2C%20'baz'%2C%20'foo'%5D">Try this <strong>R.append</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptappend<T>(xToAppend: T, iterable: T[]): T[];append<T, U>(xToAppend: T, iterable: IsFirstSubtypeOfSecond<T, U>[]) : U[];append<T>(xToAppend: T): <U>(iterable: IsFirstSubtypeOfSecond<T, U>[]) => U[];append<T>(xToAppend: T): (iterable: T[]) => T[];```
</details><details><summary><strong>R.append</strong> source</summary>```javascriptimport { cloneList } from './_internals/cloneList.js'
export function append(x, input){ if (arguments.length === 1) return _input => append(x, _input) if (typeof input === 'string') return input.split('').concat(x) const clone = cloneList(input) clone.push(x) return clone}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { append } from './append.js'
test('happy', () => { expect(append('tests', [ 'write', 'more' ])).toEqual([ 'write', 'more', 'tests', ])})
test('append to empty array', () => { expect(append('tests')([])).toEqual([ 'tests' ])})
test('with strings', () => { expect(append('o', 'fo')).toEqual([ 'f', 'o', 'o' ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {append, prepend} from 'rambda'
const listOfNumbers = [1, 2, 3]const listOfNumbersAndStrings = [1, 'b', 3]
describe('R.append/R.prepend', () => { describe("with the same primitive type as the array's elements", () => { it('uncurried', () => { // @ts-expect-error append('d', listOfNumbers) // @ts-expect-error prepend('d', listOfNumbers) append(4, listOfNumbers) // $ExpectType number[] prepend(4, listOfNumbers) // $ExpectType number[] }) it('curried', () => { // @ts-expect-error append('d')(listOfNumbers) append(4)(listOfNumbers) // $ExpectType number[] prepend(4)(listOfNumbers) // $ExpectType number[] }) }) describe("with a subtype of the array's elements", () => { it('uncurried', () => { // @ts-expect-error append(true, listOfNumbersAndStrings) append(4, listOfNumbersAndStrings) // $ExpectType (string | number)[] prepend(4, listOfNumbersAndStrings) // $ExpectType (string | number)[] }) it('curried', () => { // @ts-expect-error append(true)(listOfNumbersAndStrings) append(4)(listOfNumbersAndStrings) // $ExpectType (string | number)[] prepend(4)(listOfNumbersAndStrings) // $ExpectType (string | number)[] }) }) describe("expanding the type of the array's elements", () => { it('uncurried', () => { // @ts-expect-error append('d', listOfNumbers) append<string | number>('d', listOfNumbers) // $ExpectType (string | number)[] prepend<string | number>('d', listOfNumbers) // $ExpectType (string | number)[] }) it('curried', () => { // @ts-expect-error append('d')(listOfNumbers) const appendD = append('d') appendD<string | number>(listOfNumbers) // $ExpectType (string | number)[] const prependD = prepend('d') prependD<string | number>(listOfNumbers) // $ExpectType (string | number)[] }) })})```
</details>[](#append)
### apply
```typescript
apply<T = any>(fn: (...args: any[]) => T, args: any[]): T```
It applies function `fn` to the list of arguments.
This is useful for creating a fixed-arity function from a variadic function. `fn` should be a bound function if context is significant.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.apply(Math.max%2C%20%5B42%2C%20-Infinity%2C%201337%5D)%0A%2F%2F%20%3D%3E%201337">Try this <strong>R.apply</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptapply<T = any>(fn: (...args: any[]) => T, args: any[]): T;apply<T = any>(fn: (...args: any[]) => T): (args: any[]) => T;```
</details><details><summary><strong>R.apply</strong> source</summary>```javascriptexport function apply(fn, args){ if (arguments.length === 1){ return _args => apply(fn, _args) } return fn.apply(this, args)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { apply } from './apply.js'import { bind } from './bind.js'import { identity } from './identity.js'
test('happy', () => { expect(apply(identity, [ 1, 2, 3 ])).toBe(1)})
test('applies function to argument list', () => { expect(apply(Math.max, [ 1, 2, 3, -99, 42, 6, 7 ])).toBe(42)})
test('provides no way to specify context', () => { const obj = { method (){ return this === obj }, } expect(apply(obj.method, [])).toBeFalse() expect(apply(bind(obj.method, obj), [])).toBeTrue()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {apply, identity} from 'rambda'
describe('R.apply', () => { it('happy', () => { const result = apply<number>(identity, [1, 2, 3]) result // $ExpectType number }) it('curried', () => { const fn = apply<number>(identity) const result = fn([1, 2, 3]) result // $ExpectType number })})```
</details>[](#apply)
### applySpec
```typescript
applySpec<Spec extends Record<string, AnyFunction>>( spec: Spec): ( ...args: Parameters<ValueOfRecord<Spec>>) => { [Key in keyof Spec]: ReturnType<Spec[Key]> }```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20R.applySpec(%7B%0A%20%20sum%3A%20R.add%2C%0A%20%20nested%3A%20%7B%20mul%3A%20R.multiply%20%7D%0A%7D)%0Aconst%20result%20%3D%20fn(2%2C%204)%20%0A%2F%2F%20%3D%3E%20%7B%20sum%3A%206%2C%20nested%3A%20%7B%20mul%3A%208%20%7D%20%7D">Try this <strong>R.applySpec</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptapplySpec<Spec extends Record<string, AnyFunction>>( spec: Spec): ( ...args: Parameters<ValueOfRecord<Spec>>) => { [Key in keyof Spec]: ReturnType<Spec[Key]> };applySpec<T>(spec: any): (...args: unknown[]) => T;```
</details><details><summary><strong>R.applySpec</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'
// recursively traverse the given spec object to find the highest arity functionexport function __findHighestArity(spec, max = 0){ for (const key in spec){ if (spec.hasOwnProperty(key) === false || key === 'constructor') continue if (typeof spec[ key ] === 'object'){ max = Math.max(max, __findHighestArity(spec[ key ])) } if (typeof spec[ key ] === 'function'){ max = Math.max(max, spec[ key ].length) } } return max}
function __filterUndefined(){ const defined = [] let i = 0 const l = arguments.length while (i < l){ if (typeof arguments[ i ] === 'undefined') break defined[ i ] = arguments[ i ] i++ } return defined}
function __applySpecWithArity( spec, arity, cache){ const remaining = arity - cache.length if (remaining === 1) return x => __applySpecWithArity( spec, arity, __filterUndefined(...cache, x) ) if (remaining === 2) return (x, y) => __applySpecWithArity( spec, arity, __filterUndefined( ...cache, x, y ) ) if (remaining === 3) return ( x, y, z ) => __applySpecWithArity( spec, arity, __filterUndefined( ...cache, x, y, z ) ) if (remaining === 4) return ( x, y, z, a ) => __applySpecWithArity( spec, arity, __filterUndefined( ...cache, x, y, z, a ) ) if (remaining > 4) return (...args) => __applySpecWithArity( spec, arity, __filterUndefined(...cache, ...args) ) // handle spec as Array if (isArray(spec)){ const ret = [] let i = 0 const l = spec.length for (; i < l; i++){ // handle recursive spec inside array if (typeof spec[ i ] === 'object' || isArray(spec[ i ])){ ret[ i ] = __applySpecWithArity( spec[ i ], arity, cache ) } // apply spec to the key if (typeof spec[ i ] === 'function'){ ret[ i ] = spec[ i ](...cache) } } return ret } // handle spec as Object const ret = {} // apply callbacks to each property in the spec object for (const key in spec){ if (spec.hasOwnProperty(key) === false || key === 'constructor') continue // apply the spec recursively if (typeof spec[ key ] === 'object'){ ret[ key ] = __applySpecWithArity( spec[ key ], arity, cache ) continue } // apply spec to the key if (typeof spec[ key ] === 'function'){ ret[ key ] = spec[ key ](...cache) } } return ret}
export function applySpec(spec, ...args){ // get the highest arity spec function, cache the result and pass to __applySpecWithArity const arity = __findHighestArity(spec) if (arity === 0){ return () => ({}) } const toReturn = __applySpecWithArity( spec, arity, args ) return toReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { applySpec as applySpecRamda, nAry } from 'ramda'
import { add, always, compose, dec, inc, map, path, prop, T,} from '../rambda.js'import { applySpec } from './applySpec.js'
test('different than Ramda when bad spec', () => { const result = applySpec({ sum : { a : 1 } })(1, 2) const ramdaResult = applySpecRamda({ sum : { a : 1 } })(1, 2) expect(result).toEqual({}) expect(ramdaResult).toEqual({ sum : { a : {} } })})
test('works with empty spec', () => { expect(applySpec({})()).toEqual({}) expect(applySpec([])(1, 2)).toEqual({}) expect(applySpec(null)(1, 2)).toEqual({})})
test('works with unary functions', () => { const result = applySpec({ v : inc, u : dec, })(1) const expected = { v : 2, u : 0, } expect(result).toEqual(expected)})
test('works with binary functions', () => { const result = applySpec({ sum : add })(1, 2) expect(result).toEqual({ sum : 3 })})
test('works with nested specs', () => { const result = applySpec({ unnested : always(0), nested : { sum : add }, })(1, 2) const expected = { unnested : 0, nested : { sum : 3 }, } expect(result).toEqual(expected)})
test('works with arrays of nested specs', () => { const result = applySpec({ unnested : always(0), nested : [ { sum : add } ], })(1, 2) expect(result).toEqual({ unnested : 0, nested : [ { sum : 3 } ], })})
test('works with arrays of spec objects', () => { const result = applySpec([ { sum : add } ])(1, 2) expect(result).toEqual([ { sum : 3 } ])})
test('works with arrays of functions', () => { const result = applySpec([ map(prop('a')), map(prop('b')) ])([ { a : 'a1', b : 'b1', }, { a : 'a2', b : 'b2', }, ]) const expected = [ [ 'a1', 'a2' ], [ 'b1', 'b2' ], ] expect(result).toEqual(expected)})
test('works with a spec defining a map key', () => { expect(applySpec({ map : prop('a') })({ a : 1 })).toEqual({ map : 1 })})
test('cannot retains the highest arity', () => { const f = applySpec({ f1 : nAry(2, T), f2 : nAry(5, T), }) const fRamda = applySpecRamda({ f1 : nAry(2, T), f2 : nAry(5, T), }) expect(f).toHaveLength(0) expect(fRamda).toHaveLength(5)})
test('returns a curried function', () => { expect(applySpec({ sum : add })(1)(2)).toEqual({ sum : 3 })})
// Additional tests// ============================================test('arity', () => { const spec = { one : x1 => x1, two : (x1, x2) => x1 + x2, three : ( x1, x2, x3 ) => x1 + x2 + x3, } expect(applySpec( spec, 1, 2, 3 )).toEqual({ one : 1, two : 3, three : 6, })})
test('arity over 5 arguments', () => { const spec = { one : x1 => x1, two : (x1, x2) => x1 + x2, three : ( x1, x2, x3 ) => x1 + x2 + x3, four : ( x1, x2, x3, x4 ) => x1 + x2 + x3 + x4, five : ( x1, x2, x3, x4, x5 ) => x1 + x2 + x3 + x4 + x5, } expect(applySpec( spec, 1, 2, 3, 4, 5 )).toEqual({ one : 1, two : 3, three : 6, four : 10, five : 15, })})
test('curried', () => { const spec = { one : x1 => x1, two : (x1, x2) => x1 + x2, three : ( x1, x2, x3 ) => x1 + x2 + x3, } expect(applySpec(spec)(1)(2)(3)).toEqual({ one : 1, two : 3, three : 6, })})
test('curried over 5 arguments', () => { const spec = { one : x1 => x1, two : (x1, x2) => x1 + x2, three : ( x1, x2, x3 ) => x1 + x2 + x3, four : ( x1, x2, x3, x4 ) => x1 + x2 + x3 + x4, five : ( x1, x2, x3, x4, x5 ) => x1 + x2 + x3 + x4 + x5, } expect(applySpec(spec)(1)(2)(3)(4)(5)).toEqual({ one : 1, two : 3, three : 6, four : 10, five : 15, })})
test('undefined property', () => { const spec = { prop : path([ 'property', 'doesnt', 'exist' ]) } expect(applySpec(spec, {})).toEqual({ prop : undefined })})
test('restructure json object', () => { const spec = { id : path('user.id'), name : path('user.firstname'), profile : path('user.profile'), doesntExist : path('user.profile.doesntExist'), info : { views : compose(inc, prop('views')) }, type : always('playa'), } const data = { user : { id : 1337, firstname : 'john', lastname : 'shaft', profile : 'shaft69', }, views : 42, } expect(applySpec(spec, data)).toEqual({ id : 1337, name : 'john', profile : 'shaft69', doesntExist : undefined, info : { views : 43 }, type : 'playa', })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {multiply, applySpec, inc, dec, add} from 'rambda'
describe('applySpec', () => { it('ramda 1', () => { const result = applySpec({ v: inc, u: dec, })(1) result // $ExpectType { v: number; u: number; } }) it('ramda 1', () => { interface Output { sum: number, multiplied: number, } const result = applySpec<Output>({ sum: add, multiplied: multiply, })(1, 2) result // $ExpectType Output })})```
</details>[](#applySpec)
### applyTo
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.applyTo(%0A%20%201%2C%0A%20%20x%20%3D%3E%20x%20%2B%201%0A)%0A%2F%2F%20%3D%3E%202">Try this <strong>R.applyTo</strong> example in Rambda REPL</a>[](#applyTo)
### ascend
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.sort(%0A%20%20R.ascend(x%20%3D%3E%20x)%2C%0A%20%20%5B2%2C%201%5D%0A)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.ascend</strong> example in Rambda REPL</a>[](#ascend)
### assoc
It makes a shallow clone of `obj` with setting or overriding the property `prop` with `newValue`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.assoc('c'%2C%203%2C%20%7Ba%3A%201%2C%20b%3A%202%7D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D">Try this <strong>R.assoc</strong> example in Rambda REPL</a>[](#assoc)
### assocPath
```typescript
assocPath<Output>(path: Path, newValue: any, obj: object): Output```
It makes a shallow clone of `obj` with setting or overriding with `newValue` the property found with `path`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20path%20%3D%20'b.c'%0Aconst%20newValue%20%3D%202%0Aconst%20obj%20%3D%20%7B%20a%3A%201%20%7D%0A%0Aconst%20result%20%3D%20R.assocPath(path%2C%20newValue%2C%20Record%3Cstring%2C%20unknown%3E)%0A%2F%2F%20%3D%3E%20%7B%20a%20%3A%201%2C%20b%20%3A%20%7B%20c%20%3A%202%20%7D%7D">Try this <strong>R.assocPath</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptassocPath<Output>(path: Path, newValue: any, obj: object): Output;assocPath<Output>(path: Path, newValue: any): (obj: object) => Output;assocPath<Output>(path: Path): (newValue: any) => (obj: object) => Output;```
</details><details><summary><strong>R.assocPath</strong> source</summary>```javascriptimport { cloneList } from './_internals/cloneList.js'import { createPath } from './_internals/createPath.js'import { isArray } from './_internals/isArray.js'import { isIndexInteger } from './_internals/isInteger.js'import { assocFn } from './assoc.js'import { curry } from './curry.js'
export function assocPathFn( path, newValue, input){ const pathArrValue = createPath(path) if (pathArrValue.length === 0) return newValue const index = pathArrValue[ 0 ] if (pathArrValue.length > 1){ const condition = typeof input !== 'object' || input === null || !input.hasOwnProperty(index) const nextInput = condition ? isIndexInteger(pathArrValue[ 1 ]) ? [] : {} : input[ index ] newValue = assocPathFn( Array.prototype.slice.call(pathArrValue, 1), newValue, nextInput ) } if (isIndexInteger(index) && isArray(input)){ const arr = cloneList(input) arr[ index ] = newValue return arr } return assocFn( index, newValue, input )}
export const assocPath = curry(assocPathFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { assocPathFn } from './assocPath.js'
test.only('happy', () => { const path = 'a.c.1' const input = { a : { b : 1, c : [ 1, 2 ], }, } assocPathFn( path, 3, input ) expect(input).toEqual({ a : { b : 1, c : [ 1, 2 ], }, })})
test('string can be used as path input', () => { const testObj = { a : [ { b : 1 }, { b : 2 } ], d : 3, } const result1 = assocPathFn( [ 'a', 0, 'b' ], 10, testObj ) const result2 = assocPathFn( 'a.0.b', 10, testObj ) const expected = { a : [ { b : 10 }, { b : 2 } ], d : 3, } expect(result1).toEqual(expected) expect(result2).toEqual(expected)})
test('difference with ramda - doesn\'t overwrite primitive values with keys in the path', () => { const obj = { a : 'str' } const result = assocPath( [ 'a', 'b' ], 42, obj ) expect(result).toEqual({ a : { 0 : 's', 1 : 't', 2 : 'r', b : 42, }, })})
test('bug', () => { /* https://github.com/selfrefactor/rambda/issues/524 */ const state = {} const withDateLike = assocPath( [ 'outerProp', '2020-03-10' ], { prop : 2 }, state ) const withNumber = assocPath( [ 'outerProp', '5' ], { prop : 2 }, state ) const withDateLikeExpected = { outerProp : { '2020-03-10' : { prop : 2 } } } const withNumberExpected = { outerProp : { 5 : { prop : 2 } } } expect(withDateLike).toEqual(withDateLikeExpected) expect(withNumber).toEqual(withNumberExpected)})
test('adds a key to an empty object', () => { expect(assocPath( [ 'a' ], 1, {} )).toEqual({ a : 1 })})
test('adds a key to a non-empty object', () => { expect(assocPath( 'b', 2, { a : 1 } )).toEqual({ a : 1, b : 2, })})
test('adds a nested key to a non-empty object', () => { expect(assocPath( 'b.c', 2, { a : 1 } )).toEqual({ a : 1, b : { c : 2 }, })})
test('adds a nested key to a nested non-empty object - curry case 1', () => { expect(assocPath('b.d', 3)({ a : 1, b : { c : 2 }, })).toEqual({ a : 1, b : { c : 2, d : 3, }, })})
test('adds a key to a non-empty object - curry case 1', () => { expect(assocPath('b', 2)({ a : 1 })).toEqual({ a : 1, b : 2, })})
test('adds a nested key to a non-empty object - curry case 1', () => { expect(assocPath('b.c', 2)({ a : 1 })).toEqual({ a : 1, b : { c : 2 }, })})
test('adds a key to a non-empty object - curry case 2', () => { expect(assocPath('b')(2, { a : 1 })).toEqual({ a : 1, b : 2, })})
test('adds a key to a non-empty object - curry case 3', () => { const result = assocPath('b')(2)({ a : 1 }) expect(result).toEqual({ a : 1, b : 2, })})
test('changes an existing key', () => { expect(assocPath( 'a', 2, { a : 1 } )).toEqual({ a : 2 })})
test('undefined is considered an empty object', () => { expect(assocPath( 'a', 1, undefined )).toEqual({ a : 1 })})
test('null is considered an empty object', () => { expect(assocPath( 'a', 1, null )).toEqual({ a : 1 })})
test('value can be null', () => { expect(assocPath( 'a', null, null )).toEqual({ a : null })})
test('value can be undefined', () => { expect(assocPath( 'a', undefined, null )).toEqual({ a : undefined })})
test('assignment is shallow', () => { expect(assocPath( 'a', { b : 2 }, { a : { c : 3 } } )).toEqual({ a : { b : 2 } })})
test('empty array as path', () => { const result = assocPath( [], 3, { a : 1, b : 2, } ) expect(result).toBe(3)})
test('happy', () => { const expected = { foo : { bar : { baz : 42 } } } const result = assocPath( [ 'foo', 'bar', 'baz' ], 42, { foo : null } ) expect(result).toEqual(expected)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {assocPath} from 'rambda'
interface Output { a: number, foo: {bar: number},}
describe('R.assocPath - user must explicitly set type of output', () => { it('with array as path input', () => { const result = assocPath<Output>(['foo', 'bar'], 2, {a: 1}) result // $ExpectType Output }) it('with string as path input', () => { const result = assocPath<Output>('foo.bar', 2, {a: 1}) result // $ExpectType Output })})
describe('R.assocPath - curried', () => { it('with array as path input', () => { const result = assocPath<Output>(['foo', 'bar'], 2)({a: 1}) result // $ExpectType Output }) it('with string as path input', () => { const result = assocPath<Output>('foo.bar', 2)({a: 1}) result // $ExpectType Output })})```
</details>[](#assocPath)
### binary
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.binary(%0A%20%20(a%2C%20b%2C%20c)%20%3D%3E%20a%20%2B%20b%20%2B%20c%2C%0A)(1%2C%202%2C%203%2C%204)%0A%2F%2F%20%3D%3E%203">Try this <strong>R.binary</strong> example in Rambda REPL</a>[](#binary)
### bind
```typescript
bind<F extends AnyFunction, T>(fn: F, thisObj: T): (...args: Parameters<F>) => ReturnType<F>```
Creates a function that is bound to a context.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20log%20%3D%20R.bind(console.log%2C%20console)%0Aconst%20result%20%3D%20R.pipe(%0A%20%20R.assoc('a'%2C%202)%2C%20%0A%20%20R.tap(log)%2C%20%0A%20%20R.assoc('a'%2C%203)%0A)(%7Ba%3A%201%7D)%3B%20%0A%2F%2F%20%3D%3E%20result%20-%20%60%7Ba%3A%203%7D%60%0A%2F%2F%20%3D%3E%20console%20log%20-%20%60%7Ba%3A%202%7D%60">Try this <strong>R.bind</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptbind<F extends AnyFunction, T>(fn: F, thisObj: T): (...args: Parameters<F>) => ReturnType<F>;bind<F extends AnyFunction, T>(fn: F): (thisObj: T) => (...args: Parameters<F>) => ReturnType<F>;```
</details><details><summary><strong>R.bind</strong> source</summary>```javascriptimport { curryN } from './curryN.js'
export function bind(fn, thisObj){ if (arguments.length === 1){ return _thisObj => bind(fn, _thisObj) } return curryN(fn.length, (...args) => fn.apply(thisObj, args))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { bind } from './bind.js'
function Foo(x){ this.x = x}function add(x){ return this.x + x}function Bar(x, y){ this.x = x this.y = y}Bar.prototype = new Foo()Bar.prototype.getX = function (){ return 'prototype getX'}
test('returns a function', () => { expect(typeof bind(add)(Foo)).toBe('function')})
test('returns a function bound to the specified context object', () => { const f = new Foo(12) function isFoo(){ return this instanceof Foo } const isFooBound = bind(isFoo, f) expect(isFoo()).toBeFalse() expect(isFooBound()).toBeTrue()})
test('works with built-in types', () => { const abc = bind(String.prototype.toLowerCase, 'ABCDEFG') expect(typeof abc).toBe('function') expect(abc()).toBe('abcdefg')})
test('works with user-defined types', () => { const f = new Foo(12) function getX(){ return this.x } const getXFooBound = bind(getX, f) expect(getXFooBound()).toBe(12)})
test('works with plain objects', () => { const pojso = { x : 100 } function incThis(){ return this.x + 1 } const incPojso = bind(incThis, pojso) expect(typeof incPojso).toBe('function') expect(incPojso()).toBe(101)})
test('does not interfere with existing object methods', () => { const b = new Bar('a', 'b') function getX(){ return this.x } const getXBarBound = bind(getX, b) expect(b.getX()).toBe('prototype getX') expect(getXBarBound()).toBe('a')})
test('preserves arity', () => { const f0 = function (){ return 0 } const f1 = function (a){ return a } const f2 = function (a, b){ return a + b } const f3 = function ( a, b, c ){ return a + b + c } expect(bind(f0, {})).toHaveLength(0) expect(bind(f1, {})).toHaveLength(1) expect(bind(f2, {})).toHaveLength(2) expect(bind(f3, {})).toHaveLength(3)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {bind} from 'rambda'
class Foo {}function isFoo<T = any>(this: T): boolean { return this instanceof Foo}
describe('R.bind', () => { it('happy', () => { const foo = new Foo() const result = bind(isFoo, foo)() result // $ExpectType boolean })})```
</details>[](#bind)
### both
```typescript
both(pred1: Pred, pred2: Pred): Pred```
It returns a function with `input` argument.
This function will return `true`, if both `firstCondition` and `secondCondition` return `true` when `input` is passed as their argument.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20firstCondition%20%3D%20x%20%3D%3E%20x%20%3E%2010%0Aconst%20secondCondition%20%3D%20x%20%3D%3E%20x%20%3C%2020%0Aconst%20fn%20%3D%20R.both(firstCondition%2C%20secondCondition)%0A%0Aconst%20result%20%3D%20%5Bfn(15)%2C%20fn(30)%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.both</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptboth(pred1: Pred, pred2: Pred): Pred;both<T>(pred1: Predicate<T>, pred2: Predicate<T>): Predicate<T>;both<T>(pred1: Predicate<T>): (pred2: Predicate<T>) => Predicate<T>;both(pred1: Pred): (pred2: Pred) => Pred;```
</details><details><summary><strong>R.both</strong> source</summary>```javascriptexport function both(f, g){ if (arguments.length === 1) return _g => both(f, _g) return (...input) => f(...input) && g(...input)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { both } from './both.js'
const firstFn = val => val > 0const secondFn = val => val < 10
test('with curry', () => { expect(both(firstFn)(secondFn)(17)).toBeFalse()})
test('without curry', () => { expect(both(firstFn, secondFn)(7)).toBeTrue()})
test('with multiple inputs', () => { const between = function ( a, b, c ){ return a < b && b < c } const total20 = function ( a, b, c ){ return a + b + c === 20 } const fn = both(between, total20) expect(fn( 5, 7, 8 )).toBeTrue()})
test('skip evaluation of the second expression', () => { let effect = 'not evaluated' const F = function (){ return false } const Z = function (){ effect = 'Z got evaluated' } both(F, Z)() expect(effect).toBe('not evaluated')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {both} from 'rambda'
describe('R.both', () => { it('with passed type', () => { const fn = both<number>( x => x > 1, x => x % 2 === 0 ) fn // $ExpectType Predicate<number> const result = fn(2) // $ExpectType boolean result // $ExpectType boolean }) it('with passed type - curried', () => { const fn = both<number>(x => x > 1)(x => x % 2 === 0) fn // $ExpectType Predicate<number> const result = fn(2) result // $ExpectType boolean }) it('no type passed', () => { const fn = both( x => { x // $ExpectType any return x > 1 }, x => { x // $ExpectType any return x % 2 === 0 } ) const result = fn(2) result // $ExpectType boolean }) it('no type passed - curried', () => { const fn = both((x: number) => { x // $ExpectType number return x > 1 })((x: number) => { x // $ExpectType number return x % 2 === 0 }) const result = fn(2) result // $ExpectType boolean })})```
</details>[](#both)
### call
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.call(%0A%20%20(a%2C%20b)%20%3D%3E%20a%20%2B%20b%2C%0A%20%201%2C%0A%20%202%0A)%0A%2F%2F%20%3D%3E%203">Try this <strong>R.call</strong> example in Rambda REPL</a>[](#call)
### chain
```typescript
chain<T, U>(fn: (n: T) => U[], list: T[]): U[]```
The method is also known as `flatMap`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20duplicate%20%3D%20n%20%3D%3E%20%5B%20n%2C%20n%20%5D%0Aconst%20list%20%3D%20%5B%201%2C%202%2C%203%20%5D%0A%0Aconst%20result%20%3D%20chain(duplicate%2C%20list)%0A%2F%2F%20%3D%3E%20%5B%201%2C%201%2C%202%2C%202%2C%203%2C%203%20%5D">Try this <strong>R.chain</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptchain<T, U>(fn: (n: T) => U[], list: T[]): U[];chain<T, U>(fn: (n: T) => U[]): (list: T[]) => U[];```
</details><details><summary><strong>R.chain</strong> source</summary>```javascriptexport function chain(fn, list){ if (arguments.length === 1){ return _list => chain(fn, _list) } return [].concat(...list.map(fn))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { chain as chainRamda } from 'ramda'
import { chain } from './chain.js'
const duplicate = n => [ n, n ]
test('happy', () => { const fn = x => [ x * 2 ] const list = [ 1, 2, 3 ] const result = chain(fn, list) expect(result).toEqual([ 2, 4, 6 ])})
test('maps then flattens one level', () => { expect(chain(duplicate, [ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])})
test('maps then flattens one level - curry', () => { expect(chain(duplicate)([ 1, 2, 3 ])).toEqual([ 1, 1, 2, 2, 3, 3 ])})
test('flattens only one level', () => { const nest = n => [ [ n ] ] expect(chain(nest, [ 1, 2, 3 ])).toEqual([ [ 1 ], [ 2 ], [ 3 ] ])})
test('can compose', () => { function dec(x){ return [ x - 1 ] } function times2(x){ return [ x * 2 ] } const mdouble = chain(times2) const mdec = chain(dec) expect(mdec(mdouble([ 10, 20, 30 ]))).toEqual([ 19, 39, 59 ])})
test('@types/ramda broken test', () => { const score = { maths : 90, physics : 80, } const calculateTotal = score => { const { maths, physics } = score return maths + physics } const assocTotalToScore = (total, score) => ({ ...score, total, }) const calculateAndAssocTotalToScore = chainRamda(assocTotalToScore, calculateTotal) expect(() => calculateAndAssocTotalToScore(score)).toThrowErrorMatchingInlineSnapshot('"fn(...) is not a function"')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {chain} from 'rambda'
const list = [1, 2, 3]const fn = (x: number) => [`${x}`, `${x}`]
describe('R.chain', () => { it('without passing type', () => { const result = chain(fn, list) result // $ExpectType string[] const curriedResult = chain(fn)(list) curriedResult // $ExpectType string[] })})```
</details>[](#chain)
### clamp
Restrict a number `input` to be within `min` and `max` limits.
If `input` is bigger than `max`, then the result is `max`.
If `input` is smaller than `min`, then the result is `min`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.clamp(0%2C%2010%2C%205)%2C%20%0A%20%20R.clamp(0%2C%2010%2C%20-1)%2C%0A%20%20R.clamp(0%2C%2010%2C%2011)%0A%5D%0A%2F%2F%20%3D%3E%20%5B5%2C%200%2C%2010%5D">Try this <strong>R.clamp</strong> example in Rambda REPL</a>[](#clamp)
### clone
It creates a deep copy of the `input`, which may contain (nested) Arrays and Objects, Numbers, Strings, Booleans and Dates.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20objects%20%3D%20%5B%7Ba%3A%201%7D%2C%20%7Bb%3A%202%7D%5D%3B%0Aconst%20objectsClone%20%3D%20R.clone(objects)%3B%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.equals(objects%2C%20objectsClone)%2C%0A%20%20R.equals(objects%5B0%5D%2C%20objectsClone%5B0%5D)%2C%0A%5D%20%2F%2F%20%3D%3E%20%5B%20true%2C%20true%20%5D">Try this <strong>R.clone</strong> example in Rambda REPL</a>[](#clone)
### collectBy
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.collectBy(%0A%20%20x%20%3D%3E%20x%20%25%202%2C%0A%20%20%5B1%2C%202%2C%203%2C%204%5D%0A)%0A%2F%2F%20%3D%3E%20%5B%5B2%2C%204%5D%2C%20%5B1%2C%203%5D%5D">Try this <strong>R.collectBy</strong> example in Rambda REPL</a>[](#collectBy)
### comparator
It returns a comparator function that can be used in `sort` method.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.sort(%0A%20%20R.comparator((a%2C%20b)%20%3D%3E%20a.x%20%3C%20b.x)%2C%0A%20%20%5B%7Bx%3A%202%7D%2C%20%7Bx%3A%201%7D%5D%0A)%0A%2F%2F%20%3D%3E%20%5B%7Bx%3A%201%7D%2C%20%7Bx%3A%202%7D%5D">Try this <strong>R.comparator</strong> example in Rambda REPL</a>[](#comparator)
### complement
It returns `inverted` version of `origin` function that accept `input` as argument.
The return value of `inverted` is the negative boolean value of `origin(input)`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20origin%20%3D%20x%20%3D%3E%20x%20%3E%205%0Aconst%20inverted%20%3D%20complement(origin)%0A%0Aconst%20result%20%3D%20%5B%0A%20%20origin(7)%2C%0A%20%20inverted(7)%0A%5D%20%3D%3E%20%5B%20true%2C%20false%20%5D">Try this <strong>R.complement</strong> example in Rambda REPL</a>[](#complement)
### compose
It performs right-to-left function composition.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.compose(%0A%20%20R.map(x%20%3D%3E%20x%20*%202)%2C%0A%20%20R.filter(x%20%3D%3E%20x%20%3E%202)%0A)(%5B1%2C%202%2C%203%2C%204%5D)%0A%0A%2F%2F%20%3D%3E%20%5B6%2C%208%5D">Try this <strong>R.compose</strong> example in Rambda REPL</a>[](#compose)
### composeWith
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.composeWith(%0A%20%20(fn%2C%20intermediateResult)%20%3D%3E%20fn(intermediateResult)%2C%0A%20%20%5B%0A%20%20%20%20R.map(x%20%3D%3E%20x%20%2B%201)%2C%0A%20%20%20%20R.map(x%20%3D%3E%20x%20*%202)%2C%0A%20%20%5D%0A)(%5B1%2C%202%2C%203%5D)%0A%2F%2F%20%3D%3E%20%5B3%2C%205%2C%207%5D">Try this <strong>R.composeWith</strong> example in Rambda REPL</a>[](#composeWith)
### concat
It returns a new string or array, which is the result of merging `x` and `y`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.concat(%5B1%2C%202%5D)(%5B3%2C%204%5D)%20%2F%2F%20%3D%3E%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20result%20%3D%20R.concat('foo'%2C%20'bar')%20%2F%2F%20%3D%3E%20'foobar'">Try this <strong>R.concat</strong> example in Rambda REPL</a>[](#concat)
### cond
It takes list with `conditions` and returns a new function `fn` that expects `input` as argument.
This function will start evaluating the `conditions` in order to find the first winner(order of conditions matter).
The winner is this condition, which left side returns `true` when `input` is its argument. Then the evaluation of the right side of the winner will be the final result.
If no winner is found, then `fn` returns `undefined`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20R.cond(%5B%0A%20%20%5B%20x%20%3D%3E%20x%20%3E%2025%2C%20R.always('more%20than%2025')%20%5D%2C%0A%20%20%5B%20x%20%3D%3E%20x%20%3E%2015%2C%20R.always('more%20than%2015')%20%5D%2C%0A%20%20%5B%20R.T%2C%20x%20%3D%3E%20%60%24%7Bx%7D%20is%20nothing%20special%60%20%5D%2C%0A%5D)%0A%0Aconst%20result%20%3D%20%5B%0A%20%20fn(30)%2C%0A%20%20fn(20)%2C%0A%20%20fn(10)%2C%0A%5D%20%0A%2F%2F%20%3D%3E%20%5B'more%20than%2025'%2C%20'more%20than%2015'%2C%20'10%20is%20nothing%20special'%5D">Try this <strong>R.cond</strong> example in Rambda REPL</a>[](#cond)
### converge
Accepts a converging function and a list of branching functions and returns a new function. When invoked, this new function is applied to some arguments, each branching function is applied to those same arguments. The results of each branching function are passed as arguments to the converging function to produce the return value.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.converge(R.multiply)(%5B%20R.add(1)%2C%20R.add(3)%20%5D)(2)%0A%2F%2F%20%3D%3E%2015">Try this <strong>R.converge</strong> example in Rambda REPL</a>[](#converge)
### count
It counts how many times `predicate` function returns `true`, when supplied with iteration of `list`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%7Ba%3A%201%7D%2C%201%2C%20%7Ba%3A2%7D%5D%0Aconst%20result%20%3D%20R.count(x%20%3D%3E%20x.a%20!%3D%3D%20undefined%2C%20list)%0A%2F%2F%20%3D%3E%202">Try this <strong>R.count</strong> example in Rambda REPL</a>[](#count)
### countBy
```typescript
countBy<T extends unknown>(transformFn: (x: T) => any, list: T[]): Record<string, number>```
It counts elements in a list after each instance of the input list is passed through `transformFn` function.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%20'a'%2C%20'A'%2C%20'b'%2C%20'B'%2C%20'c'%2C%20'C'%20%5D%0A%0Aconst%20result%20%3D%20countBy(R.toLower%2C%20list)%0Aconst%20expected%20%3D%20%7B%20a%3A%202%2C%20b%3A%202%2C%20c%3A%202%20%7D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.countBy</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptcountBy<T extends unknown>(transformFn: (x: T) => any, list: T[]): Record<string, number>;countBy<T extends unknown>(transformFn: (x: T) => any): (list: T[]) => Record<string, number>;```
</details><details><summary><strong>R.countBy</strong> source</summary>```javascriptexport function countBy(fn, list){ if (arguments.length === 1){ return _list => countBy(fn, _list) } const willReturn = {} list.forEach(item => { const key = fn(item) if (!willReturn[ key ]){ willReturn[ key ] = 1 } else { willReturn[ key ]++ } }) return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { countBy } from './countBy.js'
const list = [ 'a', 'A', 'b', 'B', 'c', 'C' ]
test('happy', () => { const result = countBy(x => x.toLowerCase(), list) expect(result).toEqual({ a : 2, b : 2, c : 2, })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {countBy} from 'rambda'
const transformFn = (x: string) => x.toLowerCase()const list = ['a', 'A', 'b', 'B', 'c', 'C']
describe('R.countBy', () => { it('happy', () => { const result = countBy(transformFn, list) result // $ExpectType Record<string, number> }) it('curried', () => { const result = countBy(transformFn)(list) result // $ExpectType Record<string, number> })})```
</details>[](#countBy)
### curry
It expects a function as input and returns its curried version.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20(a%2C%20b%2C%20c)%20%3D%3E%20a%20%2B%20b%20%2B%20c%0Aconst%20curried%20%3D%20R.curry(fn)%0Aconst%20sum%20%3D%20curried(1%2C2)%0A%0Aconst%20result%20%3D%20sum(3)%20%2F%2F%20%3D%3E%206">Try this <strong>R.curry</strong> example in Rambda REPL</a>[](#curry)
### curryN
It returns a curried equivalent of the provided function, with the specified arity.
[](#curryN)
### dec
It decrements a number.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.dec(2)%20%2F%2F%20%3D%3E%201">Try this <strong>R.dec</strong> example in Rambda REPL</a>[](#dec)
### defaultTo
```typescript
defaultTo<T>(defaultValue: T, input: T | null | undefined): T```
It returns `defaultValue`, if all of `inputArguments` are `undefined`, `null` or `NaN`.
Else, it returns the first truthy `inputArguments` instance(from left to right).
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.defaultTo('foo'%2C%20'bar')%20%2F%2F%20%3D%3E%20'bar'%0AR.defaultTo('foo'%2C%20undefined)%20%2F%2F%20%3D%3E%20'foo'%0A%0A%2F%2F%20Important%20-%20emtpy%20string%20is%20not%20falsy%20value(same%20as%20Ramda)%0Aconst%20result%20%3D%20R.defaultTo('foo'%2C%20'')%20%2F%2F%20%3D%3E%20'foo'">Try this <strong>R.defaultTo</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptdefaultTo<T>(defaultValue: T, input: T | null | undefined): T;defaultTo<T>(defaultValue: T): (input: T | null | undefined) => T;```
</details><details><summary><strong>R.defaultTo</strong> source</summary>```javascriptfunction isFalsy(input){ return ( input === undefined || input === null || Number.isNaN(input) === true )}
export function defaultTo(defaultArgument, input){ if (arguments.length === 1){ return _input => defaultTo(defaultArgument, _input) } return isFalsy(input) ? defaultArgument : input}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { defaultTo } from './defaultTo.js'
test('with undefined', () => { expect(defaultTo('foo')(undefined)).toBe('foo')})
test('with null', () => { expect(defaultTo('foo')(null)).toBe('foo')})
test('with NaN', () => { expect(defaultTo('foo')(NaN)).toBe('foo')})
test('with empty string', () => { expect(defaultTo('foo', '')).toBe('')})
test('with false', () => { expect(defaultTo('foo', false)).toBeFalse()})
test('when inputArgument passes initial check', () => { expect(defaultTo('foo', 'bar')).toBe('bar')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {defaultTo} from 'rambda'
describe('R.defaultTo with Ramda spec', () => { it('happy', () => { const result = defaultTo('foo', '') result // $ExpectType "" | "foo" }) it('with explicit type', () => { const result = defaultTo<string>('foo', null) result // $ExpectType string })})```
</details>[](#defaultTo)
### descend
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.sort(%0A%20%20R.descend(x%20%3D%3E%20x)%2C%0A%20%20%5B1%2C%202%5D%0Aconst%20result%20%3D%20)%0A%2F%2F%20%3D%3E%20%5B2%2C%201%5D">Try this <strong>R.descend</strong> example in Rambda REPL</a>[](#descend)
### difference
```typescript
difference<T>(a: T[], b: T[]): T[]```
It returns the uniq set of all elements in the first list `a` not contained in the second list `b`.
`R.equals` is used to determine equality.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20a%20%3D%20%5B%201%2C%202%2C%203%2C%204%20%5D%0Aconst%20b%20%3D%20%5B%203%2C%204%2C%205%2C%206%20%5D%0A%0Aconst%20result%20%3D%20R.difference(a%2C%20b)%0A%2F%2F%20%3D%3E%20%5B%201%2C%202%20%5D">Try this <strong>R.difference</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptdifference<T>(a: T[], b: T[]): T[];difference<T>(a: T[]): (b: T[]) => T[];```
</details><details><summary><strong>R.difference</strong> source</summary>```javascriptimport { includes } from './includes.js'import { uniq } from './uniq.js'
export function difference(a, b){ if (arguments.length === 1) return _b => difference(a, _b) return uniq(a).filter(aInstance => !includes(aInstance, b))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { difference as differenceRamda } from 'ramda'
import { difference } from './difference.js'
test('difference', () => { const a = [ 1, 2, 3, 4 ] const b = [ 3, 4, 5, 6 ] expect(difference(a)(b)).toEqual([ 1, 2 ]) expect(difference([], [])).toEqual([])})
test('difference with objects', () => { const a = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ] const b = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ] expect(difference(a, b)).toEqual([ { id : 1 }, { id : 2 } ])})
test('no duplicates in first list', () => { const M2 = [ 1, 2, 3, 4, 1, 2, 3, 4 ] const N2 = [ 3, 3, 4, 4, 5, 5, 6, 6 ] expect(difference(M2, N2)).toEqual([ 1, 2 ])})
test('should use R.equals', () => { expect(difference([ 1 ], [ 1 ])).toHaveLength(0) expect(differenceRamda([ NaN ], [ NaN ])).toHaveLength(0)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {difference} from 'rambda'
const list1 = [1, 2, 3]const list2 = [1, 2, 4]
describe('R.difference', () => { it('happy', () => { const result = difference(list1, list2) result // $ExpectType number[] }) it('curried', () => { const result = difference(list1)(list2) result // $ExpectType number[] })})```
</details>[](#difference)
### differenceWith
```typescript
differenceWith<T1, T2>( pred: (a: T1, b: T2) => boolean, list1: T1[], list2: T2[],): T1[]```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.differenceWith(%0A%20%20(a%2C%20b)%20%3D%3E%20a.x%20%3D%3D%3D%20b.x%2C%0A%20%20%5B%7Bx%3A%201%7D%2C%20%7Bx%3A%202%7D%5D%2C%0A%20%20%5B%7Bx%3A%201%7D%2C%20%7Bx%3A%203%7D%5D%0A)%0A%2F%2F%20%3D%3E%20%5B%7Bx%3A%202%7D%5D">Try this <strong>R.differenceWith</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptdifferenceWith<T1, T2>( pred: (a: T1, b: T2) => boolean, list1: T1[], list2: T2[],): T1[];differenceWith<T1, T2>( pred: (a: T1, b: T2) => boolean,): (list1: T1[], list2: T2[]) => T1[];differenceWith<T1, T2>( pred: (a: T1, b: T2) => boolean, list1: T1[],): (list2: T2[]) => T1[];```
</details><details><summary><strong>R.differenceWith</strong> source</summary>```javascriptimport { curry } from './curry.js'import { _indexOf } from './equals.js'
export function differenceWithFn( fn, a, b){ const willReturn = [] const [ first, second ] = a.length > b.length ? [ a, b ] : [ b, a ] first.forEach(item => { const hasItem = second.some(secondItem => fn(item, secondItem)) if (!hasItem && _indexOf(item, willReturn) === -1){ willReturn.push(item) } }) return willReturn}
export const differenceWith = curry(differenceWithFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { differenceWith } from './differenceWith.js'
test('happy', () => { const foo = [ { a : 1 }, { a : 2 }, { a : 3 } ] const bar = [ { a : 3 }, { a : 4 } ] const fn = function (r, s){ return r.a === s.a } const result = differenceWith( fn, foo, bar ) expect(result).toEqual([ { a : 1 }, { a : 2 } ])})```
</details>[](#differenceWith)
### dissoc
It returns a new object that does not contain property `prop`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.dissoc('b'%2C%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%201%2C%20c%3A%203%7D">Try this <strong>R.dissoc</strong> example in Rambda REPL</a>[](#dissoc)
### dissocPath
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.dissocPath(%5B'a'%2C%20'b'%5D%2C%20%7Ba%3A%20%7Bb%3A%201%2C%20c%3A%202%7D%7D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%20%7Bc%3A%202%7D%7D">Try this <strong>R.dissocPath</strong> example in Rambda REPL</a>[](#dissocPath)
### divide
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.divide(71%2C%20100)%20%2F%2F%20%3D%3E%200.71">Try this <strong>R.divide</strong> example in Rambda REPL</a>[](#divide)
### drop
```typescript
drop<T>(howMany: number, input: T[]): T[]```
It returns `howMany` items dropped from beginning of list or string `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.drop(2%2C%20%5B'foo'%2C%20'bar'%2C%20'baz'%5D)%20%2F%2F%20%3D%3E%20%5B'baz'%5D%0Aconst%20result%20%3D%20R.drop(2%2C%20'foobar')%20%20%2F%2F%20%3D%3E%20'obar'">Try this <strong>R.drop</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptdrop<T>(howMany: number, input: T[]): T[];drop(howMany: number, input: string): string;drop<T>(howMany: number): { <T>(input: T[]): T[]; (input: string): string;};```
</details><details><summary><strong>R.drop</strong> source</summary>```javascriptexport function drop(howManyToDrop, listOrString){ if (arguments.length === 1) return _list => drop(howManyToDrop, _list) return listOrString.slice(howManyToDrop > 0 ? howManyToDrop : 0)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport assert from 'assert'
import { drop } from './drop.js'
test('with array', () => { expect(drop(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ]) expect(drop(3, [ 'foo', 'bar', 'baz' ])).toEqual([]) expect(drop(4, [ 'foo', 'bar', 'baz' ])).toEqual([])})
test('with string', () => { expect(drop(3, 'rambda')).toBe('bda')})
test('with non-positive count', () => { expect(drop(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ]) expect(drop(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ]) expect(drop(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])})
test('should return copy', () => { const xs = [ 1, 2, 3 ] assert.notStrictEqual(drop(0, xs), xs) assert.notStrictEqual(drop(-1, xs), xs)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {drop} from 'rambda'
const list = [1, 2, 3, 4]const str = 'foobar'const howMany = 2
describe('R.drop - array', () => { it('happy', () => { const result = drop(howMany, list) result // $ExpectType number[] }) it('curried', () => { const result = drop(howMany)(list) result // $ExpectType number[] })})
describe('R.drop - string', () => { it('happy', () => { const result = drop(howMany, str) result // $ExpectType string }) it('curried', () => { const result = drop(howMany)(str) result // $ExpectType string })})```
</details>[](#drop)
### dropLast
```typescript
dropLast<T>(howMany: number, input: T[]): T[]```
It returns `howMany` items dropped from the end of list or string `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.dropLast(2%2C%20%5B'foo'%2C%20'bar'%2C%20'baz'%5D)%20%2F%2F%20%3D%3E%20%5B'foo'%5D%0Aconst%20result%20%3D%20R.dropLast(2%2C%20'foobar')%20%20%2F%2F%20%3D%3E%20'foob'">Try this <strong>R.dropLast</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptdropLast<T>(howMany: number, input: T[]): T[];dropLast(howMany: number, input: string): string;dropLast<T>(howMany: number): { <T>(input: T[]): T[]; (input: string): string;};```
</details><details><summary><strong>R.dropLast</strong> source</summary>```javascriptexport function dropLast(howManyToDrop, listOrString){ if (arguments.length === 1){ return _listOrString => dropLast(howManyToDrop, _listOrString) } return howManyToDrop > 0 ? listOrString.slice(0, -howManyToDrop) : listOrString.slice()}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport assert from 'assert'
import { dropLast } from './dropLast.js'
test('with array', () => { expect(dropLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo' ]) expect(dropLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([]) expect(dropLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([])})
test('with string', () => { expect(dropLast(3, 'rambda')).toBe('ram')})
test('with non-positive count', () => { expect(dropLast(0, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ]) expect(dropLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ]) expect(dropLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])})
test('should return copy', () => { const xs = [ 1, 2, 3 ] assert.notStrictEqual(dropLast(0, xs), xs) assert.notStrictEqual(dropLast(-1, xs), xs)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {dropLast} from 'rambda'
const list = [1, 2, 3, 4]const str = 'foobar'const howMany = 2
describe('R.dropLast - array', () => { it('happy', () => { const result = dropLast(howMany, list) result // $ExpectType number[] }) it('curried', () => { const result = dropLast(howMany)(list) result // $ExpectType number[] })})
describe('R.dropLast - string', () => { it('happy', () => { const result = dropLast(howMany, str) result // $ExpectType string }) it('curried', () => { const result = dropLast(howMany)(str) result // $ExpectType string })})```
</details>[](#dropLast)
### dropLastWhile
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%2C%205%5D%3B%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3E%3D%203%0A%0Aconst%20result%20%3D%20dropLastWhile(predicate%2C%20list)%3B%0A%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.dropLastWhile</strong> example in Rambda REPL</a>[](#dropLastWhile)
### dropRepeats
```typescript
dropRepeats<T>(list: T[]): T[]```
It removes any successive duplicates according to `R.equals`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.dropRepeats(%5B%0A%20%201%2C%20%0A%20%201%2C%20%0A%20%20%7Ba%3A%201%7D%2C%20%0A%20%20%7Ba%3A1%7D%2C%20%0A%20%201%0A%5D)%0A%2F%2F%20%3D%3E%20%5B1%2C%20%7Ba%3A%201%7D%2C%201%5D">Try this <strong>R.dropRepeats</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptdropRepeats<T>(list: T[]): T[];```
</details><details><summary><strong>R.dropRepeats</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'import { equals } from './equals.js'
export function dropRepeats(list){ if (!isArray(list)){ throw new Error(`${ list } is not a list`) } const toReturn = [] list.reduce((prev, current) => { if (!equals(prev, current)){ toReturn.push(current) } return current }, undefined) return toReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { dropRepeats as dropRepeatsRamda } from 'ramda'
import { compareCombinations } from './_internals/testUtils.js'import { add } from './add.js'import { dropRepeats } from './dropRepeats.js'
const list = [ 1, 2, 2, 2, 3, 4, 4, 5, 5, 3, 2, 2, { a : 1 }, { a : 1 } ]const listClean = [ 1, 2, 3, 4, 5, 3, 2, { a : 1 } ]
test('happy', () => { const result = dropRepeats(list) expect(result).toEqual(listClean)})
const possibleLists = [ [ add(1), async () => {}, [ 1 ], [ 1 ], [ 2 ], [ 2 ] ], [ add(1), add(1), add(2) ], [], 1, /foo/g, Promise.resolve(1),]
describe('brute force', () => { compareCombinations({ firstInput : possibleLists, callback : errorsCounters => { expect(errorsCounters).toMatchInlineSnapshot(` { "ERRORS_MESSAGE_MISMATCH": 0, "ERRORS_TYPE_MISMATCH": 0, "RESULTS_MISMATCH": 1, "SHOULD_NOT_THROW": 3, "SHOULD_THROW": 0, "TOTAL_TESTS": 6, } `) }, fn : dropRepeats, fnRamda : dropRepeatsRamda, })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {dropRepeats} from 'rambda'
describe('R.dropRepeats', () => { it('happy', () => { const result = dropRepeats([1, 2, 2, 3]) result // $ExpectType number[] })})```
</details>[](#dropRepeats)
### dropRepeatsBy
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.dropRepeatsBy(%0A%20%20Math.abs%2C%0A%20%20%5B1%2C%20-1%2C%202%2C%203%2C%20-3%5D%0A)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%203%5D">Try this <strong>R.dropRepeatsBy</strong> example in Rambda REPL</a>[](#dropRepeatsBy)
### dropRepeatsWith
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%7Ba%3A1%2Cb%3A2%7D%2C%20%7Ba%3A1%2Cb%3A3%7D%2C%20%7Ba%3A2%2C%20b%3A4%7D%5D%0Aconst%20result%20%3D%20R.dropRepeatsWith(R.prop('a')%2C%20list)%0A%0A%2F%2F%20%3D%3E%20%5B%7Ba%3A1%2Cb%3A2%7D%2C%20%7Ba%3A2%2C%20b%3A4%7D%5D">Try this <strong>R.dropRepeatsWith</strong> example in Rambda REPL</a>[](#dropRepeatsWith)
### dropWhile
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3C%203%0Aconst%20result%20%3D%20R.dropWhile(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20%5B3%2C%204%5D">Try this <strong>R.dropWhile</strong> example in Rambda REPL</a>[](#dropWhile)
### either
```typescript
either(firstPredicate: Pred, secondPredicate: Pred): Pred```
It returns a new `predicate` function from `firstPredicate` and `secondPredicate` inputs.
This `predicate` function will return `true`, if any of the two input predicates return `true`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20firstPredicate%20%3D%20x%20%3D%3E%20x%20%3E%2010%0Aconst%20secondPredicate%20%3D%20x%20%3D%3E%20x%20%25%202%20%3D%3D%3D%200%0Aconst%20predicate%20%3D%20R.either(firstPredicate%2C%20secondPredicate)%0A%0Aconst%20result%20%3D%20%5B%0A%20%20predicate(15)%2C%0A%20%20predicate(8)%2C%0A%20%20predicate(7)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%2C%20false%5D">Try this <strong>R.either</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripteither(firstPredicate: Pred, secondPredicate: Pred): Pred;either<T>(firstPredicate: Predicate<T>, secondPredicate: Predicate<T>): Predicate<T>;either<T>(firstPredicate: Predicate<T>): (secondPredicate: Predicate<T>) => Predicate<T>;either(firstPredicate: Pred): (secondPredicate: Pred) => Pred;```
</details><details><summary><strong>R.either</strong> source</summary>```javascriptexport function either(firstPredicate, secondPredicate){ if (arguments.length === 1){ return _secondPredicate => either(firstPredicate, _secondPredicate) } return (...input) => Boolean(firstPredicate(...input) || secondPredicate(...input))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { either } from './either.js'
test('with multiple inputs', () => { const between = function ( a, b, c ){ return a < b && b < c } const total20 = function ( a, b, c ){ return a + b + c === 20 } const fn = either(between, total20) expect(fn( 7, 8, 5 )).toBeTrue()})
test('skip evaluation of the second expression', () => { let effect = 'not evaluated' const F = function (){ return true } const Z = function (){ effect = 'Z got evaluated' } either(F, Z)() expect(effect).toBe('not evaluated')})
test('case 1', () => { const firstFn = val => val > 0 const secondFn = val => val * 5 > 10 expect(either(firstFn, secondFn)(1)).toBeTrue()})
test('case 2', () => { const firstFn = val => val > 0 const secondFn = val => val === -10 const fn = either(firstFn)(secondFn) expect(fn(-10)).toBeTrue()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {either} from 'rambda'
describe('R.either', () => { it('with passed type', () => { const fn = either<number>( x => x > 1, x => x % 2 === 0 ) fn // $ExpectType Predicate<number> const result = fn(2) // $ExpectType boolean result // $ExpectType boolean }) it('with passed type - curried', () => { const fn = either<number>(x => x > 1)(x => x % 2 === 0) fn // $ExpectType Predicate<number> const result = fn(2) result // $ExpectType boolean }) it('no type passed', () => { const fn = either( x => { x // $ExpectType any return x > 1 }, x => { x // $ExpectType any return x % 2 === 0 } ) const result = fn(2) result // $ExpectType boolean }) it('no type passed - curried', () => { const fn = either((x: number) => { x // $ExpectType number return x > 1 })((x: number) => { x // $ExpectType number return x % 2 === 0 }) const result = fn(2) result // $ExpectType boolean })})```
</details>[](#either)
### empty
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5BR.empty(%5B1%2C2%2C3%5D)%2C%20R.empty('foo')%2C%20R.empty(%7Bx%3A%201%2C%20y%3A%202%7D)%5D%0A%2F%2F%20%3D%3E%20%5B%5B%5D%2C%20''%2C%20%7B%7D%5D">Try this <strong>R.empty</strong> example in Rambda REPL</a>[](#empty)
### endsWith
```typescript
endsWith<T extends string>(question: T, str: string): boolean```
When iterable is a string, then it behaves as `String.prototype.endsWith`.When iterable is a list, then it uses R.equals to determine if the target list ends in the same way as the given target.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20str%20%3D%20'foo-bar'%0Aconst%20list%20%3D%20%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%2C%20%7Ba%3A3%7D%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.endsWith('bar'%2C%20str)%2C%0A%20%20R.endsWith(%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%5D%2C%20list)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%5D">Try this <strong>R.endsWith</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptendsWith<T extends string>(question: T, str: string): boolean;endsWith<T extends string>(question: T): (str: string) => boolean;endsWith<T>(question: T[], list: T[]): boolean;endsWith<T>(question: T[]): (list: T[]) => boolean;```
</details><details><summary><strong>R.endsWith</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'import { equals } from './equals.js'
export function endsWith(target, iterable){ if (arguments.length === 1) return _iterable => endsWith(target, _iterable) if (typeof iterable === 'string'){ return iterable.endsWith(target) } if (!isArray(target)) return false const diff = iterable.length - target.length let correct = true const filtered = target.filter((x, index) => { if (!correct) return false const result = equals(x, iterable[ index + diff ]) if (!result) correct = false return result }) return filtered.length === target.length}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { endsWith as endsWithRamda } from 'ramda'
import { compareCombinations } from './_internals/testUtils.js'import { endsWith } from './endsWith.js'
test('with string', () => { expect(endsWith('bar', 'foo-bar')).toBeTrue() expect(endsWith('baz')('foo-bar')).toBeFalse()})
test('use R.equals with array', () => { const list = [ { a : 1 }, { a : 2 }, { a : 3 } ] expect(endsWith({ a : 3 }, list)).toBeFalse(), expect(endsWith([ { a : 3 } ], list)).toBeTrue() expect(endsWith([ { a : 2 }, { a : 3 } ], list)).toBeTrue() expect(endsWith(list, list)).toBeTrue() expect(endsWith([ { a : 1 } ], list)).toBeFalse()})
export const possibleTargets = [ NaN, [ NaN ], /foo/, [ /foo/ ], Promise.resolve(1), [ Promise.resolve(1) ], Error('foo'), [ Error('foo') ],]
export const possibleIterables = [ [ Promise.resolve(1), Promise.resolve(2) ], [ /foo/, /bar/ ], [ NaN ], [ Error('foo'), Error('bar') ],]
describe('brute force', () => { compareCombinations({ fn : endsWith, fnRamda : endsWithRamda, firstInput : possibleTargets, secondInput : possibleIterables, callback : errorsCounters => { expect(errorsCounters).toMatchInlineSnapshot(` { "ERRORS_MESSAGE_MISMATCH": 0, "ERRORS_TYPE_MISMATCH": 0, "RESULTS_MISMATCH": 0, "SHOULD_NOT_THROW": 0, "SHOULD_THROW": 0, "TOTAL_TESTS": 32, } `) }, })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {endsWith} from 'rambda'
describe('R.endsWith - array', () => { const target = [{a: 2}] const input = [{a: 1}, {a: 2}] it('happy', () => { const result = endsWith(target, input) result // $ExpectType boolean }) it('curried', () => { const result = endsWith(target)(input) result // $ExpectType boolean })})
describe('R.endsWith - string', () => { const target = 'bar' const input = 'foo bar' it('happy', () => { const result = endsWith(target, input) result // $ExpectType boolean }) it('curried', () => { const result = endsWith(target)(input) result // $ExpectType boolean })})```
</details>[](#endsWith)
### eqBy
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.eqBy(Math.abs%2C%205%2C%20-5)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.eqBy</strong> example in Rambda REPL</a>[](#eqBy)
### eqProps
It returns `true` if property `prop` in `obj1` is equal to property `prop` in `obj2` according to `R.equals`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj1%20%3D%20%7Ba%3A%201%2C%20b%3A2%7D%0Aconst%20obj2%20%3D%20%7Ba%3A%201%2C%20b%3A3%7D%0Aconst%20result%20%3D%20R.eqProps('a'%2C%20obj1%2C%20obj2)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.eqProps</strong> example in Rambda REPL</a>[](#eqProps)
### equals
```typescript
equals<T>(x: T, y: T): boolean```
It deeply compares `x` and `y` and returns `true` if they are equal.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.equals(%0A%20%20%5B1%2C%20%7Ba%3A2%7D%2C%20%5B%7Bb%3A%203%7D%5D%5D%2C%0A%20%20%5B1%2C%20%7Ba%3A2%7D%2C%20%5B%7Bb%3A%203%7D%5D%5D%0Aconst%20result%20%3D%20)%20%2F%2F%20%3D%3E%20true">Try this <strong>R.equals</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptequals<T>(x: T, y: T): boolean;equals<T>(x: T): (y: T) => boolean;```
</details><details><summary><strong>R.equals</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'import { type } from './type.js'
export function _lastIndexOf(valueToFind, list){ if (!isArray(list)) throw new Error(`Cannot read property 'indexOf' of ${ list }`) const typeOfValue = type(valueToFind) if (![ 'Array', 'NaN', 'Object', 'RegExp' ].includes(typeOfValue)) return list.lastIndexOf(valueToFind) const { length } = list let index = length let foundIndex = -1 while (--index > -1 && foundIndex === -1) if (equals(list[ index ], valueToFind)) foundIndex = index return foundIndex}
export function _indexOf(valueToFind, list){ if (!isArray(list)) throw new Error(`Cannot read property 'indexOf' of ${ list }`) const typeOfValue = type(valueToFind) if (![ 'Array', 'NaN', 'Object', 'RegExp' ].includes(typeOfValue)) return list.indexOf(valueToFind) let index = -1 let foundIndex = -1 const { length } = list while (++index < length && foundIndex === -1) if (equals(list[ index ], valueToFind)) foundIndex = index return foundIndex}
function _arrayFromIterator(iter){ const list = [] let next while (!(next = iter.next()).done) list.push(next.value) return list}
function _compareSets(a, b){ if (a.size !== b.size) return false const aList = _arrayFromIterator(a.values()) const bList = _arrayFromIterator(b.values()) const filtered = aList.filter(aInstance => _indexOf(aInstance, bList) === -1) return filtered.length === 0}
function compareErrors(a, b){ if (a.message !== b.message) return false if (a.toString !== b.toString) return false return a.toString() === b.toString()}
function parseDate(maybeDate){ if (!maybeDate.toDateString) return [ false ] return [ true, maybeDate.getTime() ]}
function parseRegex(maybeRegex){ if (maybeRegex.constructor !== RegExp) return [ false ] return [ true, maybeRegex.toString() ]}
export function equals(a, b){ if (arguments.length === 1) return _b => equals(a, _b) if (Object.is(a, b)) return true const aType = type(a) if (aType !== type(b)) return false if (aType === 'Function') return a.name === undefined ? false : a.name === b.name if ([ 'NaN', 'Null', 'Undefined' ].includes(aType)) return true if ([ 'BigInt', 'Number' ].includes(aType)){ if (Object.is(-0, a) !== Object.is(-0, b)) return false return a.toString() === b.toString() } if ([ 'Boolean', 'String' ].includes(aType)) return a.toString() === b.toString() if (aType === 'Array'){ const aClone = Array.from(a) const bClone = Array.from(b) if (aClone.toString() !== bClone.toString()) return false let loopArrayFlag = true aClone.forEach((aCloneInstance, aCloneIndex) => { if (loopArrayFlag) if ( aCloneInstance !== bClone[ aCloneIndex ] && !equals(aCloneInstance, bClone[ aCloneIndex ]) ) loopArrayFlag = false }) return loopArrayFlag } const aRegex = parseRegex(a) const bRegex = parseRegex(b) if (aRegex[ 0 ]) return bRegex[ 0 ] ? aRegex[ 1 ] === bRegex[ 1 ] : false else if (bRegex[ 0 ]) return false const aDate = parseDate(a) const bDate = parseDate(b) if (aDate[ 0 ]) return bDate[ 0 ] ? aDate[ 1 ] === bDate[ 1 ] : false else if (bDate[ 0 ]) return false if (a instanceof Error){ if (!(b instanceof Error)) return false return compareErrors(a, b) } if (aType === 'Set') return _compareSets(a, b) if (aType === 'Object'){ const aKeys = Object.keys(a) if (aKeys.length !== Object.keys(b).length) return false let loopObjectFlag = true aKeys.forEach(aKeyInstance => { if (loopObjectFlag){ const aValue = a[ aKeyInstance ] const bValue = b[ aKeyInstance ] if (aValue !== bValue && !equals(aValue, bValue)) loopObjectFlag = false } }) return loopObjectFlag } return false}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { equals as equalsRamda } from 'ramda'
import { compareCombinations } from './_internals/testUtils.js'import { variousTypes } from './benchmarks/_utils.js'import { equals } from './equals.js'
test('compare functions', () => { function foo(){} function bar(){} const baz = () => {} const expectTrue = equals(foo, foo) const expectFalseFirst = equals(foo, bar) const expectFalseSecond = equals(foo, baz) expect(expectTrue).toBeTrue() expect(expectFalseFirst).toBeFalse() expect(expectFalseSecond).toBeFalse()})
test('with array of objects', () => { const list1 = [ { a : 1 }, [ { b : 2 } ] ] const list2 = [ { a : 1 }, [ { b : 2 } ] ] const list3 = [ { a : 1 }, [ { b : 3 } ] ] expect(equals(list1, list2)).toBeTrue() expect(equals(list1, list3)).toBeFalse()})
test('with regex', () => { expect(equals(/s/, /s/)).toBeTrue() expect(equals(/s/, /d/)).toBeFalse() expect(equals(/a/gi, /a/gi)).toBeTrue() expect(equals(/a/gim, /a/gim)).toBeTrue() expect(equals(/a/gi, /a/i)).toBeFalse()})
test('not a number', () => { expect(equals([ NaN ], [ NaN ])).toBeTrue()})
test('new number', () => { expect(equals(new Number(0), new Number(0))).toBeTrue() expect(equals(new Number(0), new Number(1))).toBeFalse() expect(equals(new Number(1), new Number(0))).toBeFalse()})
test('new string', () => { expect(equals(new String(''), new String(''))).toBeTrue() expect(equals(new String(''), new String('x'))).toBeFalse() expect(equals(new String('x'), new String(''))).toBeFalse() expect(equals(new String('foo'), new String('foo'))).toBeTrue() expect(equals(new String('foo'), new String('bar'))).toBeFalse() expect(equals(new String('bar'), new String('foo'))).toBeFalse()})
test('new Boolean', () => { expect(equals(new Boolean(true), new Boolean(true))).toBeTrue() expect(equals(new Boolean(false), new Boolean(false))).toBeTrue() expect(equals(new Boolean(true), new Boolean(false))).toBeFalse() expect(equals(new Boolean(false), new Boolean(true))).toBeFalse()})
test('new Error', () => { expect(equals(new Error('XXX'), {})).toBeFalse() expect(equals(new Error('XXX'), new TypeError('XXX'))).toBeFalse() expect(equals(new Error('XXX'), new Error('YYY'))).toBeFalse() expect(equals(new Error('XXX'), new Error('XXX'))).toBeTrue() expect(equals(new Error('XXX'), new TypeError('YYY'))).toBeFalse() expect(equals(new Error('XXX'), new Error('XXX'))).toBeTrue()})
test('with dates', () => { expect(equals(new Date(0), new Date(0))).toBeTrue() expect(equals(new Date(1), new Date(1))).toBeTrue() expect(equals(new Date(0), new Date(1))).toBeFalse() expect(equals(new Date(1), new Date(0))).toBeFalse() expect(equals(new Date(0), {})).toBeFalse() expect(equals({}, new Date(0))).toBeFalse()})
test('ramda spec', () => { expect(equals({}, {})).toBeTrue() expect(equals({ a : 1, b : 2, }, { a : 1, b : 2, })).toBeTrue() expect(equals({ a : 2, b : 3, }, { a : 2, b : 3, })).toBeTrue() expect(equals({ a : 2, b : 3, }, { a : 3, b : 3, })).toBeFalse() expect(equals({ a : 2, b : 3, c : 1, }, { a : 2, b : 3, })).toBeFalse()})
test('works with boolean tuple', () => { expect(equals([ true, false ], [ true, false ])).toBeTrue() expect(equals([ true, false ], [ true, true ])).toBeFalse()})
test('works with equal objects within array', () => { const objFirst = { a : { b : 1, c : 2, d : [ 1 ], }, } const objSecond = { a : { b : 1, c : 2, d : [ 1 ], }, } const x = [ 1, 2, objFirst, null, '', [] ] const y = [ 1, 2, objSecond, null, '', [] ] expect(equals(x, y)).toBeTrue()})
test('works with different objects within array', () => { const objFirst = { a : { b : 1 } } const objSecond = { a : { b : 2 } } const x = [ 1, 2, objFirst, null, '', [] ] const y = [ 1, 2, objSecond, null, '', [] ] expect(equals(x, y)).toBeFalse()})
test('works with undefined as second argument', () => { expect(equals(1, undefined)).toBeFalse() expect(equals(undefined, undefined)).toBeTrue()})
test('compare sets', () => { const toCompareDifferent = new Set([ { a : 1 }, { a : 2 } ]) const toCompareSame = new Set([ { a : 1 }, { a : 2 }, { a : 1 } ]) const testSet = new Set([ { a : 1 }, { a : 2 }, { a : 1 } ]) expect(equals(toCompareSame, testSet)).toBeTruthy() expect(equals(toCompareDifferent, testSet)).toBeFalsy() expect(equalsRamda(toCompareSame, testSet)).toBeTruthy() expect(equalsRamda(toCompareDifferent, testSet)).toBeFalsy()})
test('compare simple sets', () => { const testSet = new Set([ '2', '3', '3', '2', '1' ]) expect(equals(new Set([ '3', '2', '1' ]), testSet)).toBeTruthy() expect(equals(new Set([ '3', '2', '0' ]), testSet)).toBeFalsy()})
test('various examples', () => { expect(equals([ 1, 2, 3 ])([ 1, 2, 3 ])).toBeTrue() expect(equals([ 1, 2, 3 ], [ 1, 2 ])).toBeFalse() expect(equals(1, 1)).toBeTrue() expect(equals(1, '1')).toBeFalse() expect(equals({}, {})).toBeTrue() expect(equals({ a : 1, b : 2, }, { a : 1, b : 2, })).toBeTrue() expect(equals({ a : 1, b : 2, }, { a : 1, b : 1, })).toBeFalse() expect(equals({ a : 1, b : false, }, { a : 1, b : 1, })).toBeFalse() expect(equals({ a : 1, b : 2, }, { a : 1, b : 2, c : 3, })).toBeFalse() expect(equals({ x : { a : 1, b : 2, }, }, { x : { a : 1, b : 2, c : 3, }, })).toBeFalse() expect(equals({ a : 1, b : 2, }, { a : 1, b : 3, })).toBeFalse() expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 1 } } })).toBeTrue() expect(equals({ a : { b : { c : 1 } } }, { a : { b : { c : 2 } } })).toBeFalse() expect(equals({ a : {} }, { a : {} })).toBeTrue() expect(equals('', '')).toBeTrue() expect(equals('foo', 'foo')).toBeTrue() expect(equals('foo', 'bar')).toBeFalse() expect(equals(0, false)).toBeFalse() expect(equals(/\s/g, null)).toBeFalse() expect(equals(null, null)).toBeTrue() expect(equals(false)(null)).toBeFalse()})
test('with custom functions', () => { function foo(){ return 1 } foo.prototype.toString = () => '' const result = equals(foo, foo) expect(result).toBeTrue()})
test('with classes', () => { class Foo{} const foo = new Foo() const result = equals(foo, foo) expect(result).toBeTrue()})
test('with negative zero', () => { expect(equals(-0, -0)).toBeTrue() expect(equals(-0, 0)).toBeFalse() expect(equals(0, 0)).toBeTrue() expect(equals(-0, 1)).toBeFalse()})
test('with big int', () => { const a = BigInt(9007199254740991) const b = BigInt(9007199254740991) const c = BigInt(7007199254740991) expect(equals(a, b)).toBeTrue() expect(equals(a, c)).toBeFalse()})
describe('brute force', () => { compareCombinations({ callback : errorsCounters => { expect(errorsCounters).toMatchInlineSnapshot(`{ "ERRORS_MESSAGE_MISMATCH": 0, "ERRORS_TYPE_MISMATCH": 0, "RESULTS_MISMATCH": 0, "SHOULD_NOT_THROW": 0, "SHOULD_THROW": 0, "TOTAL_TESTS": 289,}`) }, firstInput : variousTypes, fn : equals, fnRamda : equalsRamda, secondInput : variousTypes, })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {equals} from 'rambda'
describe('R.equals', () => { it('happy', () => { const result = equals(4, 1) result // $ExpectType boolean }) it('with object', () => { const foo = {a: 1} const bar = {a: 2} const result = equals(foo, bar) result // $ExpectType boolean }) it('curried', () => { const result = equals(4)(1) result // $ExpectType boolean })})```
</details>[](#equals)
### evolve
```typescript
evolve<T, U>(rules: ((x: T) => U)[], list: T[]): U[]```
It takes object or array of functions as set of rules. These `rules` are applied to the `iterable` input to produce the result.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20rules%20%3D%20%7B%0A%20%20foo%20%3A%20add(1)%2C%0A%20%20bar%20%3A%20add(-1)%2C%0A%7D%0Aconst%20input%20%3D%20%7B%0A%20%20a%20%20%20%3A%201%2C%0A%20%20foo%20%3A%202%2C%0A%20%20bar%20%3A%203%2C%0A%7D%0Aconst%20result%20%3D%20evolve(rules%2C%20input)%0Aconst%20expected%20%3D%20%7B%0A%20%20a%20%20%20%3A%201%2C%0A%20%20foo%20%3A%203%2C%0A%20%20bar%20%3A%202%2C%0A%7D)%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.evolve</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptevolve<T, U>(rules: ((x: T) => U)[], list: T[]): U[];evolve<T, U>(rules: ((x: T) => U)[]) : (list: T[]) => U[];evolve<E extends Evolver, V extends Evolvable<E>>(rules: E, obj: V): Evolve<V, E>;evolve<E extends Evolver>(rules: E): <V extends Evolvable<E>>(obj: V) => Evolve<V, E>;```
</details><details><summary><strong>R.evolve</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'import { mapArray, mapObject } from './map.js'import { type } from './type.js'
export function evolveArray(rules, list){ return mapArray( (x, i) => { if (type(rules[ i ]) === 'Function'){ return rules[ i ](x) } return x }, list, true )}
export function evolveObject(rules, iterable){ return mapObject((x, prop) => { if (type(x) === 'Object'){ const typeRule = type(rules[ prop ]) if (typeRule === 'Function'){ return rules[ prop ](x) } if (typeRule === 'Object'){ return evolve(rules[ prop ], x) } return x } if (type(rules[ prop ]) === 'Function'){ return rules[ prop ](x) } return x }, iterable)}
export function evolve(rules, iterable){ if (arguments.length === 1){ return _iterable => evolve(rules, _iterable) } const rulesType = type(rules) const iterableType = type(iterable) if (iterableType !== rulesType){ throw new Error('iterableType !== rulesType') } if (![ 'Object', 'Array' ].includes(rulesType)){ throw new Error(`'iterable' and 'rules' are from wrong type ${ rulesType }`) } if (iterableType === 'Object'){ return evolveObject(rules, iterable) } return evolveArray(rules, iterable)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { evolve as evolveRamda } from 'ramda'
import { add } from '../rambda.js'import { compareCombinations, compareToRamda } from './_internals/testUtils.js'import { evolve } from './evolve.js'
test('happy', () => { const rules = { foo : add(1), nested : { bar : x => Object.keys(x).length }, } const input = { a : 1, foo : 2, nested : { bar : { z : 3 } }, } const result = evolve(rules, input) expect(result).toEqual({ a : 1, foo : 3, nested : { bar : 1 }, })})
test('nested rule is wrong', () => { const rules = { foo : add(1), nested : { bar : 10 }, } const input = { a : 1, foo : 2, nested : { bar : { z : 3 } }, } const result = evolve(rules)(input) expect(result).toEqual({ a : 1, foo : 3, nested : { bar : { z : 3 } }, })})
test('is recursive', () => { const rules = { nested : { second : add(-1), third : add(1), }, } const object = { first : 1, nested : { second : 2, third : 3, }, } const expected = { first : 1, nested : { second : 1, third : 4, }, } const result = evolve(rules, object) expect(result).toEqual(expected)})
test('ignores primitive values', () => { const rules = { n : 2, m : 'foo', } const object = { n : 0, m : 1, } const expected = { n : 0, m : 1, } const result = evolve(rules, object) expect(result).toEqual(expected)})
test('with array', () => { const rules = [ add(1), add(-1) ] const list = [ 100, 1400 ] const expected = [ 101, 1399 ] const result = evolve(rules, list) expect(result).toEqual(expected)})
const rulesObject = { a : add(1) }const rulesList = [ add(1) ]const possibleIterables = [ null, undefined, '', 42, [], [ 1 ], { a : 1 } ]const possibleRules = [ ...possibleIterables, rulesList, rulesObject ]
describe('brute force', () => { compareCombinations({ firstInput : possibleRules, callback : errorsCounters => { expect(errorsCounters).toMatchInlineSnapshot(` { "ERRORS_MESSAGE_MISMATCH": 0, "ERRORS_TYPE_MISMATCH": 4, "RESULTS_MISMATCH": 0, "SHOULD_NOT_THROW": 51, "SHOULD_THROW": 0, "TOTAL_TESTS": 63, } `) }, secondInput : possibleIterables, fn : evolve, fnRamda : evolveRamda, })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {evolve, add} from 'rambda'
describe('R.evolve', () => { it('happy', () => { const input = { foo: 2, nested: { a: 1, bar: 3, }, } const rules = { foo: add(1), nested: { a: add(-1), bar: add(1), }, } const result = evolve(rules, input) const curriedResult = evolve(rules)(input) result.nested.a // $ExpectType number curriedResult.nested.a // $ExpectType number result.nested.bar // $ExpectType number result.foo // $ExpectType number }) it('with array', () => { const rules = [String, String] const input = [100, 1400] const result = evolve(rules, input) const curriedResult = evolve(rules)(input) result // $ExpectType string[] curriedResult // $ExpectType string[] })})```
</details>[](#evolve)
### F
```typescript
F(): boolean```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20F()%20%2F%2F%20%3D%3E%20false">Try this <strong>R.F</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptF(): boolean;```
</details><details><summary><strong>R.F</strong> source</summary>```javascriptexport function F(){ return false}```
</details>[](#F)
### filter
```typescript
filter<T>(predicate: Predicate<T>): (input: T[]) => T[]```
It filters list or object `input` using a `predicate` function.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B3%2C%204%2C%203%2C%202%5D%0Aconst%20listPredicate%20%3D%20x%20%3D%3E%20x%20%3E%202%0A%0Aconst%20object%20%3D%20%7Babc%3A%20'fo'%2C%20xyz%3A%20'bar'%2C%20baz%3A%20'foo'%7D%0Aconst%20objectPredicate%20%3D%20(x%2C%20prop)%20%3D%3E%20x.length%20%2B%20prop.length%20%3E%205%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.filter(listPredicate%2C%20list)%2C%0A%20%20R.filter(objectPredicate%2C%20object)%0A%5D%0A%2F%2F%20%3D%3E%20%5B%20%5B3%2C%204%5D%2C%20%7B%20xyz%3A%20'bar'%2C%20baz%3A%20'foo'%7D%20%5D">Try this <strong>R.filter</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptfilter<T>(predicate: Predicate<T>): (input: T[]) => T[];filter<T>(predicate: Predicate<T>, input: T[]): T[];filter<T, U>(predicate: ObjectPredicate<T>): (x: Dictionary<T>) => Dictionary<T>;filter<T>(predicate: ObjectPredicate<T>, x: Dictionary<T>): Dictionary<T>;```
</details><details><summary><strong>R.filter</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'
export function filterObject(predicate, obj){ const willReturn = {} for (const prop in obj){ if (predicate( obj[ prop ], prop, obj )){ willReturn[ prop ] = obj[ prop ] } } return willReturn}
export function filterArray( predicate, list, indexed = false){ let index = 0 const len = list.length const willReturn = [] while (index < len){ const predicateResult = indexed ? predicate(list[ index ], index) : predicate(list[ index ]) if (predicateResult){ willReturn.push(list[ index ]) } index++ } return willReturn}
export function filter(predicate, iterable){ if (arguments.length === 1) return _iterable => filter(predicate, _iterable) if (!iterable){ throw new Error('Incorrect iterable input') } if (isArray(iterable)) return filterArray( predicate, iterable, false ) return filterObject(predicate, iterable)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { filter as filterRamda } from 'ramda'
import { filter } from './filter.js'import { T } from './T.js'
const sampleObject = { a : 1, b : 2, c : 3, d : 4,}
test('happy', () => { const isEven = n => n % 2 === 0 expect(filter(isEven, [ 1, 2, 3, 4 ])).toEqual([ 2, 4 ]) expect(filter(isEven, { a : 1, b : 2, d : 3, })).toEqual({ b : 2 })})
test('predicate when input is object', () => { const obj = { a : 1, b : 2, } const predicate = ( val, prop, inputObject ) => { expect(inputObject).toEqual(obj) expect(typeof prop).toBe('string') return val < 2 } expect(filter(predicate, obj)).toEqual({ a : 1 })})
test('with object', () => { const isEven = n => n % 2 === 0 const result = filter(isEven, sampleObject) const expectedResult = { b : 2, d : 4, } expect(result).toEqual(expectedResult)})
test('bad inputs difference between Ramda and Rambda', () => { expect(() => filter(T, null)).toThrowWithMessage(Error, 'Incorrect iterable input') expect(() => filter(T)(undefined)).toThrowWithMessage(Error, 'Incorrect iterable input') expect(() => filterRamda(T, null)).toThrowWithMessage(TypeError, 'Cannot read properties of null (reading \'fantasy-land/filter\')') expect(() => filterRamda(T, undefined)).toThrowWithMessage(TypeError, 'Cannot read properties of undefined (reading \'fantasy-land/filter\')')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {filter} from 'rambda'
const list = [1, 2, 3]const obj = {a: 1, b: 2}
describe('R.filter with array', () => { it('happy', () => { const result = filter<number>(x => { x // $ExpectType number return x > 1 }, list) result // $ExpectType number[] }) it('curried', () => { const result = filter<number>(x => { x // $ExpectType number return x > 1 })(list) result // $ExpectType number[] })})
describe('R.filter with objects', () => { it('happy', () => { const result = filter<number>((val, prop, origin) => { val // $ExpectType number prop // $ExpectType string origin // $ExpectType Dictionary<number> return val > 1 }, obj) result // $ExpectType Dictionary<number> }) it('curried version requires second dummy type', () => { const result = filter<number, any>((val, prop, origin) => { val // $ExpectType number prop // $ExpectType string origin // $ExpectType Dictionary<number> return val > 1 })(obj) result // $ExpectType Dictionary<number> })})```
</details>[](#filter)
### find
```typescript
find<T>(predicate: (x: T) => boolean, list: T[]): T | undefined```
It returns the first element of `list` that satisfy the `predicate`.
If there is no such element, it returns `undefined`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20x%20%3D%3E%20R.type(x.foo)%20%3D%3D%3D%20'Number'%0Aconst%20list%20%3D%20%5B%7Bfoo%3A%20'bar'%7D%2C%20%7Bfoo%3A%201%7D%5D%0A%0Aconst%20result%20%3D%20R.find(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20%7Bfoo%3A%201%7D">Try this <strong>R.find</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptfind<T>(predicate: (x: T) => boolean, list: T[]): T | undefined;find<T>(predicate: (x: T) => boolean): (list: T[]) => T | undefined;```
</details><details><summary><strong>R.find</strong> source</summary>```javascriptexport function find(predicate, list){ if (arguments.length === 1) return _list => find(predicate, _list) let index = 0 const len = list.length while (index < len){ const x = list[ index ] if (predicate(x)){ return x } index++ }}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { find } from './find.js'import { propEq } from './propEq.js'
const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]
test('happy', () => { const fn = propEq(2, 'a') expect(find(fn, list)).toEqual({ a : 2 })})
test('with curry', () => { const fn = propEq(4, 'a') expect(find(fn)(list)).toBeUndefined()})
test('with empty list', () => { expect(find(() => true, [])).toBeUndefined()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {find} from 'rambda'
const list = [1, 2, 3]
describe('R.find', () => { it('happy', () => { const predicate = (x: number) => x > 2 const result = find(predicate, list) result // $ExpectType number | undefined }) it('curried', () => { const predicate = (x: number) => x > 2 const result = find(predicate)(list) result // $ExpectType number | undefined })})```
</details>[](#find)
### findIndex
```typescript
findIndex<T>(predicate: (x: T) => boolean, list: T[]): number```
It returns the index of the first element of `list` satisfying the `predicate` function.
If there is no such element, then `-1` is returned.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20x%20%3D%3E%20R.type(x.foo)%20%3D%3D%3D%20'Number'%0Aconst%20list%20%3D%20%5B%7Bfoo%3A%20'bar'%7D%2C%20%7Bfoo%3A%201%7D%5D%0A%0Aconst%20result%20%3D%20R.findIndex(predicate%2C%20list)%0A%2F%2F%20%3D%3E%201">Try this <strong>R.findIndex</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptfindIndex<T>(predicate: (x: T) => boolean, list: T[]): number;findIndex<T>(predicate: (x: T) => boolean): (list: T[]) => number;```
</details><details><summary><strong>R.findIndex</strong> source</summary>```javascriptexport function findIndex(predicate, list){ if (arguments.length === 1) return _list => findIndex(predicate, _list) const len = list.length let index = -1 while (++index < len){ if (predicate(list[ index ])){ return index } } return -1}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { findIndex } from './findIndex.js'import { propEq } from './propEq.js'
const list = [ { a : 1 }, { a : 2 }, { a : 3 } ]
test('happy', () => { expect(findIndex(propEq(2, 'a'), list)).toBe(1) expect(findIndex(propEq(1, 'a'))(list)).toBe(0) expect(findIndex(propEq(4, 'a'))(list)).toBe(-1)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {findIndex} from 'rambda'
const list = [1, 2, 3]
describe('R.findIndex', () => { it('happy', () => { const predicate = (x: number) => x > 2 const result = findIndex(predicate, list) result // $ExpectType number }) it('curried', () => { const predicate = (x: number) => x > 2 const result = findIndex(predicate)(list) result // $ExpectType number })})```
</details>[](#findIndex)
### findLast
```typescript
findLast<T>(fn: (x: T) => boolean, list: T[]): T | undefined```
It returns the last element of `list` satisfying the `predicate` function.
If there is no such element, then `undefined` is returned.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20x%20%3D%3E%20R.type(x.foo)%20%3D%3D%3D%20'Number'%0Aconst%20list%20%3D%20%5B%7Bfoo%3A%200%7D%2C%20%7Bfoo%3A%201%7D%5D%0A%0Aconst%20result%20%3D%20R.findLast(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20%7Bfoo%3A%201%7D">Try this <strong>R.findLast</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptfindLast<T>(fn: (x: T) => boolean, list: T[]): T | undefined;findLast<T>(fn: (x: T) => boolean): (list: T[]) => T | undefined;```
</details><details><summary><strong>R.findLast</strong> source</summary>```javascriptexport function findLast(predicate, list){ if (arguments.length === 1) return _list => findLast(predicate, _list) let index = list.length while (--index >= 0){ if (predicate(list[ index ])){ return list[ index ] } } return undefined}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { findLast } from './findLast.js'
test('happy', () => { const result = findLast(x => x > 1, [ 1, 1, 1, 2, 3, 4, 1 ]) expect(result).toBe(4) expect(findLast(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toBe(0)})
test('with curry', () => { expect(findLast(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toBe(4)})
const obj1 = { x : 100 }const obj2 = { x : 200 }const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]const even = function (x){ return x % 2 === 0}const gt100 = function (x){ return x > 100}const isStr = function (x){ return typeof x === 'string'}const xGt100 = function (o){ return o && o.x > 100}
test('ramda 1', () => { expect(findLast(even, a)).toBe(0) expect(findLast(gt100, a)).toBe(300) expect(findLast(isStr, a)).toBe('cow') expect(findLast(xGt100, a)).toEqual(obj2)})
test('ramda 2', () => { expect(findLast(even, [ 'zing' ])).toBeUndefined()})
test('ramda 3', () => { expect(findLast(even, [ 2, 3, 5 ])).toBe(2)})
test('ramda 4', () => { expect(findLast(even, [])).toBeUndefined()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {findLast} from 'rambda'
const list = [1, 2, 3]
describe('R.findLast', () => { it('happy', () => { const predicate = (x: number) => x > 2 const result = findLast(predicate, list) result // $ExpectType number | undefined }) it('curried', () => { const predicate = (x: number) => x > 2 const result = findLast(predicate)(list) result // $ExpectType number | undefined })})```
</details>[](#findLast)
### findLastIndex
```typescript
findLastIndex<T>(predicate: (x: T) => boolean, list: T[]): number```
It returns the index of the last element of `list` satisfying the `predicate` function.
If there is no such element, then `-1` is returned.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20x%20%3D%3E%20R.type(x.foo)%20%3D%3D%3D%20'Number'%0Aconst%20list%20%3D%20%5B%7Bfoo%3A%200%7D%2C%20%7Bfoo%3A%201%7D%5D%0A%0Aconst%20result%20%3D%20R.findLastIndex(predicate%2C%20list)%0A%2F%2F%20%3D%3E%201">Try this <strong>R.findLastIndex</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptfindLastIndex<T>(predicate: (x: T) => boolean, list: T[]): number;findLastIndex<T>(predicate: (x: T) => boolean): (list: T[]) => number;```
</details><details><summary><strong>R.findLastIndex</strong> source</summary>```javascriptexport function findLastIndex(fn, list){ if (arguments.length === 1) return _list => findLastIndex(fn, _list) let index = list.length while (--index >= 0){ if (fn(list[ index ])){ return index } } return -1}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { findLastIndex } from './findLastIndex.js'
test('happy', () => { const result = findLastIndex(x => x > 1, [ 1, 1, 1, 2, 3, 4, 1 ]) expect(result).toBe(5) expect(findLastIndex(x => x === 0, [ 0, 1, 1, 2, 3, 4, 1 ])).toBe(0)})
test('with curry', () => { expect(findLastIndex(x => x > 1)([ 1, 1, 1, 2, 3, 4, 1 ])).toBe(5)})
const obj1 = { x : 100 }const obj2 = { x : 200 }const a = [ 11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0 ]const even = function (x){ return x % 2 === 0}const gt100 = function (x){ return x > 100}const isStr = function (x){ return typeof x === 'string'}const xGt100 = function (o){ return o && o.x > 100}
test('ramda 1', () => { expect(findLastIndex(even, a)).toBe(15) expect(findLastIndex(gt100, a)).toBe(9) expect(findLastIndex(isStr, a)).toBe(3) expect(findLastIndex(xGt100, a)).toBe(10)})
test('ramda 2', () => { expect(findLastIndex(even, [ 'zing' ])).toBe(-1)})
test('ramda 3', () => { expect(findLastIndex(even, [ 2, 3, 5 ])).toBe(0)})
test('ramda 4', () => { expect(findLastIndex(even, [])).toBe(-1)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {findLastIndex} from 'rambda'
const list = [1, 2, 3]
describe('R.findLastIndex', () => { it('happy', () => { const predicate = (x: number) => x > 2 const result = findLastIndex(predicate, list) result // $ExpectType number }) it('curried', () => { const predicate = (x: number) => x > 2 const result = findLastIndex(predicate)(list) result // $ExpectType number })})```
</details>[](#findLastIndex)
### flatten
```typescript
flatten<T>(list: any[]): T[]```
It deeply flattens an array.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.flatten(%5B%0A%20%201%2C%20%0A%20%202%2C%20%0A%20%20%5B3%2C%2030%2C%20%5B300%5D%5D%2C%20%0A%20%20%5B4%5D%0A%5D)%0A%2F%2F%20%3D%3E%20%5B%201%2C%202%2C%203%2C%2030%2C%20300%2C%204%20%5D">Try this <strong>R.flatten</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptflatten<T>(list: any[]): T[];```
</details><details><summary><strong>R.flatten</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'
export function flatten(list, input){ const willReturn = input === undefined ? [] : input for (let i = 0; i < list.length; i++){ if (isArray(list[ i ])){ flatten(list[ i ], willReturn) } else { willReturn.push(list[ i ]) } } return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { flatten } from './flatten.js'
test('happy', () => { expect(flatten([ 1, 2, 3, [ [ [ [ [ 4 ] ] ] ] ] ])).toEqual([ 1, 2, 3, 4 ]) expect(flatten([ 1, [ 2, [ [ 3 ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ]) expect(flatten([ 1, [ 2, [ [ [ 3 ] ] ] ], [ 4 ] ])).toEqual([ 1, 2, 3, 4 ]) expect(flatten([ 1, 2, [ 3, 4 ], 5, [ 6, [ 7, 8, [ 9, [ 10, 11 ], 12 ] ] ] ])).toEqual([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 ])})
test('readme example', () => { const result = flatten([ 1, 2, [ 3, 30, [ 300 ] ], [ 4 ] ]) expect(result).toEqual([ 1, 2, 3, 30, 300, 4 ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {flatten} from 'rambda'
describe('flatten', () => { it('happy', () => { const result = flatten<number>([1, 2, [3, [4]]]) result // $ExpectType number[] })})```
</details>[](#flatten)
### flip
It returns function which calls `fn` with exchanged first and second argument.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20subtractFlip%20%3D%20R.flip(R.subtract)%0A%0Aconst%20result%20%3D%20%5B%0A%20%20subtractFlip(1%2C7)%2C%0A%20%20R.subtract(1%2C%206)%0A%5D%20%20%0A%2F%2F%20%3D%3E%20%5B6%2C%20-6%5D">Try this <strong>R.flip</strong> example in Rambda REPL</a>[](#flip)
### forEach
```typescript
forEach<T>(fn: Iterator<T, void>, list: T[]): T[]```
It applies `iterable` function over all members of `list` and returns `list`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20sideEffect%20%3D%20%7B%7D%0Aconst%20result%20%3D%20R.forEach(%0A%20%20x%20%3D%3E%20sideEffect%5B%60foo%24%7Bx%7D%60%5D%20%3D%20x%0A)(%5B1%2C%202%5D)%0A%0AsideEffect%20%2F%2F%20%3D%3E%20%7Bfoo1%3A%201%2C%20foo2%3A%202%7D%0Aresult%20%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.forEach</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptforEach<T>(fn: Iterator<T, void>, list: T[]): T[];forEach<T>(fn: Iterator<T, void>): (list: T[]) => T[];forEach<T>(fn: ObjectIterator<T, void>, list: Dictionary<T>): Dictionary<T>;forEach<T, U>(fn: ObjectIterator<T, void>): (list: Dictionary<T>) => Dictionary<T>;```
</details><details><summary><strong>R.forEach</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'import { forEachObjIndexedFn } from './forEachObjIndexed.js'
export function forEach(fn, iterable){ if (arguments.length === 1) return _list => forEach(fn, _list) if (iterable === undefined) return if (isArray(iterable)){ let index = 0 const len = iterable.length while (index < len){ fn(iterable[ index ]) index++ } } else return forEachObjIndexedFn(fn, iterable) return iterable}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { forEach } from './forEach.js'import { type } from './type.js'
test('happy', () => { const sideEffect = {} forEach(x => sideEffect[ `foo${ x }` ] = x + 10)([ 1, 2 ]) expect(sideEffect).toEqual({ foo1 : 11, foo2 : 12, })})
test('iterate over object', () => { const obj = { a : 1, b : [ 1, 2 ], c : { d : 7 }, f : 'foo', } const result = {} const returned = forEach(( val, prop, inputObj ) => { expect(type(inputObj)).toBe('Object') result[ prop ] = `${ prop }-${ type(val) }` })(obj) const expected = { a : 'a-Number', b : 'b-Array', c : 'c-Object', f : 'f-String', } expect(result).toEqual(expected) expect(returned).toEqual(obj)})
test('with empty list', () => { const list = [] const result = forEach(x => x * x)(list) expect(result).toEqual(list)})
test('with wrong input', () => { const list = undefined const result = forEach(x => x * x)(list) expect(result).toBeUndefined()})
test('returns the input', () => { const list = [ 1, 2, 3 ] const result = forEach(x => x * x)(list) expect(result).toEqual(list)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {forEach} from 'rambda'
const list = [1, 2, 3]const obj = {a: 1, b: 2}
describe('R.forEach with arrays', () => { it('happy', () => { const result = forEach(a => { a // $ExpectType number }, list) result // $ExpectType number[] }) it('curried require an explicit typing', () => { const result = forEach<number>(a => { a // $ExpectType number })(list) result // $ExpectType number[] })})
describe('R.forEach with objects', () => { it('happy', () => { const result = forEach((a, b, c) => { a // $ExpectType number b // $ExpectType string c // $ExpectType Dictionary<number> return `${a}` }, obj) result // $ExpectType Dictionary<number> }) it('curried require an input typing and a dummy third typing', () => { // Required in order all typings to work const result = forEach<number, any>((a, b, c) => { a // $ExpectType number b // $ExpectType string c // $ExpectType Dictionary<number> })(obj) result // $ExpectType Dictionary<number> }) it('iterator without property', () => { const result = forEach(a => { a // $ExpectType number }, obj) result // $ExpectType Dictionary<number> })})```
</details>[](#forEach)
### forEachObjIndexed
[](#forEachObjIndexed)
### fromPairs
It transforms a `listOfPairs` to an object.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20listOfPairs%20%3D%20%5B%20%5B%20'a'%2C%201%20%5D%2C%20%5B%20'b'%2C%202%20%5D%2C%20%5B%20'c'%2C%20%5B%203%2C%204%20%5D%20%5D%20%5D%0Aconst%20expected%20%3D%20%7B%0A%20%20a%20%3A%201%2C%0A%20%20b%20%3A%202%2C%0A%20%20c%20%3A%20%5B%203%2C%204%20%5D%2C%0A%7D%0A%0Aconst%20result%20%3D%20R.fromPairs(listOfPairs)%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.fromPairs</strong> example in Rambda REPL</a>[](#fromPairs)
### groupBy
It splits `list` according to a provided `groupFn` function and returns an object.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%20'a'%2C%20'b'%2C%20'aa'%2C%20'bb'%20%5D%0Aconst%20groupFn%20%3D%20x%20%3D%3E%20x.length%0A%0Aconst%20result%20%3D%20R.groupBy(groupFn%2C%20list)%0A%2F%2F%20%3D%3E%20%7B%20'1'%3A%20%5B'a'%2C%20'b'%5D%2C%20'2'%3A%20%5B'aa'%2C%20'bb'%5D%20%7D">Try this <strong>R.groupBy</strong> example in Rambda REPL</a>[](#groupBy)
### groupWith
It returns separated version of list or string `input`, where separation is done with equality `compareFn` function.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20compareFn%20%3D%20(x%2C%20y)%20%3D%3E%20x%20%3D%3D%3D%20y%0Aconst%20list%20%3D%20%5B1%2C%202%2C%202%2C%201%2C%201%2C%202%5D%0A%0Aconst%20result%20%3D%20R.groupWith(isConsecutive%2C%20list)%0A%2F%2F%20%3D%3E%20%5B%5B1%5D%2C%20%5B2%2C2%5D%2C%20%5B1%2C1%5D%2C%20%5B2%5D%5D">Try this <strong>R.groupWith</strong> example in Rambda REPL</a>[](#groupWith)
### gt
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5BR.gt(2%2C%201)%2C%20R.gt(2%2C%203)%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.gt</strong> example in Rambda REPL</a>[](#gt)
### gte
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5BR.gte(2%2C%201)%2C%20R.gte(2%2C%202)%2C%20R.gte(2%2C%203)%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%2C%20false%5D">Try this <strong>R.gte</strong> example in Rambda REPL</a>[](#gte)
### has
```typescript
has<T>(prop: string, obj: T): boolean```
It returns `true` if `obj` has property `prop`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%201%7D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.has('a'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.has('b'%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.has</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripthas<T>(prop: string, obj: T): boolean;has(prop: string): <T>(obj: T) => boolean;```
</details><details><summary><strong>R.has</strong> source</summary>```javascriptexport function has(prop, obj){ if (arguments.length === 1) return _obj => has(prop, _obj) if (!obj) return false return obj.hasOwnProperty(prop)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { has } from './has.js'
test('happy', () => { expect(has('a')({ a : 1 })).toBeTrue() expect(has('b', { a : 1 })).toBeFalse()})
test('with non-object', () => { expect(has('a', undefined)).toBeFalse() expect(has('a', null)).toBeFalse() expect(has('a', true)).toBeFalse() expect(has('a', '')).toBeFalse() expect(has('a', /a/)).toBeFalse()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {has} from 'rambda'
describe('R.has', () => { it('happy', () => { const result = has('foo', {a: 1}) const curriedResult = has('bar')({a: 1}) result // $ExpectType boolean curriedResult // $ExpectType boolean })})```
</details>[](#has)
### hasIn
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.hasIn('a'%2C%20%7Ba%3A%201%7D)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.hasIn</strong> example in Rambda REPL</a>[](#hasIn)
### hasPath
```typescript
hasPath<T>( path: string | string[], input: object): boolean```
It will return true, if `input` object has truthy `path`(calculated with `R.path`).
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20path%20%3D%20'a.b'%0Aconst%20pathAsArray%20%3D%20%5B'a'%2C%20'b'%5D%0Aconst%20obj%20%3D%20%7Ba%3A%20%7Bb%3A%20%5B%5D%7D%7D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.hasPath(path%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.hasPath(pathAsArray%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.hasPath('a.c'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%2C%20false%5D">Try this <strong>R.hasPath</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripthasPath<T>( path: string | string[], input: object): boolean;hasPath<T>( path: string | string[]): (input: object) => boolean;```
</details><details><summary><strong>R.hasPath</strong> source</summary>```javascriptimport { path } from './path.js'
export function hasPath(pathInput, obj){ if (arguments.length === 1){ return objHolder => hasPath(pathInput, objHolder) } return path(pathInput, obj) !== undefined}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { hasPath } from './hasPath.js'
test('when true', () => { const path = 'a.b' const obj = { a : { b : [] } } const result = hasPath(path)(obj) const expectedResult = true expect(result).toEqual(expectedResult)})
test('when false', () => { const path = 'a.b' const obj = {} const result = hasPath(path, obj) const expectedResult = false expect(result).toEqual(expectedResult)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {hasPath} from 'rambda'
describe('R.hasPath', () => { it('string path', () => { const obj = {a: {b: 1}} const result = hasPath('a.b', obj) const curriedResult = hasPath('a.c')(obj) result // $ExpectType boolean curriedResult // $ExpectType boolean }) it('array path', () => { const obj = {a: {b: 1}} const result = hasPath(['a', 'b'], obj) const curriedResult = hasPath(['a', 'c'])(obj) result // $ExpectType boolean curriedResult // $ExpectType boolean })})```
</details>[](#hasPath)
### head
```typescript
head(str: string): string```
It returns the first element of list or string `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.head(%5B1%2C%202%2C%203%5D)%2C%0A%20%20R.head('foo')%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B1%2C%20'f'%5D">Try this <strong>R.head</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripthead(str: string): string;head(str: ''): undefined;head<T>(list: never[]): undefined;head<T extends unknown[]>(array: T): FirstArrayElement<T>head<T extends readonly unknown[]>(array: T): FirstArrayElement<T>```
</details><details><summary><strong>R.head</strong> source</summary>```javascriptexport function head(listOrString){ if (typeof listOrString === 'string') return listOrString[ 0 ] || '' return listOrString[ 0 ]}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { head } from './head.js'
test('head', () => { expect(head([ 'fi', 'fo', 'fum' ])).toBe('fi') expect(head([])).toBeUndefined() expect(head('foo')).toBe('f') expect(head('')).toBe('')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport { emptyList, emptyString, mixedList, mixedListConst, numberList, numberListConst, string,} from '_internals/typescriptTestUtils'import {head, last} from 'rambda'
describe('R.head', () => { it('string', () => { head(string) // $ExpectType string last(string) // $ExpectType string }) it('empty string', () => { head(emptyString) // $ExpectType undefined last(emptyString) // $ExpectType undefined }) it('array', () => { head(numberList) // $ExpectType number head(numberListConst) // $ExpectType 1 last(numberList) // $ExpectType number last(numberListConst) // $ExpectType 3 }) it('empty array', () => { const list = [] as const head(emptyList) // $ExpectType undefined head(list) // $ExpectType never last(emptyList) // $ExpectType undefined last(list) // $ExpectType never }) it('mixed', () => { head(mixedList) // $ExpectType string | number head(mixedListConst) // $ExpectType 1 last(mixedList) // $ExpectType string | number last(mixedListConst) // $ExpectType "bar" })})```
</details>[](#head)
### identical
It returns `true` if its arguments `a` and `b` are identical.
Otherwise, it returns `false`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20objA%20%3D%20%7Ba%3A%201%7D%3B%0Aconst%20objB%20%3D%20%7Ba%3A%201%7D%3B%0AR.identical(objA%2C%20objA)%3B%20%2F%2F%20%3D%3E%20true%0AR.identical(objA%2C%20objB)%3B%20%2F%2F%20%3D%3E%20false%0AR.identical(1%2C%201)%3B%20%2F%2F%20%3D%3E%20true%0AR.identical(1%2C%20'1')%3B%20%2F%2F%20%3D%3E%20false%0AR.identical(%5B%5D%2C%20%5B%5D)%3B%20%2F%2F%20%3D%3E%20false%0AR.identical(0%2C%20-0)%3B%20%2F%2F%20%3D%3E%20false%0Aconst%20result%20%3D%20R.identical(NaN%2C%20NaN)%3B%20%2F%2F%20%3D%3E%20true">Try this <strong>R.identical</strong> example in Rambda REPL</a>[](#identical)
### identity
```typescript
identity<T>(input: T): T```
It just passes back the supplied `input` argument.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.identity(7)%20%2F%2F%20%3D%3E%207">Try this <strong>R.identity</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptidentity<T>(input: T): T;```
</details><details><summary><strong>R.identity</strong> source</summary>```javascriptexport function identity(x){ return x}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { identity } from './identity.js'
test('happy', () => { expect(identity(7)).toBe(7) expect(identity(true)).toBeTrue() expect(identity({ a : 1 })).toEqual({ a : 1 })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {identity} from 'rambda'
describe('R.identity', () => { it('happy', () => { const result = identity(4) result // $ExpectType 4 })})```
</details>[](#identity)
### ifElse
```typescript
ifElse<T, TFiltered extends T, TOnTrueResult, TOnFalseResult>( pred: (a: T) => a is TFiltered, onTrue: (a: TFiltered) => TOnTrueResult, onFalse: (a: Exclude<T, TFiltered>) => TOnFalseResult,): (a: T) => TOnTrueResult | TOnFalseResult```
It expects `condition`, `onTrue` and `onFalse` functions as inputs and it returns a new function with example name of `fn`.
When `fn`` is called with `input` argument, it will return either `onTrue(input)` or `onFalse(input)` depending on `condition(input)` evaluation.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20R.ifElse(%0A%20x%20%3D%3E%20x%3E10%2C%0A%20x%20%3D%3E%20x*2%2C%0A%20x%20%3D%3E%20x*10%0A)%0A%0Aconst%20result%20%3D%20%5B%20fn(8)%2C%20fn(18)%20%5D%0A%2F%2F%20%3D%3E%20%5B80%2C%2036%5D">Try this <strong>R.ifElse</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptifElse<T, TFiltered extends T, TOnTrueResult, TOnFalseResult>( pred: (a: T) => a is TFiltered, onTrue: (a: TFiltered) => TOnTrueResult, onFalse: (a: Exclude<T, TFiltered>) => TOnFalseResult,): (a: T) => TOnTrueResult | TOnFalseResult;ifElse<TArgs extends any[], TOnTrueResult, TOnFalseResult>(fn: (...args: TArgs) => boolean, onTrue: (...args: TArgs) => TOnTrueResult, onFalse: (...args: TArgs) => TOnFalseResult): (...args: TArgs) => TOnTrueResult | TOnFalseResult;```
</details><details><summary><strong>R.ifElse</strong> source</summary>```javascriptimport { curry } from './curry.js'
function ifElseFn( condition, onTrue, onFalse){ return (...input) => { const conditionResult = typeof condition === 'boolean' ? condition : condition(...input) if (conditionResult === true){ return onTrue(...input) } return onFalse(...input) }}
export const ifElse = curry(ifElseFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { always } from './always.js'import { has } from './has.js'import { identity } from './identity.js'import { ifElse } from './ifElse.js'import { prop } from './prop.js'
const condition = has('foo')const v = function (a){ return typeof a === 'number'}const t = function (a){ return a + 1}const ifFn = x => prop('foo', x).lengthconst elseFn = () => false
test('happy', () => { const fn = ifElse(condition, ifFn)(elseFn) expect(fn({ foo : 'bar' })).toBe(3) expect(fn({ fo : 'bar' })).toBeFalse()})
test('ramda spec', () => { const ifIsNumber = ifElse(v) expect(ifIsNumber(t, identity)(15)).toBe(16) expect(ifIsNumber(t, identity)('hello')).toBe('hello')})
test('pass all arguments', () => { const identity = function (a){ return a } const v = function (){ return true } const onTrue = function (a, b){ expect(a).toBe(123) expect(b).toBe('abc') } ifElse( v, onTrue, identity )(123, 'abc')})
test('accept constant as condition', () => { const fn = ifElse(true)(always(true))(always(false)) expect(fn()).toBeTrue()})
test('accept constant as condition - case 2', () => { const fn = ifElse( false, always(true), always(false) ) expect(fn()).toBeFalse()})
test('curry 1', () => { const fn = ifElse(condition, ifFn)(elseFn) expect(fn({ foo : 'bar' })).toBe(3) expect(fn({ fo : 'bar' })).toBeFalse()})
test('curry 2', () => { const fn = ifElse(condition)(ifFn)(elseFn) expect(fn({ foo : 'bar' })).toBe(3) expect(fn({ fo : 'bar' })).toBeFalse()})
test('simple arity of 1', () => { const condition = x => x > 5 const onTrue = x => x + 1 const onFalse = x => x + 10 const result = ifElse( condition, onTrue, onFalse )(1) expect(result).toBe(11)})
test('simple arity of 2', () => { const condition = (x, y) => x + y > 5 const onTrue = (x, y) => x + y + 1 const onFalse = (x, y) => x + y + 10 const result = ifElse( condition, onTrue, onFalse )(1, 10) expect(result).toBe(12)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {ifElse} from 'rambda'
describe('R.ifElse', () => { it('happy', () => { const condition = (x: number) => x > 5 const onTrue = (x: number) => `foo${x}` const onFalse = (x: number) => `bar${x}` const fn = ifElse(condition, onTrue, onFalse) fn // $ExpectType (x: number) => string const result = fn(3) result // $ExpectType string }) it('arity of 2', () => { const condition = (x: number, y: string) => x + y.length > 5 const onTrue = (x: number, y: string) => `foo${x}-${y}` const onFalse = (x: number, y: string) => `bar${x}-${y}` const fn = ifElse(condition, onTrue, onFalse) fn // $ExpectType (x: number, y: string) => string const result = fn(3, 'hello') result // $ExpectType string }) test('DefinitelyTyped#59291', () => { const getLengthIfStringElseDouble = ifElse( (a: string | number): a is string => true, a => a.length, a => a * 2 ) getLengthIfStringElseDouble('foo') // $ExpectType number getLengthIfStringElseDouble(3) // $ExpectType number const result = ifElse( (a: { foo?: string, bar: number | string, }): a is {foo: string, bar: string} => true, (a): [string, string] => [a.foo, a.bar], (a): [string | undefined, string | number] => [a.foo, a.bar] ) result // $ExpectType (a: { foo?: string | undefined; bar: string | number; }) => [string, string] | [string | undefined, string | number] })})```
</details>[](#ifElse)
### inc
It increments a number.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.inc(1)%20%2F%2F%20%3D%3E%202">Try this <strong>R.inc</strong> example in Rambda REPL</a>[](#inc)
### includes
```typescript
includes<T extends string>(valueToFind: T, input: string): boolean```
If `input` is string, then this method work as native `String.includes`.
If `input` is array, then `R.equals` is used to define if `valueToFind` belongs to the list.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.includes('oo'%2C%20'foo')%2C%0A%20%20R.includes(%7Ba%3A%201%7D%2C%20%5B%7Ba%3A%201%7D%5D)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%20%5D">Try this <strong>R.includes</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptincludes<T extends string>(valueToFind: T, input: string): boolean;includes<T extends string>(valueToFind: T): (input: string) => boolean;includes<T>(valueToFind: T, input: T[]): boolean;includes<T>(valueToFind: T): (input: T[]) => boolean;```
</details><details><summary><strong>R.includes</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'import { _indexOf } from './equals.js'
export function includes(valueToFind, iterable){ if (arguments.length === 1) return _iterable => includes(valueToFind, _iterable) if (typeof iterable === 'string'){ return iterable.includes(valueToFind) } if (!iterable){ throw new TypeError(`Cannot read property \'indexOf\' of ${ iterable }`) } if (!isArray(iterable)) return false return _indexOf(valueToFind, iterable) > -1}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { includes as includesRamda } from 'ramda'
import { includes } from './includes.js'
test('with string as iterable', () => { const str = 'foo bar' expect(includes('bar')(str)).toBeTrue() expect(includesRamda('bar')(str)).toBeTrue() expect(includes('never', str)).toBeFalse() expect(includesRamda('never', str)).toBeFalse()})
test('with array as iterable', () => { const arr = [ 1, 2, 3 ] expect(includes(2)(arr)).toBeTrue() expect(includesRamda(2)(arr)).toBeTrue() expect(includes(4, arr)).toBeFalse() expect(includesRamda(4, arr)).toBeFalse()})
test('with list of objects as iterable', () => { const arr = [ { a : 1 }, { b : 2 }, { c : 3 } ] expect(includes({ c : 3 }, arr)).toBeTrue() expect(includesRamda({ c : 3 }, arr)).toBeTrue()})
test('with NaN', () => { const result = includes(NaN, [ NaN ]) const ramdaResult = includesRamda(NaN, [ NaN ]) expect(result).toBeTrue() expect(ramdaResult).toBeTrue()})
test('with wrong input that does not throw', () => { const result = includes(1, /foo/g) const ramdaResult = includesRamda(1, /foo/g) expect(result).toBeFalse() expect(ramdaResult).toBeFalse()})
test('throws on wrong input - match ramda behaviour', () => { expect(() => includes(2, null)).toThrowWithMessage(TypeError, 'Cannot read property \'indexOf\' of null') expect(() => includesRamda(2, null)).toThrowWithMessage(TypeError, 'Cannot read properties of null (reading \'indexOf\')') expect(() => includes(2, undefined)).toThrowWithMessage(TypeError, 'Cannot read property \'indexOf\' of undefined') expect(() => includesRamda(2, undefined)).toThrowWithMessage(TypeError, 'Cannot read properties of undefined (reading \'indexOf\')')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {includes} from 'rambda'
const list = [{a: {b: '1'}}, {a: {c: '2'}}, {a: {b: '3'}}]
describe('R.includes', () => { it('happy', () => { const result = includes({a: {b: '1'}}, list) result // $ExpectType boolean const result2 = includes('oo', ['f', 'oo']) result2 // $ExpectType boolean }) it('with string', () => { const str = 'foo' as 'foo' | 'bar' const result = includes('oo', str) const curriedResult = includes('oo')(str) result // $ExpectType boolean curriedResult // $ExpectType boolean })})```
</details>[](#includes)
### indexBy
It generates object with properties provided by `condition` and values provided by `list` array.
If `condition` is a function, then all list members are passed through it.
If `condition` is a string, then all list members are passed through `R.path(condition)`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%20%7Bid%3A%2010%7D%2C%20%7Bid%3A%2020%7D%20%5D%0A%0Aconst%20withFunction%20%3D%20R.indexBy(%0A%20%20x%20%3D%3E%20x.id%2C%0A%20%20list%0A)%0Aconst%20withString%20%3D%20R.indexBy(%0A%20%20'id'%2C%0A%20%20list%0A)%0Aconst%20result%20%3D%20%5B%0A%20%20withFunction%2C%20%0A%20%20R.equals(withFunction%2C%20withString)%0A%5D%0A%2F%2F%20%3D%3E%20%5B%20%7B%2010%3A%20%7Bid%3A%2010%7D%2C%2020%3A%20%7Bid%3A%2020%7D%20%7D%2C%20true%20%5D">Try this <strong>R.indexBy</strong> example in Rambda REPL</a>[](#indexBy)
### indexOf
It returns the index of the first element of `list` equals to `valueToFind`.
If there is no such element, it returns `-1`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B0%2C%201%2C%202%2C%203%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.indexOf(2%2C%20list)%2C%0A%20%20R.indexOf(0%2C%20list)%0A%5D%0A%2F%2F%20%3D%3E%20%5B2%2C%20-1%5D">Try this <strong>R.indexOf</strong> example in Rambda REPL</a>[](#indexOf)
### init
```typescript
init<T extends unknown[]>(input: T): T extends readonly [...infer U, any] ? U : [...T]```
It returns all but the last element of list or string `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.init(%5B1%2C%202%2C%203%5D)%20%2C%20%0A%20%20R.init('foo')%20%20%2F%2F%20%3D%3E%20'fo'%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B1%2C%202%5D%2C%20'fo'%5D">Try this <strong>R.init</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptinit<T extends unknown[]>(input: T): T extends readonly [...infer U, any] ? U : [...T];init(input: string): string;```
</details><details><summary><strong>R.init</strong> source</summary>```javascriptimport baseSlice from './_internals/baseSlice.js'
export function init(listOrString){ if (typeof listOrString === 'string') return listOrString.slice(0, -1) return listOrString.length ? baseSlice( listOrString, 0, -1 ) : []}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { init } from './init.js'
test('with array', () => { expect(init([ 1, 2, 3 ])).toEqual([ 1, 2 ]) expect(init([ 1, 2 ])).toEqual([ 1 ]) expect(init([ 1 ])).toEqual([]) expect(init([])).toEqual([]) expect(init([])).toEqual([]) expect(init([ 1 ])).toEqual([])})
test('with string', () => { expect(init('foo')).toBe('fo') expect(init('f')).toBe('') expect(init('')).toBe('')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {init} from 'rambda'
describe('R.init', () => { it('with string', () => { const result = init('foo') result // $ExpectType string }) it('with list - one type', () => { const result = init([1, 2, 3]) result // $ExpectType number[] }) it('with list - mixed types', () => { const result = init([1, 2, 3, 'foo', 'bar']) result // $ExpectType (string | number)[] })})```
</details>[](#init)
### innerJoin
It returns a new list by applying a `predicate` function to all elements of `list1` and `list2` and keeping only these elements where `predicate` returns `true`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list1%20%3D%20%5B1%2C%202%2C%203%2C%204%2C%205%5D%0Aconst%20list2%20%3D%20%5B4%2C%205%2C%206%5D%0Aconst%20predicate%20%3D%20(x%2C%20y)%20%3D%3E%20x%20%3E%3D%20y%0Aconst%20result%20%3D%20R.innerJoin(predicate%2C%20list1%2C%20list2)%0A%2F%2F%20%3D%3E%20%5B4%2C%205%5D">Try this <strong>R.innerJoin</strong> example in Rambda REPL</a>[](#innerJoin)
### insert
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B'a'%2C%20'b'%2C%20'c'%2C%20'd'%2C%20'e'%5D%3B%0Aconst%20result%20%3D%20R.insert(2%2C%20'x'%2C%20list)%3B%0A%2F%2F%20%3D%3E%20%5B'a'%2C%20'b'%2C%20'x'%2C%20'c'%2C%20'd'%2C%20'e'%5D">Try this <strong>R.insert</strong> example in Rambda REPL</a>[](#insert)
### insertAll
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B'a'%2C%20'b'%2C%20'c'%2C%20'd'%2C%20'e'%5D%3B%0Aconst%20result%20%3D%20R.insertAll(2%2C%20%5B'x'%2C%20'y'%2C%20'z'%5D%2C%20list)%3B%0A%2F%2F%20%3D%3E%20%5B'a'%2C%20'b'%2C%20'x'%2C%20'y'%2C%20'z'%2C%20'c'%2C%20'd'%2C%20'e'%5D">Try this <strong>R.insertAll</strong> example in Rambda REPL</a>[](#insertAll)
### intersection
It loops through `listA` and `listB` and returns the intersection of the two according to `R.equals`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20listA%20%3D%20%5B%20%7B%20id%20%3A%201%20%7D%2C%20%7B%20id%20%3A%202%20%7D%2C%20%7B%20id%20%3A%203%20%7D%2C%20%7B%20id%20%3A%204%20%7D%20%5D%0Aconst%20listB%20%3D%20%5B%20%7B%20id%20%3A%203%20%7D%2C%20%7B%20id%20%3A%204%20%7D%2C%20%7B%20id%20%3A%205%20%7D%2C%20%7B%20id%20%3A%206%20%7D%20%5D%0A%0Aconst%20result%20%3D%20R.intersection(listA%2C%20listB)%0A%2F%2F%20%3D%3E%20%5B%7B%20id%20%3A%203%20%7D%2C%20%7B%20id%20%3A%204%20%7D%5D">Try this <strong>R.intersection</strong> example in Rambda REPL</a>[](#intersection)
### intersperse
It adds a `separator` between members of `list`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%200%2C%201%2C%202%2C%203%20%5D%0Aconst%20separator%20%3D%20'%7C'%0Aconst%20result%20%3D%20intersperse(separator%2C%20list)%0A%2F%2F%20%3D%3E%20%5B0%2C%20'%7C'%2C%201%2C%20'%7C'%2C%202%2C%20'%7C'%2C%203%5D">Try this <strong>R.intersperse</strong> example in Rambda REPL</a>[](#intersperse)
### is
It returns `true` if `x` is instance of `targetPrototype`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.is(String%2C%20'foo')%2C%20%20%0A%20%20R.is(Array%2C%201)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.is</strong> example in Rambda REPL</a>[](#is)
### isEmpty
```typescript
isEmpty<T>(x: T): boolean```
It returns `true` if `x` is `empty`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.isEmpty('')%2C%0A%20%20R.isEmpty(%7B%20x%20%3A%200%20%7D)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.isEmpty</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptisEmpty<T>(x: T): boolean;```
</details><details><summary><strong>R.isEmpty</strong> source</summary>```javascriptimport { type } from './type.js'
export function isEmpty(input){ const inputType = type(input) if ([ 'Undefined', 'NaN', 'Number', 'Null' ].includes(inputType)) return false if (!input) return true if (type(input.isEmpty) === 'Function') { return input.isEmpty(); } else if (input.isEmpty) { return !!input.isEmpty; } if (inputType === 'Object'){ return Object.keys(input).length === 0 } if (inputType === 'Array'){ return input.length === 0 } return false}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { isEmpty } from './isEmpty.js'
test('happy', () => { expect(isEmpty(undefined)).toBeFalse() expect(isEmpty('')).toBeTrue() expect(isEmpty(null)).toBeFalse() expect(isEmpty(' ')).toBeFalse() expect(isEmpty(new RegExp(''))).toBeFalse() expect(isEmpty([])).toBeTrue() expect(isEmpty([ [] ])).toBeFalse() expect(isEmpty({})).toBeTrue() expect(isEmpty({ x : 0 })).toBeFalse() expect(isEmpty(0)).toBeFalse() expect(isEmpty(NaN)).toBeFalse() expect(isEmpty([ '' ])).toBeFalse() expect(isEmpty({ isEmpty: false})).toBeFalse() expect(isEmpty({ isEmpty: () => false})).toBeFalse() expect(isEmpty({ isEmpty: true})).toBeTrue() expect(isEmpty({ isEmpty: () => true})).toBeTrue()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {isEmpty} from 'rambda'
describe('R.isEmpty', () => { it('happy', () => { const result = isEmpty('foo') result // $ExpectType boolean })})```
</details>[](#isEmpty)
### isNil
```typescript
isNil(x: any): x is null | undefined```
It returns `true` if `x` is either `null` or `undefined`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.isNil(null)%2C%0A%20%20R.isNil(1)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.isNil</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptisNil(x: any): x is null | undefined;```
</details><details><summary><strong>R.isNil</strong> source</summary>```javascriptexport function isNil(x){ return x === undefined || x === null}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { isNil } from './isNil.js'
test('happy', () => { expect(isNil(null)).toBeTrue() expect(isNil(undefined)).toBeTrue() expect(isNil([])).toBeFalse()})```
</details>[](#isNil)
### isNotNil
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.isNotNil(null)%2C%0A%20%20R.isNotNil(undefined)%2C%0A%20%20R.isNotNil(%5B%5D)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Bfalse%2C%20false%2C%20true%5D">Try this <strong>R.isNotNil</strong> example in Rambda REPL</a>[](#isNotNil)
### join
```typescript
join<T>(glue: string, list: T[]): string```
It returns a string of all `list` instances joined with a `glue`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.join('-'%2C%20%5B1%2C%202%2C%203%5D)%20%20%2F%2F%20%3D%3E%20'1-2-3'">Try this <strong>R.join</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptjoin<T>(glue: string, list: T[]): string;join<T>(glue: string): (list: T[]) => string;```
</details><details><summary><strong>R.join</strong> source</summary>```javascriptexport function join(glue, list){ if (arguments.length === 1) return _list => join(glue, _list) return list.join(glue)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { join } from './join.js'
test('curry', () => { expect(join('|')([ 'foo', 'bar', 'baz' ])).toBe('foo|bar|baz') expect(join('|', [ 1, 2, 3 ])).toBe('1|2|3') const spacer = join(' ') expect(spacer([ 'a', 2, 3.4 ])).toBe('a 2 3.4')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {join} from 'rambda'
describe('R.join', () => { it('happy', () => { const result = join('|', [1, 2, 3]) result // $ExpectType string })})```
</details>[](#join)
### juxt
```typescript
juxt<A extends any[], R1>(fns: [(...a: A) => R1]): (...a: A) => [R1]```
It applies list of function to a list of inputs.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20getRange%20%3D%20juxt(%5B%20Math.min%2C%20Math.max%2C%20Math.min%20%5D)%0Aconst%20result%20%3D%20getRange(%0A%20%203%2C%204%2C%209%2C%20-3%0A)%0A%2F%2F%20%3D%3E%20%5B-3%2C%209%2C%20-3%5D">Try this <strong>R.juxt</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptjuxt<A extends any[], R1>(fns: [(...a: A) => R1]): (...a: A) => [R1];juxt<A extends any[], R1, R2>(fns: [(...a: A) => R1, (...a: A) => R2]): (...a: A) => [R1, R2];juxt<A extends any[], R1, R2, R3>(fns: [(...a: A) => R1, (...a: A) => R2, (...a: A) => R3]): (...a: A) => [R1, R2, R3];juxt<A extends any[], R1, R2, R3, R4>(fns: [(...a: A) => R1, (...a: A) => R2, (...a: A) => R3, (...a: A) => R4]): (...a: A) => [R1, R2, R3, R4];juxt<A extends any[], R1, R2, R3, R4, R5>(fns: [(...a: A) => R1, (...a: A) => R2, (...a: A) => R3, (...a: A) => R4, (...a: A) => R5]): (...a: A) => [R1, R2, R3, R4, R5];juxt<A extends any[], U>(fns: Array<(...args: A) => U>): (...args: A) => U[];```
</details><details><summary><strong>R.juxt</strong> source</summary>```javascriptexport function juxt(listOfFunctions){ return (...args) => listOfFunctions.map(fn => fn(...args))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { juxt } from './juxt.js'
test('happy', () => { const fn = juxt([ Math.min, Math.max, Math.min ]) const result = fn( 3, 4, 9, -3 ) expect(result).toEqual([ -3, 9, -3 ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {juxt} from 'rambda'
describe('R.juxt', () => { it('happy', () => { const fn = juxt([Math.min, Math.max]) const result = fn(3, 4, 9, -3) result // $ExpectType [number, number] })})```
</details>[](#juxt)
### keys
```typescript
keys<T extends object>(x: T): (keyof T & string)[]```
It applies `Object.keys` over `x` and returns its keys.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.keys(%7Ba%3A1%2C%20b%3A2%7D)%20%20%2F%2F%20%3D%3E%20%5B'a'%2C%20'b'%5D">Try this <strong>R.keys</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptkeys<T extends object>(x: T): (keyof T & string)[];keys<T>(x: T): string[];```
</details><details><summary><strong>R.keys</strong> source</summary>```javascriptexport function keys(x){ return Object.keys(x)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { keys } from './keys.js'
test('happy', () => { expect(keys({ a : 1 })).toEqual([ 'a' ])})```
</details>[](#keys)
### last
```typescript
last(str: ''): undefined```
It returns the last element of `input`, as the `input` can be either a string or an array.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.last(%5B1%2C%202%2C%203%5D)%2C%0A%20%20R.last('foo')%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B3%2C%20'o'%5D">Try this <strong>R.last</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptlast(str: ''): undefined;last(str: string): string;last(list: never[]): undefined;last<T extends unknown[]>(array: T): LastArrayElement<T>last<T extends readonly unknown[]>(array: T): LastArrayElement<T>```
</details><details><summary><strong>R.last</strong> source</summary>```javascriptexport function last(listOrString){ if (typeof listOrString === 'string'){ return listOrString[ listOrString.length - 1 ] || '' } return listOrString[ listOrString.length - 1 ]}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { last } from './last.js'
test('with list', () => { expect(last([ 1, 2, 3 ])).toBe(3) expect(last([])).toBeUndefined()})
test('with string', () => { expect(last('abc')).toBe('c') expect(last('')).toBe('')})```
</details>[](#last)
### lastIndexOf
```typescript
lastIndexOf<T>(target: T, list: T[]): number```
It returns the last index of `target` in `list` array.
`R.equals` is used to determine equality between `target` and members of `list`.
If there is no such index, then `-1` is returned.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%201%2C%202%2C%203%5D%0Aconst%20result%20%3D%20%5B%0A%20%20R.lastIndexOf(2%2C%20list)%2C%0A%20%20R.lastIndexOf(4%2C%20list)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B4%2C%20-1%5D">Try this <strong>R.lastIndexOf</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptlastIndexOf<T>(target: T, list: T[]): number;lastIndexOf<T>(target: T): (list: T[]) => number;```
</details><details><summary><strong>R.lastIndexOf</strong> source</summary>```javascriptimport { _lastIndexOf } from './equals.js'
export function lastIndexOf(valueToFind, list){ if (arguments.length === 1){ return _list => _lastIndexOf(valueToFind, _list) } return _lastIndexOf(valueToFind, list)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { lastIndexOf as lastIndexOfRamda } from 'ramda'
import { compareCombinations } from './_internals/testUtils.js'import { possibleIterables, possibleTargets } from './indexOf.spec.js'import { lastIndexOf } from './lastIndexOf.js'
test('with NaN', () => { expect(lastIndexOf(NaN, [ NaN ])).toBe(0)})
test('will throw with bad input', () => { expect(lastIndexOfRamda([], true)).toBe(-1) expect(() => indexOf([], true)).toThrowErrorMatchingInlineSnapshot('"indexOf is not defined"')})
test('without list of objects - no R.equals', () => { expect(lastIndexOf(3, [ 1, 2, 3, 4 ])).toBe(2) expect(lastIndexOf(10)([ 1, 2, 3, 4 ])).toBe(-1)})
test('list of objects uses R.equals', () => { const listOfObjects = [ { a : 1 }, { b : 2 }, { c : 3 } ] expect(lastIndexOf({ c : 4 }, listOfObjects)).toBe(-1) expect(lastIndexOf({ c : 3 }, listOfObjects)).toBe(2)})
test('list of arrays uses R.equals', () => { const listOfLists = [ [ 1 ], [ 2, 3 ], [ 2, 3, 4 ], [ 2, 3 ], [ 1 ], [] ] expect(lastIndexOf([], listOfLists)).toBe(5) expect(lastIndexOf([ 1 ], listOfLists)).toBe(4) expect(lastIndexOf([ 2, 3, 4 ], listOfLists)).toBe(2) expect(lastIndexOf([ 2, 3, 5 ], listOfLists)).toBe(-1)})
test('with string as iterable', () => { expect(() => lastIndexOf('a', 'abc')).toThrowErrorMatchingInlineSnapshot('"Cannot read property \'indexOf\' of abc"') expect(lastIndexOfRamda('a', 'abc')).toBe(0)})
describe('brute force', () => { compareCombinations({ fn : lastIndexOf, fnRamda : lastIndexOfRamda, firstInput : possibleTargets, secondInput : possibleIterables, callback : errorsCounters => { expect(errorsCounters).toMatchInlineSnapshot(` { "ERRORS_MESSAGE_MISMATCH": 0, "ERRORS_TYPE_MISMATCH": 34, "RESULTS_MISMATCH": 0, "SHOULD_NOT_THROW": 51, "SHOULD_THROW": 0, "TOTAL_TESTS": 170, } `) }, })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {lastIndexOf} from 'rambda'
const list = [1, 2, 3]
describe('R.lastIndexOf', () => { it('happy', () => { const result = lastIndexOf(2, list) result // $ExpectType number }) it('curried', () => { const result = lastIndexOf(2)(list) result // $ExpectType number })})```
</details>[](#lastIndexOf)
### length
```typescript
length<T>(input: T[]): number```
It returns the `length` property of list or string `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.length(%5B1%2C%202%2C%203%2C%204%5D)%2C%0A%20%20R.length('foo')%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B4%2C%203%5D">Try this <strong>R.length</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptlength<T>(input: T[]): number;```
</details><details><summary><strong>R.length</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'
export function length(x){ if (isArray(x)) return x.length if (typeof x === 'string') return x.length return NaN}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { length as lengthRamda } from 'ramda'
import { length } from './length.js'
test('happy', () => { expect(length('foo')).toBe(3) expect(length([ 1, 2, 3 ])).toBe(3) expect(length([])).toBe(0)})
test('with empty string', () => { expect(length('')).toBe(0)})
test('with bad input returns NaN', () => { expect(length(0)).toBeNaN() expect(length({})).toBeNaN() expect(length(null)).toBeNaN() expect(length(undefined)).toBeNaN()})
test('with length as property', () => { const input1 = { length : '123' } const input2 = { length : null } const input3 = { length : '' } expect(length(input1)).toBeNaN() expect(lengthRamda(input1)).toBeNaN() expect(length(input2)).toBeNaN() expect(lengthRamda(input2)).toBeNaN() expect(length(input3)).toBeNaN() expect(lengthRamda(input3)).toBeNaN()})```
</details>[](#length)
### lens
```typescript
lens<S, A>(getter: (s: S) => A, setter: (a: A, s: S) => S): Lens<S, A>```
It returns a `lens` for the given `getter` and `setter` functions.
The `getter` **gets** the value of the focus; the `setter` **sets** the value of the focus.
The setter should not mutate the data structure.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20xLens%20%3D%20R.lens(R.prop('x')%2C%20R.assoc('x'))%3B%0A%0AR.view(xLens%2C%20%7Bx%3A%201%2C%20y%3A%202%7D)%20%2F%2F%20%3D%3E%201%0AR.set(xLens%2C%204%2C%20%7Bx%3A%201%2C%20y%3A%202%7D)%20%2F%2F%20%3D%3E%20%7Bx%3A%204%2C%20y%3A%202%7D%0Aconst%20result%20%3D%20R.over(xLens%2C%20R.negate%2C%20%7Bx%3A%201%2C%20y%3A%202%7D)%20%2F%2F%20%3D%3E%20%7Bx%3A%20-1%2C%20y%3A%202%7D">Try this <strong>R.lens</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptlens<S, A>(getter: (s: S) => A, setter: (a: A, s: S) => S): Lens<S, A>;```
</details><details><summary><strong>R.lens</strong> source</summary>```javascriptexport function lens(getter, setter){ return function (functor){ return function (target){ return functor(getter(target)).map(focus => setter(focus, target)) } }}```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {lens, assoc, lensProp, view, lensIndex, lensPath} from 'rambda'
interface Input { foo: string,}const testObject: Input = { foo: 'Jazz',}
describe('R.lens', () => { it('happy', () => { const fn = lens<Input, string>((x: Input) => { x.foo // $ExpectType string return x.foo }, assoc('name')) fn // $ExpectType Lens<Input, string> })})
describe('R.lensProp', () => { it('happy', () => { const result = view<Input, string>(lensProp('foo'), testObject) result // $ExpectType string })})
describe('R.lensIndex', () => { const testList: Input[] = [{foo: 'bar'}, {foo: 'baz'}] it('happy', () => { const result = view<Input[], Input>(lensIndex(0), testList) result // $ExpectType Input result.foo // $ExpectType string })})
describe('R.lensPath', () => { const path = lensPath(['bar', 'a']) it('happy', () => { const result = view<Input, string>(path, testObject) result // $ExpectType string })})
describe('R.view', () => { const fooLens = lens<Input, string>((x: Input) => { return x.foo }, assoc('foo')) it('happt', () => { const result = view<Input, string>(fooLens, testObject) result // $ExpectType string })})```
</details>[](#lens)
### lensIndex
```typescript
lensIndex<A>(n: number): Lens<A[], A>```
It returns a lens that focuses on specified `index`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B'a'%2C%20'b'%2C%20'c'%5D%0Aconst%20headLens%20%3D%20R.lensIndex(0)%0A%0AR.view(headLens%2C%20list)%20%2F%2F%20%3D%3E%20'a'%0AR.set(headLens%2C%20'x'%2C%20list)%20%2F%2F%20%3D%3E%20%5B'x'%2C%20'b'%2C%20'c'%5D%0Aconst%20result%20%3D%20R.over(headLens%2C%20R.toUpper%2C%20list)%20%2F%2F%20%3D%3E%20%5B'A'%2C%20'b'%2C%20'c'%5D">Try this <strong>R.lensIndex</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptlensIndex<A>(n: number): Lens<A[], A>;lensIndex<A extends any[], N extends number>(n: N): Lens<A, A[N]>;```
</details><details><summary><strong>R.lensIndex</strong> source</summary>```javascriptimport { lens } from './lens.js'import { nth } from './nth.js'import { update } from './update.js'
export function lensIndex(index){ return lens(nth(index), update(index))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { compose } from './compose.js'import { keys } from './keys.js'import { lensIndex } from './lensIndex.js'import { over } from './over.js'import { set } from './set.js'import { view } from './view.js'
const testList = [ { a : 1 }, { b : 2 }, { c : 3 } ]
test('focuses list element at the specified index', () => { expect(view(lensIndex(0), testList)).toEqual({ a : 1 })})
test('returns undefined if the specified index does not exist', () => { expect(view(lensIndex(10), testList)).toBeUndefined()})
test('sets the list value at the specified index', () => { expect(set( lensIndex(0), 0, testList )).toEqual([ 0, { b : 2 }, { c : 3 } ])})
test('applies function to the value at the specified list index', () => { expect(over( lensIndex(2), keys, testList )).toEqual([ { a : 1 }, { b : 2 }, [ 'c' ] ])})
test('can be composed', () => { const nestedList = [ 0, [ 10, 11, 12 ], 1, 2 ] const composedLens = compose(lensIndex(1), lensIndex(0)) expect(view(composedLens, nestedList)).toBe(10)})
test('set s (get s) === s', () => { expect(set( lensIndex(0), view(lensIndex(0), testList), testList )).toEqual(testList)})
test('get (set s v) === v', () => { expect(view(lensIndex(0), set( lensIndex(0), 0, testList ))).toBe(0)})
test('get (set(set s v1) v2) === v2', () => { expect(view(lensIndex(0), set( lensIndex(0), 11, set( lensIndex(0), 10, testList ) ))).toBe(11)})```
</details>[](#lensIndex)
### lensPath
It returns a lens that focuses on specified `path`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20lensPath%20%3D%20R.lensPath(%5B'x'%2C%200%2C%20'y'%5D)%0Aconst%20input%20%3D%20%7Bx%3A%20%5B%7By%3A%202%2C%20z%3A%203%7D%2C%20%7By%3A%204%2C%20z%3A%205%7D%5D%7D%0A%0AR.view(lensPath%2C%20input)%20%2F%2F%20%3D%3E%202%0A%0AR.set(lensPath%2C%201%2C%20input)%20%0A%2F%2F%20%3D%3E%20%7Bx%3A%20%5B%7By%3A%201%2C%20z%3A%203%7D%2C%20%7By%3A%204%2C%20z%3A%205%7D%5D%7D%0A%0Aconst%20result%20%3D%20R.over(xHeadYLens%2C%20R.negate%2C%20input)%20%0A%2F%2F%20%3D%3E%20%7Bx%3A%20%5B%7By%3A%20-2%2C%20z%3A%203%7D%2C%20%7By%3A%204%2C%20z%3A%205%7D%5D%7D">Try this <strong>R.lensPath</strong> example in Rambda REPL</a>[](#lensPath)
### lensProp
```typescript
lensProp<S, K extends keyof S = keyof S>(prop: K): Lens<S, S[K]>```
It returns a lens that focuses on specified property `prop`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20xLens%20%3D%20R.lensProp('x')%3B%0Aconst%20input%20%3D%20%7Bx%3A%201%2C%20y%3A%202%7D%0A%0AR.view(xLens%2C%20input)%20%2F%2F%20%3D%3E%201%0A%0AR.set(xLens%2C%204%2C%20input)%20%0A%2F%2F%20%3D%3E%20%7Bx%3A%204%2C%20y%3A%202%7D%0A%0Aconst%20result%20%3D%20R.over(xLens%2C%20R.negate%2C%20input)%20%0A%2F%2F%20%3D%3E%20%7Bx%3A%20-1%2C%20y%3A%202%7D">Try this <strong>R.lensProp</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptlensProp<S, K extends keyof S = keyof S>(prop: K): Lens<S, S[K]>;```
</details><details><summary><strong>R.lensProp</strong> source</summary>```javascriptimport { assoc } from './assoc.js'import { lens } from './lens.js'import { prop } from './prop.js'
export function lensProp(key){ return lens(prop(key), assoc(key))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { compose } from './compose.js'import { identity } from './identity.js'import { inc } from './inc.js'import { lensProp } from './lensProp.js'import { over } from './over.js'import { set } from './set.js'import { view } from './view.js'
const testObj = { a : 1, b : 2, c : 3,}
test('focuses object the specified object property', () => { expect(view(lensProp('a'), testObj)).toBe(1)})
test('returns undefined if the specified property does not exist', () => { expect(view(lensProp('X'), testObj)).toBeUndefined()})
test('sets the value of the object property specified', () => { expect(set( lensProp('a'), 0, testObj )).toEqual({ a : 0, b : 2, c : 3, })})
test('adds the property to the object if it doesn\'t exist', () => { expect(set( lensProp('d'), 4, testObj )).toEqual({ a : 1, b : 2, c : 3, d : 4, })})
test('applies function to the value of the specified object property', () => { expect(over( lensProp('a'), inc, testObj )).toEqual({ a : 2, b : 2, c : 3, })})
test('applies function to undefined and adds the property if it doesn\'t exist', () => { expect(over( lensProp('X'), identity, testObj )).toEqual({ a : 1, b : 2, c : 3, X : undefined, })})
test('can be composed', () => { const nestedObj = { a : { b : 1 }, c : 2, } const composedLens = compose(lensProp('a'), lensProp('b')) expect(view(composedLens, nestedObj)).toBe(1)})
test('set s (get s) === s', () => { expect(set( lensProp('a'), view(lensProp('a'), testObj), testObj )).toEqual(testObj)})
test('get (set s v) === v', () => { expect(view(lensProp('a'), set( lensProp('a'), 0, testObj ))).toBe(0)})
test('get (set(set s v1) v2) === v2', () => { expect(view(lensProp('a'), set( lensProp('a'), 11, set( lensProp('a'), 10, testObj ) ))).toBe(11)})```
</details>[](#lensProp)
### lt
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5BR.lt(2%2C%201)%2C%20R.lt(2%2C%203)%5D%0A%2F%2F%20%3D%3E%20%5Bfalse%2C%20true%5D">Try this <strong>R.lt</strong> example in Rambda REPL</a>[](#lt)
### map
```typescript
map<T, U>(fn: ObjectIterator<T, U>, iterable: Dictionary<T>): Dictionary<U>```
It returns the result of looping through `iterable` with `fn`.
It works with both array and object.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20x%20%3D%3E%20x%20*%202%0Aconst%20fnWhenObject%20%3D%20(val%2C%20prop)%3D%3E%7B%0A%20%20return%20%60%24%7Bprop%7D-%24%7Bval%7D%60%0A%7D%0A%0Aconst%20iterable%20%3D%20%5B1%2C%202%5D%0Aconst%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%7D%0A%0Aconst%20result%20%3D%20%5B%20%0A%20%20R.map(fn%2C%20list)%2C%0A%20%20R.map(fnWhenObject%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5B%20%5B1%2C%204%5D%2C%20%7Ba%3A%20'a-1'%2C%20b%3A%20'b-2'%7D%5D">Try this <strong>R.map</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptmap<T, U>(fn: ObjectIterator<T, U>, iterable: Dictionary<T>): Dictionary<U>;map<T, U>(fn: Iterator<T, U>, iterable: T[]): U[];map<T, U>(fn: Iterator<T, U>): (iterable: T[]) => U[];map<T, U, S>(fn: ObjectIterator<T, U>): (iterable: Dictionary<T>) => Dictionary<U>;map<T>(fn: Iterator<T, T>): (iterable: T[]) => T[];map<T>(fn: Iterator<T, T>, iterable: T[]): T[];```
</details><details><summary><strong>R.map</strong> source</summary>```javascriptimport { INCORRECT_ITERABLE_INPUT } from './_internals/constants.js'import { isArray } from './_internals/isArray.js'import { keys } from './_internals/keys.js'
export function mapArray( fn, list, isIndexed = false){ let index = 0 const willReturn = Array(list.length) while (index < list.length){ willReturn[ index ] = isIndexed ? fn(list[ index ], index) : fn(list[ index ]) index++ } return willReturn}
export function mapObject(fn, obj){ if (arguments.length === 1){ return _obj => mapObject(fn, _obj) } let index = 0 const objKeys = keys(obj) const len = objKeys.length const willReturn = {} while (index < len){ const key = objKeys[ index ] willReturn[ key ] = fn( obj[ key ], key, obj ) index++ } return willReturn}
export const mapObjIndexed = mapObject
export function map(fn, iterable){ if (arguments.length === 1) return _iterable => map(fn, _iterable) if (!iterable){ throw new Error(INCORRECT_ITERABLE_INPUT) } if (isArray(iterable)) return mapArray(fn, iterable) return mapObject(fn, iterable)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { map as mapRamda } from 'ramda'
import { map } from './map.js'
const double = x => x * 2
describe('with array', () => { it('happy', () => { expect(map(double, [ 1, 2, 3 ])).toEqual([ 2, 4, 6 ]) }) it('curried', () => { expect(map(double)([ 1, 2, 3 ])).toEqual([ 2, 4, 6 ]) })})
describe('with object', () => { const obj = { a : 1, b : 2, } it('happy', () => { expect(map(double, obj)).toEqual({ a : 2, b : 4, }) }) it('property as second and input object as third argument', () => { const obj = { a : 1, b : 2, } const iterator = ( val, prop, inputObject ) => { expect(prop).toBeString() expect(inputObject).toEqual(obj) return val * 2 } expect(map(iterator)(obj)).toEqual({ a : 2, b : 4, }) })})
test('bad inputs difference between Ramda and Rambda', () => { expect(() => map(double, null)).toThrowErrorMatchingInlineSnapshot('"Incorrect iterable input"') expect(() => map(double)(undefined)).toThrowErrorMatchingInlineSnapshot('"Incorrect iterable input"') expect(() => mapRamda(double, null)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'fantasy-land/map\')"') expect(() => mapRamda(double, undefined)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of undefined (reading \'fantasy-land/map\')"')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {map} from 'rambda'
describe('R.map with arrays', () => { it('iterable returns the same type as the input', () => { const result = map<number>( (x: number) => { x // $ExpectType number return x + 2 }, [1, 2, 3] ) result // $ExpectType number[] }) it('iterable returns the same type as the input - curried', () => { const result = map<number>((x: number) => { x // $ExpectType number return x + 2 })([1, 2, 3]) result // $ExpectType number[] }) it('iterable returns different type as the input', () => { const result = map<number, string>( (x: number) => { x // $ExpectType number return String(x) }, [1, 2, 3] ) result // $ExpectType string[] })})
describe('R.map with objects', () => { it('iterable with all three arguments - curried', () => { // It requires dummy third typing argument // in order to identify compared to curry typings for arrays // ============================================ const result = map<number, string, any>((a, b, c) => { a // $ExpectType number b // $ExpectType string c // $ExpectType Dictionary<number> return `${a}` })({a: 1, b: 2}) result // $ExpectType Dictionary<string> }) it('iterable with all three arguments', () => { const result = map<number, string>( (a, b, c) => { a // $ExpectType number b // $ExpectType string c // $ExpectType Dictionary<number> return `${a}` }, {a: 1, b: 2} ) result // $ExpectType Dictionary<string> }) it('iterable with property argument', () => { const result = map<number, string>( (a, b) => { a // $ExpectType number b // $ExpectType string return `${a}` }, {a: 1, b: 2} ) result // $ExpectType Dictionary<string> }) it('iterable with no property argument', () => { const result = map<number, string>( a => { a // $ExpectType number return `${a}` }, {a: 1, b: 2} ) result // $ExpectType Dictionary<string> })})```
</details>[](#map)
### mapObjIndexed
```typescript
mapObjIndexed<T>(fn: ObjectIterator<T, T>, iterable: Dictionary<T>): Dictionary<T>```
It works the same way as `R.map` does for objects. It is added as Ramda also has this method.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20(val%2C%20prop)%20%3D%3E%20%7B%0A%20%20return%20%60%24%7Bprop%7D-%24%7Bval%7D%60%0A%7D%0A%0Aconst%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%7D%0A%0Aconst%20result%20%3D%20R.map(mapObjIndexed%2C%20Record%3Cstring%2C%20unknown%3E)%0A%2F%2F%20%3D%3E%20%7Ba%3A%20'a-1'%2C%20b%3A%20'b-2'%7D">Try this <strong>R.mapObjIndexed</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptmapObjIndexed<T>(fn: ObjectIterator<T, T>, iterable: Dictionary<T>): Dictionary<T>;mapObjIndexed<T, U>(fn: ObjectIterator<T, U>, iterable: Dictionary<T>): Dictionary<U>;mapObjIndexed<T>(fn: ObjectIterator<T, T>): (iterable: Dictionary<T>) => Dictionary<T>;mapObjIndexed<T, U>(fn: ObjectIterator<T, U>): (iterable: Dictionary<T>) => Dictionary<U>;```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {mapObjIndexed} from 'rambda'
const obj = {a: 1, b: 2, c: 3}
describe('R.mapObjIndexed', () => { it('without type transform', () => { const result = mapObjIndexed((x, prop, obj) => { x // $ExpectType number prop // $ExpectType string obj // $ExpectType Dictionary<number> return x + 2 }, obj) result // $ExpectType Dictionary<number> }) it('without type transform - curried', () => { const result = mapObjIndexed<number>((x, prop, obj) => { x // $ExpectType number prop // $ExpectType string obj // $ExpectType Dictionary<number> return x + 2 })(obj) result // $ExpectType Dictionary<number> }) it('change of type', () => { const result = mapObjIndexed((x, prop, obj) => { x // $ExpectType number prop // $ExpectType string obj // $ExpectType Dictionary<number> return String(x + 2) }, obj) result // $ExpectType Dictionary<string> }) it('change of type - curried', () => { const result = mapObjIndexed<number, string>((x, prop, obj) => { x // $ExpectType number prop // $ExpectType string obj // $ExpectType Dictionary<number> return String(x + 2) })(obj) result // $ExpectType Dictionary<string> })})```
</details>[](#mapObjIndexed)
### match
```typescript
match(regExpression: RegExp, str: string): string[]```
Curried version of `String.prototype.match` which returns empty array, when there is no match.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.match('a'%2C%20'foo')%2C%0A%20%20R.match(%2F(%5Ba-z%5Da)%2Fg%2C%20'bananas')%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B%5D%2C%20%5B'ba'%2C%20'na'%2C%20'na'%5D%5D">Try this <strong>R.match</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptmatch(regExpression: RegExp, str: string): string[];match(regExpression: RegExp): (str: string) => string[];```
</details><details><summary><strong>R.match</strong> source</summary>```javascriptexport function match(pattern, input){ if (arguments.length === 1) return _input => match(pattern, _input) const willReturn = input.match(pattern) return willReturn === null ? [] : willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { equals } from './equals.js'import { match } from './match.js'
test('happy', () => { expect(match(/a./g)('foo bar baz')).toEqual([ 'ar', 'az' ])})
test('fallback', () => { expect(match(/a./g)('foo')).toEqual([])})
test('with string', () => { expect(match('a', 'foo')).toEqual([]) expect(equals(match('o', 'foo'), [ 'o' ])).toBeTrue()})
test('throwing', () => { expect(() => { match(/a./g, null) }).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'match\')"')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {match} from 'rambda'
const str = 'foo bar'
describe('R.match', () => { it('happy', () => { const result = match(/foo/, str) result // $ExpectType string[] }) it('curried', () => { const result = match(/foo/)(str) result // $ExpectType string[] })})```
</details>[](#match)
### mathMod
`R.mathMod` behaves like the modulo operator should mathematically, unlike the `%` operator (and by extension, `R.modulo`). So while `-17 % 5` is `-2`, `mathMod(-17, 5)` is `3`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.mathMod(-17%2C%205)%2C%0A%20%20R.mathMod(17%2C%205)%2C%0A%20%20R.mathMod(17%2C%20-5)%2C%20%20%0A%20%20R.mathMod(17%2C%200)%20%20%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B3%2C%202%2C%20NaN%2C%20NaN%5D">Try this <strong>R.mathMod</strong> example in Rambda REPL</a>[](#mathMod)
### max
It returns the greater value between `x` and `y`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.max(5%2C%207)%2C%20%20%0A%20%20R.max('bar'%2C%20'foo')%2C%20%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B7%2C%20'foo'%5D">Try this <strong>R.max</strong> example in Rambda REPL</a>[](#max)
### maxBy
It returns the greater value between `x` and `y` according to `compareFn` function.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20compareFn%20%3D%20Math.abs%0A%0Aconst%20result%20%3D%20R.maxBy(compareFn%2C%205%2C%20-7)%20%2F%2F%20%3D%3E%20-7">Try this <strong>R.maxBy</strong> example in Rambda REPL</a>[](#maxBy)
### mean
```typescript
mean(list: number[]): number```
It returns the mean value of `list` input.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.mean(%5B%202%2C%207%20%5D)%0A%2F%2F%20%3D%3E%204.5">Try this <strong>R.mean</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptmean(list: number[]): number;```
</details><details><summary><strong>R.mean</strong> source</summary>```javascriptimport { sum } from './sum.js'
export function mean(list){ return sum(list) / list.length}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { mean } from './mean.js'
test('happy', () => { expect(mean([ 2, 7 ])).toBe(4.5)})
test('with NaN', () => { expect(mean([])).toBeNaN()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {mean} from 'rambda'
describe('R.mean', () => { it('happy', () => { const result = mean([1, 2, 3]) result // $ExpectType number })})```
</details>[](#mean)
### median
```typescript
median(list: number[]): number```
It returns the median value of `list` input.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.median(%5B%207%2C%202%2C%2010%2C%209%20%5D)%20%2F%2F%20%3D%3E%208">Try this <strong>R.median</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptmedian(list: number[]): number;```
</details><details><summary><strong>R.median</strong> source</summary>```javascriptimport { mean } from './mean.js'
export function median(list){ const len = list.length if (len === 0) return NaN const width = 2 - len % 2 const idx = (len - width) / 2 return mean(Array.prototype.slice .call(list, 0) .sort((a, b) => { if (a === b) return 0 return a < b ? -1 : 1 }) .slice(idx, idx + width))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { median } from './median.js'
test('happy', () => { expect(median([ 2 ])).toBe(2) expect(median([ 7, 2, 10, 2, 9 ])).toBe(7)})
test('with empty array', () => { expect(median([])).toBeNaN()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {median} from 'rambda'
describe('R.median', () => { it('happy', () => { const result = median([1, 2, 3]) result // $ExpectType number })})```
</details>[](#median)
### merge
Same as `R.mergeRight`.
[](#merge)
### mergeAll
```typescript
mergeAll<T>(list: object[]): T```
It merges all objects of `list` array sequentially and returns the result.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%0A%20%20%7Ba%3A%201%7D%2C%0A%20%20%7Bb%3A%202%7D%2C%0A%20%20%7Bc%3A%203%7D%0A%5D%0Aconst%20result%20%3D%20R.mergeAll(list)%0Aconst%20expected%20%3D%20%7B%0A%20%20a%3A%201%2C%0A%20%20b%3A%202%2C%0A%20%20c%3A%203%0A%7D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.mergeAll</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptmergeAll<T>(list: object[]): T;mergeAll(list: object[]): object;```
</details><details><summary><strong>R.mergeAll</strong> source</summary>```javascriptimport { map } from './map.js'import { mergeRight } from './mergeRight.js'
export function mergeAll(arr){ let willReturn = {} map(val => { willReturn = mergeRight(willReturn, val) }, arr) return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { mergeAll } from './mergeAll.js'
test('case 1', () => { const arr = [ { a : 1 }, { b : 2 }, { c : 3 } ] const expectedResult = { a : 1, b : 2, c : 3, } expect(mergeAll(arr)).toEqual(expectedResult)})
test('case 2', () => { expect(mergeAll([ { foo : 1 }, { bar : 2 }, { baz : 3 } ])).toEqual({ foo : 1, bar : 2, baz : 3, })})
describe('acts as if nil values are simply empty objects', () => { it('if the first object is nil', () => { expect(mergeAll([ null, { foo : 1 }, { foo : 2 }, { bar : 2 } ])).toEqual({ foo : 2, bar : 2, }) }) it('if the last object is nil', () => { expect(mergeAll([ { foo : 1 }, { foo : 2 }, { bar : 2 }, undefined ])).toEqual({ foo : 2, bar : 2, }) }) it('if an intermediate object is nil', () => { expect(mergeAll([ { foo : 1 }, { foo : 2 }, null, { bar : 2 } ])).toEqual({ foo : 2, bar : 2, }) })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {mergeAll} from 'rambda'
describe('R.mergeAll', () => { it('with passing type', () => { interface Output { foo: number, bar: number, } const result = mergeAll<Output>([{foo: 1}, {bar: 2}]) result.foo // $ExpectType number result.bar // $ExpectType number }) it('without passing type', () => { const result = mergeAll([{foo: 1}, {bar: 2}]) result // $ExpectType unknown })})```
</details>[](#mergeAll)
### mergeDeepLeft
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.mergeDeepLeft(%0A%20%20%7Ba%3A%20%7Bb%3A%201%7D%7D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%202%2C%20c%3A%203%7D%7D%0A)%0A%2F%2F%20%3D%3E%20%7Ba%3A%20%7Bb%3A%201%2C%20c%3A%203%7D%7D">Try this <strong>R.mergeDeepLeft</strong> example in Rambda REPL</a>[](#mergeDeepLeft)
### mergeDeepRight
```typescript
mergeDeepRight<Output>(target: object, newProps: object): Output```
Creates a new object with the own properties of the first object merged with the own properties of the second object. If a key exists in both objects:
- and both values are objects, the two values will be recursively merged - otherwise the value from the second object will be used.<details><summary>All TypeScript definitions</summary>```typescriptmergeDeepRight<Output>(target: object, newProps: object): Output;mergeDeepRight<Output>(target: object): (newProps: object) => Output;```
</details><details><summary><strong>R.mergeDeepRight</strong> source</summary>```javascriptimport { clone } from './clone.js'import { type } from './type.js'
export function mergeDeepRight(target, source){ if (arguments.length === 1){ return sourceHolder => mergeDeepRight(target, sourceHolder) } const willReturn = clone(target) Object.keys(source).forEach(key => { if (type(source[ key ]) === 'Object'){ if (type(target[ key ]) === 'Object'){ willReturn[ key ] = mergeDeepRight(target[ key ], source[ key ]) } else { willReturn[ key ] = source[ key ] } } else { willReturn[ key ] = source[ key ] } }) return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { mergeDeepRight } from './mergeDeepRight.js'
const student = { name : 'foo', age : 10, contact : { a : 1, email : 'foo@example.com', },}const teacher = { age : 40, contact : { email : 'baz@example.com' }, songs : { title : 'Remains the same' },}
test('when merging object with lists inside them', () => { const a = { a : [ 1, 2, 3 ], b : [ 4, 5, 6 ], } const b = { a : [ 7, 8, 9 ], b : [ 10, 11, 12 ], } const result = mergeDeepRight(a, b) const expected = { a : [ 7, 8, 9 ], b : [ 10, 11, 12 ], } expect(result).toEqual(expected)})
test('happy', () => { const result = mergeDeepRight(student, teacher) const curryResult = mergeDeepRight(student)(teacher) const expected = { age : 40, name : 'foo', contact : { a : 1, email : 'baz@example.com', }, songs : { title : 'Remains the same' }, } expect(result).toEqual(expected) expect(curryResult).toEqual(expected)})
test('issue 650', () => { expect(Object.keys(mergeDeepRight({ a : () => {} }, { b : () => {} }))).toEqual([ 'a', 'b', ])})
test('ramda compatible test 1', () => { const a = { w : 1, x : 2, y : { z : 3 }, } const b = { a : 4, b : 5, c : { d : 6 }, } const result = mergeDeepRight(a, b) const expected = { w : 1, x : 2, y : { z : 3 }, a : 4, b : 5, c : { d : 6 }, } expect(result).toEqual(expected)})
test('ramda compatible test 2', () => { const a = { a : { b : 1, c : 2, }, y : 0, } const b = { a : { b : 3, d : 4, }, z : 0, } const result = mergeDeepRight(a, b) const expected = { a : { b : 3, c : 2, d : 4, }, y : 0, z : 0, } expect(result).toEqual(expected)})
test('ramda compatible test 3', () => { const a = { w : 1, x : { y : 2 }, } const result = mergeDeepRight(a, { x : { y : 3 } }) const expected = { w : 1, x : { y : 3 }, } expect(result).toEqual(expected)})
test('functions are not discarded', () => { const obj = { foo : () => {} } expect(typeof mergeDeepRight(obj, {}).foo).toBe('function')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {mergeDeepRight} from 'rambda'
interface Output { foo: { bar: number, },}
describe('R.mergeDeepRight', () => { const result = mergeDeepRight<Output>({foo: {bar: 1}}, {foo: {bar: 2}}) result.foo.bar // $ExpectType number})```
</details>[](#mergeDeepRight)
### mergeLeft
```typescript
mergeLeft<Output>(newProps: object, target: object): Output```
Same as `R.merge`, but in opposite direction.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.mergeLeft(%0A%20%20%7Ba%3A%2010%7D%2C%0A%20%20%7Ba%3A%201%2C%20b%3A%202%7D%0A)%0A%2F%2F%20%3D%3E%20%7Ba%3A10%2C%20b%3A%202%7D">Try this <strong>R.mergeLeft</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptmergeLeft<Output>(newProps: object, target: object): Output;mergeLeft<Output>(newProps: object): (target: object) => Output;```
</details><details><summary><strong>R.mergeLeft</strong> source</summary>```javascriptimport { mergeRight } from './mergeRight.js'
export function mergeLeft(x, y){ if (arguments.length === 1) return _y => mergeLeft(x, _y) return mergeRight(y, x)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { mergeLeft } from './mergeLeft.js'
const obj = { foo : 1, bar : 2,}
test('happy', () => { expect(mergeLeft({ bar : 20 }, obj)).toEqual({ foo : 1, bar : 20, })})
test('curry', () => { expect(mergeLeft({ baz : 3 })(obj)).toEqual({ foo : 1, bar : 2, baz : 3, })})
test('when undefined or null instead of object', () => { expect(mergeLeft(null, undefined)).toEqual({}) expect(mergeLeft(obj, null)).toEqual(obj) expect(mergeLeft(obj, undefined)).toEqual(obj) expect(mergeLeft(undefined, obj)).toEqual(obj)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {mergeLeft} from 'rambda'
interface Output { foo: number, bar: number,}
describe('R.mergeLeft', () => { const result = mergeLeft<Output>({foo: 1}, {bar: 2}) const curriedResult = mergeLeft<Output>({foo: 1})({bar: 2}) result.foo // $ExpectType number result.bar // $ExpectType number curriedResult.bar // $ExpectType number})```
</details>[](#mergeLeft)
### mergeRight
It creates a copy of `target` object with overwritten `newProps` properties. Previously known as `R.merge` but renamed after Ramda did the same.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20target%20%3D%20%7B%20'foo'%3A%200%2C%20'bar'%3A%201%20%7D%0Aconst%20newProps%20%3D%20%7B%20'foo'%3A%207%20%7D%0A%0Aconst%20result%20%3D%20R.mergeRight(target%2C%20newProps)%0A%2F%2F%20%3D%3E%20%7B%20'foo'%3A%207%2C%20'bar'%3A%201%20%7D">Try this <strong>R.mergeRight</strong> example in Rambda REPL</a>[](#mergeRight)
### mergeWith
```typescript
mergeWith(fn: (x: any, z: any) => any, a: Record<string, unknown>, b: Record<string, unknown>): Record<string, unknown>```
It takes two objects and a function, which will be used when there is an overlap between the keys.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.mergeWith(%0A%20%20R.concat%2C%0A%20%20%7Bvalues%20%3A%20%5B%2010%2C%2020%20%5D%7D%2C%0A%20%20%7Bvalues%20%3A%20%5B%2015%2C%2035%20%5D%7D%0A)%0A%2F%2F%20%3D%3E%20%5B%2010%2C%2020%2C%2015%2C%2035%20%5D">Try this <strong>R.mergeWith</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptmergeWith(fn: (x: any, z: any) => any, a: Record<string, unknown>, b: Record<string, unknown>): Record<string, unknown>;mergeWith<Output>(fn: (x: any, z: any) => any, a: Record<string, unknown>, b: Record<string, unknown>): Output;mergeWith(fn: (x: any, z: any) => any, a: Record<string, unknown>): (b: Record<string, unknown>) => Record<string, unknown>;mergeWith<Output>(fn: (x: any, z: any) => any, a: Record<string, unknown>): (b: Record<string, unknown>) => Output;mergeWith(fn: (x: any, z: any) => any): <U, V>(a: U, b: V) => Record<string, unknown>;mergeWith<Output>(fn: (x: any, z: any) => any): <U, V>(a: U, b: V) => Output;```
</details><details><summary><strong>R.mergeWith</strong> source</summary>```javascriptimport { curry } from './curry.js'
export function mergeWithFn( mergeFn, aInput, bInput){ const a = aInput ?? {} const b = bInput ?? {} const willReturn = {} Object.keys(a).forEach(key => { if (b[ key ] === undefined) willReturn[ key ] = a[ key ] else willReturn[ key ] = mergeFn(a[ key ], b[ key ]) }) Object.keys(b).forEach(key => { if (willReturn[ key ] !== undefined) return if (a[ key ] === undefined) willReturn[ key ] = b[ key ] else willReturn[ key ] = mergeFn(a[ key ], b[ key ]) }) return willReturn}
export const mergeWith = curry(mergeWithFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { concat } from './concat.js'import { mergeWithFn } from './mergeWith.js'
test('happy', () => { const result = mergeWithFn( concat, { a : true, values : [ 10, 20 ], }, { b : true, values : [ 15, 35 ], } ) const expected = { a : true, b : true, values : [ 10, 20, 15, 35 ], } expect(result).toEqual(expected)})
// https://github.com/ramda/ramda/pull/3222/files#diff-d925d9188b478d2f1d4b26012c6dddac374f9e9d7a336604d654b9a113bfc857describe('acts as if nil values are simply empty objects', () => { it('if the first object is nil and the second empty', () => { expect(mergeWithFn( concat, undefined, {} )).toEqual({}) }) it('if the first object is empty and the second nil', () => { expect(mergeWithFn( concat, {}, null )).toEqual({}) }) it('if both objects are nil', () => { expect(mergeWithFn( concat, undefined, null )).toEqual({}) }) it('if the first object is not empty and the second is nil', () => { expect(mergeWithFn( concat, { a : 'a' }, null )).toEqual({ a : 'a' }) }) it('if the first object is nil and the second is not empty', () => { expect(mergeWithFn( concat, undefined, { a : 'a' } )).toEqual({ a : 'a' }) })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {concat, mergeWith} from 'rambda'
interface Output { a: boolean, b: boolean, values: number[],}const A = { a: true, values: [10, 20],}const B = { b: true, values: [15, 35],}
describe('R.mergeWith', () => { test('no curry | without explicit types', () => { const result = mergeWith(concat, A, B) result // $ExpectType Record<string, unknown> }) test('no curry | with explicit types', () => { const result = mergeWith<Output>(concat, A, B) result // $ExpectType Output }) test('curry 1 | without explicit types', () => { const result = mergeWith(concat, A)(B) result // $ExpectType Record<string, unknown> }) test('curry 1 | with explicit types', () => { const result = mergeWith<Output>(concat, A)(B) result // $ExpectType Output }) test('curry 2 | without explicit types', () => { const result = mergeWith(concat)(A, B) result // $ExpectType Record<string, unknown> }) test('curry 2 | with explicit types', () => { const result = mergeWith<Output>(concat)(A, B) result // $ExpectType Output })})```
</details>[](#mergeWith)
### min
It returns the lesser value between `x` and `y`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.min(5%2C%207)%2C%20%20%0A%20%20R.min('bar'%2C%20'foo')%2C%20%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B5%2C%20'bar'%5D">Try this <strong>R.min</strong> example in Rambda REPL</a>[](#min)
### minBy
It returns the lesser value between `x` and `y` according to `compareFn` function.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20compareFn%20%3D%20Math.abs%0A%0Aconst%20result%20%3D%20R.minBy(compareFn%2C%20-5%2C%202)%20%2F%2F%20%3D%3E%20-5">Try this <strong>R.minBy</strong> example in Rambda REPL</a>[](#minBy)
### modify
```typescript
modify<T extends object, K extends keyof T, P>( prop: K, fn: (a: T[K]) => P, obj: T,): Omit<T, K> & Record<K, P>```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.modify()%0A%2F%2F%20%3D%3E">Try this <strong>R.modify</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptmodify<T extends object, K extends keyof T, P>( prop: K, fn: (a: T[K]) => P, obj: T,): Omit<T, K> & Record<K, P>;modify<K extends string, A, P>( prop: K, fn: (a: A) => P,): <T extends Record<K, A>>(target: T) => Omit<T, K> & Record<K, P>;```
</details><details><summary><strong>R.modify</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'import { isIterable } from './_internals/isIterable.js'import { curry } from './curry.js'import { updateFn } from './update.js'
function modifyFn( property, fn, iterable){ if (!isIterable(iterable)) return iterable if (iterable[ property ] === undefined) return iterable if (isArray(iterable)){ return updateFn( property, fn(iterable[ property ]), iterable ) } return { ...iterable, [ property ] : fn(iterable[ property ]), }}
export const modify = curry(modifyFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { modify as modifyRamda } from 'ramda'
import { compareCombinations, FALSY_VALUES } from './_internals/testUtils.js'import { add } from './add.js'import { compose } from './compose.js'import { modify } from './modify.js'
const person = { name : 'foo', age : 20,}
test('happy', () => { expect(modify( 'age', x => x + 1, person )).toEqual({ name : 'foo', age : 21, })})
test('property is missing', () => { expect(modify( 'foo', x => x + 1, person )).toEqual(person)})
test('adjust if `array` at the given key with the `transformation` function', () => { expect(modify( 1, add(1), [ 100, 1400 ] )).toEqual([ 100, 1401 ])})
describe('ignores transformations if the input value is not Array and Object', () => { ;[ 42, undefined, null, '' ].forEach(value => { it(`${ value }`, () => { expect(modify( 'a', add(1), value )).toEqual(value) }) })})
const possibleProperties = [ ...FALSY_VALUES, 'foo', 0 ]const possibleTransformers = [ ...FALSY_VALUES, add(1), add('foo'), compose, String,]const possibleObjects = [ ...FALSY_VALUES, {}, [ 1, 2, 3 ], { a : 1, foo : 2, }, { a : 1, foo : [ 1 ], }, { a : 1, foo : 'bar', },]
describe('brute force', () => { compareCombinations({ fn : modify, fnRamda : modifyRamda, firstInput : possibleProperties, secondInput : possibleTransformers, thirdInput : possibleObjects, callback : errorsCounters => { expect(errorsCounters).toMatchInlineSnapshot(` { "ERRORS_MESSAGE_MISMATCH": 0, "ERRORS_TYPE_MISMATCH": 0, "RESULTS_MISMATCH": 0, "SHOULD_NOT_THROW": 0, "SHOULD_THROW": 0, "TOTAL_TESTS": 630, } `) }, })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {modify, add} from 'rambda'const person = {name: 'James', age: 20}
describe('R.modify', () => { it('happy', () => { const {age} = modify('age', add(1), person) const {age: ageAsString} = modify('age', String, person) age // $ExpectType number ageAsString // $ExpectType string }) it('curried', () => { const {age} = modify('age', add(1))(person) age // $ExpectType number })})```
</details>[](#modify)
### modifyPath
It changes a property of object on the base of provided path and transformer function.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.modifyPath('a.b.c'%2C%20x%3D%3E%20x%2B1%2C%20%7Ba%3A%7Bb%3A%20%7Bc%3A1%7D%7D%7D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%7Bb%3A%20%7Bc%3A2%7D%7D%7D">Try this <strong>R.modifyPath</strong> example in Rambda REPL</a>[](#modifyPath)
### modulo
Curried version of `x%y`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.modulo(17%2C%203)%20%2F%2F%20%3D%3E%202">Try this <strong>R.modulo</strong> example in Rambda REPL</a>[](#modulo)
### move
It returns a copy of `list` with exchanged `fromIndex` and `toIndex` elements.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0Aconst%20result%20%3D%20R.move(0%2C%201%2C%20list)%0A%2F%2F%20%3D%3E%20%5B2%2C%201%2C%203%5D">Try this <strong>R.move</strong> example in Rambda REPL</a>[](#move)
### multiply
Curried version of `x*y`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.multiply(2%2C%204)%20%2F%2F%20%3D%3E%208">Try this <strong>R.multiply</strong> example in Rambda REPL</a>[](#multiply)
### negate
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.negate(420)%2F%2F%20%3D%3E%20-420">Try this <strong>R.negate</strong> example in Rambda REPL</a>[](#negate)
### none
```typescript
none<T>(predicate: (x: T) => boolean, list: T[]): boolean```
It returns `true`, if all members of array `list` returns `false`, when applied as argument to `predicate` function.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%200%2C%201%2C%202%2C%203%2C%204%20%5D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3E%206%0A%0Aconst%20result%20%3D%20R.none(predicate%2C%20arr)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.none</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptnone<T>(predicate: (x: T) => boolean, list: T[]): boolean;none<T>(predicate: (x: T) => boolean): (list: T[]) => boolean;```
</details><details><summary><strong>R.none</strong> source</summary>```javascriptexport function none(predicate, list){ if (arguments.length === 1) return _list => none(predicate, _list) for (let i = 0; i < list.length; i++){ if (predicate(list[ i ])) return false } return true}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { none } from './none.js'
const isEven = n => n % 2 === 0
test('when true', () => { expect(none(isEven, [ 1, 3, 5, 7 ])).toBeTrue()})
test('when false curried', () => { expect(none(input => input > 1, [ 1, 2, 3 ])).toBeFalse()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {none} from 'rambda'
describe('R.none', () => { it('happy', () => { const result = none( x => { x // $ExpectType number return x > 0 }, [1, 2, 3] ) result // $ExpectType boolean }) it('curried needs a type', () => { const result = none<number>(x => { x // $ExpectType number return x > 0 })([1, 2, 3]) result // $ExpectType boolean })})```
</details>[](#none)
### not
```typescript
not(input: any): boolean```
It returns a boolean negated version of `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.not(false)%20%2F%2F%20true">Try this <strong>R.not</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptnot(input: any): boolean;```
</details><details><summary><strong>R.not</strong> source</summary>```javascriptexport function not(input){ return !input}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { not } from './not.js'
test('not', () => { expect(not(false)).toBeTrue() expect(not(true)).toBeFalse() expect(not(0)).toBeTrue() expect(not(1)).toBeFalse()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {not} from 'rambda'
describe('R.not', () => { it('happy', () => { const result = not(4) result // $ExpectType boolean })})```
</details>[](#not)
### nth
```typescript
nth(index: number, input: string): string```
Curried version of `input[index]`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0Aconst%20str%20%3D%20'foo'%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.nth(2%2C%20list)%2C%0A%20%20R.nth(6%2C%20list)%2C%0A%20%20R.nth(0%2C%20str)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B3%2C%20undefined%2C%20'f'%5D">Try this <strong>R.nth</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptnth(index: number, input: string): string; nth<T>(index: number, input: T[]): T | undefined; nth(n: number): { <T>(input: T[]): T | undefined; (input: string): string;};```
</details><details><summary><strong>R.nth</strong> source</summary>```javascriptexport function nth(index, input){ if (arguments.length === 1) return _input => nth(index, _input) const idx = index < 0 ? input.length + index : index return Object.prototype.toString.call(input) === '[object String]' ? input.charAt(idx) : input[ idx ]}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { nth } from './nth.js'
test('happy', () => { expect(nth(2, [ 1, 2, 3, 4 ])).toBe(3)})
test('with curry', () => { expect(nth(2)([ 1, 2, 3, 4 ])).toBe(3)})
test('with string and correct index', () => { expect(nth(2)('foo')).toBe('o')})
test('with string and invalid index', () => { expect(nth(20)('foo')).toBe('')})
test('with negative index', () => { expect(nth(-3)([ 1, 2, 3, 4 ])).toBe(2)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {nth} from 'rambda'
const list = [1, 2, 3]
describe('R.nth', () => { it('happy', () => { const result = nth(4, list) result // $ExpectType number | undefined }) it('curried', () => { const result = nth(1)(list) result // $ExpectType number | undefined })})
describe('R.nth - string', () => { const str = 'abc' it('happy', () => { const result = nth(4, str) result // $ExpectType string }) it('curried', () => { const result = nth(1)(str) result // $ExpectType string })})```
</details>[](#nth)
### objOf
It creates an object with a single key-value pair.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.objOf('foo'%2C%20'bar')%0A%2F%2F%20%3D%3E%20%7Bfoo%3A%20'bar'%7D">Try this <strong>R.objOf</strong> example in Rambda REPL</a>[](#objOf)
### of
```typescript
of<T>(x: T): T[]```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.of(null)%3B%20%2F%2F%20%3D%3E%20%5Bnull%5D%0Aconst%20result%20%3D%20R.of(%5B42%5D)%3B%20%2F%2F%20%3D%3E%20%5B%5B42%5D%5D">Try this <strong>R.of</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptof<T>(x: T): T[];```
</details><details><summary><strong>R.of</strong> source</summary>```javascriptexport function of(value){ return [ value ]}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { of } from './of.js'
test('happy', () => { expect(of(3)).toEqual([ 3 ]) expect(of(null)).toEqual([ null ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {of} from 'rambda'
const list = [1, 2, 3]
describe('R.of', () => { it('happy', () => { const result = of(4) result // $ExpectType number[] }) it('curried', () => { const result = of(list) result // $ExpectType number[][] })})```
</details>[](#of)
### omit
```typescript
omit<T, K extends string>(propsToOmit: K[], obj: T): Omit<T, K>```
It returns a partial copy of an `obj` without `propsToOmit` properties.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D%0Aconst%20propsToOmit%20%3D%20'a%2Cc%2Cd'%0Aconst%20propsToOmitList%20%3D%20%5B'a'%2C%20'c'%2C%20'd'%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.omit(propsToOmit%2C%20Record%3Cstring%2C%20unknown%3E)%2C%20%0A%20%20R.omit(propsToOmitList%2C%20Record%3Cstring%2C%20unknown%3E)%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B%7Bb%3A%202%7D%2C%20%7Bb%3A%202%7D%5D">Try this <strong>R.omit</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptomit<T, K extends string>(propsToOmit: K[], obj: T): Omit<T, K>;omit<K extends string>(propsToOmit: K[]): <T>(obj: T) => Omit<T, K>;omit<T, U>(propsToOmit: string, obj: T): U;omit<T, U>(propsToOmit: string): (obj: T) => U;omit<T>(propsToOmit: string, obj: object): T;omit<T>(propsToOmit: string): (obj: object) => T;```
</details><details><summary><strong>R.omit</strong> source</summary>```javascriptimport { createPath } from './_internals/createPath.js'import { includes } from './_internals/includes.js'
export function omit(propsToOmit, obj){ if (arguments.length === 1) return _obj => omit(propsToOmit, _obj) if (obj === null || obj === undefined) return undefined const propsToOmitValue = createPath(propsToOmit, ',') const willReturn = {} for (const key in obj) if (!includes(key, propsToOmitValue)) willReturn[ key ] = obj[ key ] return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { omit } from './omit.js'
test('with string as condition', () => { const obj = { a : 1, b : 2, c : 3, } const result = omit('a,c', obj) const resultCurry = omit('a,c')(obj) const expectedResult = { b : 2 } expect(result).toEqual(expectedResult) expect(resultCurry).toEqual(expectedResult)})
test.only('with number as property to omit', () => { const obj = { 1 : 1, b : 2, } const result = omit([ 1 ], obj) expect(result).toEqual({ b : 2 })})
test('with null', () => { expect(omit('a,b', null)).toBeUndefined()})
test('happy', () => { expect(omit([ 'a', 'c' ])({ a : 'foo', b : 'bar', c : 'baz', })).toEqual({ b : 'bar' })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {omit} from 'rambda'
describe('R.omit with array as props input', () => { it('allow Typescript to infer object type', () => { const input = {a: 'foo', b: 2, c: 3, d: 4} const result = omit(['b,c'], input) result.a // $ExpectType string result.d // $ExpectType number const curriedResult = omit(['a,c'], input) curriedResult.a // $ExpectType string curriedResult.d // $ExpectType number }) it('declare type of input object', () => { interface Input { a: string, b: number, c: number, d: number, } const input: Input = {a: 'foo', b: 2, c: 3, d: 4} const result = omit(['b,c'], input) result // $ExpectType Omit<Input, "b,c"> result.a // $ExpectType string result.d // $ExpectType number const curriedResult = omit(['a,c'], input) curriedResult.a // $ExpectType string curriedResult.d // $ExpectType number })})
describe('R.omit with string as props input', () => { interface Output { b: number, d: number, } it('explicitly declare output', () => { const result = omit<Output>('a,c', {a: 1, b: 2, c: 3, d: 4}) result // $ExpectType Output result.b // $ExpectType number const curriedResult = omit<Output>('a,c')({a: 1, b: 2, c: 3, d: 4}) curriedResult.b // $ExpectType number }) it('explicitly declare input and output', () => { interface Input { a: number, b: number, c: number, d: number, } const result = omit<Input, Output>('a,c', {a: 1, b: 2, c: 3, d: 4}) result // $ExpectType Output result.b // $ExpectType number const curriedResult = omit<Input, Output>('a,c')({ a: 1, b: 2, c: 3, d: 4, }) curriedResult.b // $ExpectType number }) it('without passing type', () => { const result = omit('a,c', {a: 1, b: 2, c: 3, d: 4}) result // $ExpectType unknown })})```
</details>[](#omit)
### on
It passes the two inputs through `unaryFn` and then the results are passed as inputs the the `binaryFn` to receive the final result(`binaryFn(unaryFn(FIRST_INPUT), unaryFn(SECOND_INPUT))`).
This method is also known as P combinator.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.on((a%2C%20b)%20%3D%3E%20a%20%2B%20b%2C%20R.prop('a')%2C%20%7Bb%3A0%2C%20a%3A1%7D%2C%20%7Ba%3A2%7D)%0A%2F%2F%20%3D%3E%203">Try this <strong>R.on</strong> example in Rambda REPL</a>[](#on)
### once
```typescript
once<T extends AnyFunction>(func: T): T```
It returns a function, which invokes only once `fn` function.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?let%20result%20%3D%200%0Aconst%20addOnce%20%3D%20R.once((x)%20%3D%3E%20result%20%3D%20result%20%2B%20x)%0A%0AaddOnce(1)%0Aconst%20result%20%3D%20addOnce(1)%0A%2F%2F%20%3D%3E%201">Try this <strong>R.once</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptonce<T extends AnyFunction>(func: T): T;```
</details><details><summary><strong>R.once</strong> source</summary>```javascriptimport { curry } from './curry.js'
function onceFn(fn, context){ let result return function (){ if (fn){ result = fn.apply(context || this, arguments) fn = null } return result }}
export function once(fn, context){ if (arguments.length === 1){ const wrap = onceFn(fn, context) return curry(wrap) } return onceFn(fn, context)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { once } from './once.js'
test('with counter', () => { let counter = 0 const runOnce = once(x => { counter++ return x + 2 }) expect(runOnce(1)).toBe(3) runOnce(1) runOnce(1) runOnce(1) expect(counter).toBe(1)})
test('happy path', () => { const addOneOnce = once(( a, b, c ) => a + b + c, 1) expect(addOneOnce( 10, 20, 30 )).toBe(60) expect(addOneOnce(40)).toBe(60)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {once} from 'rambda'
describe('R.once', () => { it('happy', () => { const runOnce = once((x: number) => { return x + 2 }) const result = runOnce(1) result // $ExpectType number })})```
</details>[](#once)
### or
Logical OR
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?R.or(false%2C%20true)%3B%20%2F%2F%20%3D%3E%20true%0AR.or(false%2C%20false)%3B%20%2F%2F%20%3D%3E%20false%0Aconst%20result%20%3D%20R.or(false%2C%20'foo')%3B%20%2F%2F%20%3D%3E%20'foo'">Try this <strong>R.or</strong> example in Rambda REPL</a>[](#or)
### over
```typescript
over<S, A>(lens: Lens<S, A>): { (fn: (a: A) => A): (value: S) => S```
It returns a copied **Object** or **Array** with modified value received by applying function `fn` to `lens` focus.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20headLens%20%3D%20R.lensIndex(0)%0A%20%0Aconst%20result%20%3D%20R.over(headLens%2C%20R.toUpper%2C%20%5B'foo'%2C%20'bar'%2C%20'baz'%5D)%20%2F%2F%20%3D%3E%20%5B'FOO'%2C%20'bar'%2C%20'baz'%5D">Try this <strong>R.over</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptover<S, A>(lens: Lens<S, A>): { (fn: (a: A) => A): (value: S) => S; (fn: (a: A) => A, value: S): S;};over<S, A>(lens: Lens<S, A>, fn: (a: A) => A): (value: S) => S;over<S, A>(lens: Lens<S, A>, fn: (a: A) => A, value: S): S;```
</details><details><summary><strong>R.over</strong> source</summary>```javascriptimport { curry } from './curry.js'
const Identity = x => ({ x, map : fn => Identity(fn(x)),})
function overFn( lens, fn, object){ return lens(x => Identity(fn(x)))(object).x}
export const over = curry(overFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { assoc } from './assoc.js'import { lens } from './lens.js'import { lensIndex } from './lensIndex.js'import { lensPath } from './lensPath.js'import { over } from './over.js'import { prop } from './prop.js'import { toUpper } from './toUpper.js'
const testObject = { foo : 'bar', baz : { a : 'x', b : 'y', },}
test('assoc lens', () => { const assocLens = lens(prop('foo'), assoc('foo')) const result = over( assocLens, toUpper, testObject ) const expected = { ...testObject, foo : 'BAR', } expect(result).toEqual(expected)})
test('path lens', () => { const pathLens = lensPath('baz.a') const result = over( pathLens, toUpper, testObject ) const expected = { ...testObject, baz : { a : 'X', b : 'y', }, } expect(result).toEqual(expected)})
test('index lens', () => { const indexLens = lensIndex(0) const result = over(indexLens, toUpper)([ 'foo', 'bar' ]) expect(result).toEqual([ 'FOO', 'bar' ])})```
</details>[](#over)
### partial
```typescript
partial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T```
It is very similar to `R.curry`, but you can pass initial arguments when you create the curried function.
`R.partial` will keep returning a function until all the arguments that the function `fn` expects are passed.The name comes from the fact that you partially inject the inputs.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20(title%2C%20firstName%2C%20lastName)%20%3D%3E%20%7B%0A%20%20return%20title%20%2B%20'%20'%20%2B%20firstName%20%2B%20'%20'%20%2B%20lastName%20%2B%20'!'%0A%7D%0A%0Aconst%20canPassAnyNumberOfArguments%20%3D%20R.partial(fn%2C%20'Hello')%0Aconst%20ramdaStyle%20%3D%20R.partial(fn%2C%20%5B'Hello'%5D)%0A%0Aconst%20finalFn%20%3D%20canPassAnyNumberOfArguments('Foo')%0A%0Aconst%20result%20%3D%20finalFn('Bar')%20%2F%2F%20%3D%3E%20%20'Hello%2C%20Foo%20Bar!'">Try this <strong>R.partial</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpartial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T;partial<V0, V1, V2, T>(fn: (x0: V0, x1: V1, x2: V2) => T, args: [V0, V1]): (x2: V2) => T;partial<V0, V1, V2, T>(fn: (x0: V0, x1: V1, x2: V2) => T, args: [V0]): (x1: V1, x2: V2) => T;partial<V0, V1, V2, V3, T>( fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, args: [V0, V1, V2],): (x2: V3) => T;partial<V0, V1, V2, V3, T>( fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, args: [V0, V1],): (x2: V2, x3: V3) => T;partial<V0, V1, V2, V3, T>( fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, args: [V0],): (x1: V1, x2: V2, x3: V3) => T;partial<T>(fn: (...a: any[]) => T, args: any[]): (...a: any[]) => T;```
</details><details><summary><strong>R.partial</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'
export function partial(fn, ...args){ const len = fn.length // If a single array argument is given, those are the args (a la Ramda). // Otherwise, the variadic arguments are the args. const argList = args.length === 1 && isArray(args[0]) ? args[0] : args return (...rest) => { if (argList.length + rest.length >= len){ return fn(...argList, ...rest) } return partial(fn, ...[ ...argList, ...rest ]) }}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { partial } from './partial.js'import { type } from './type.js'
const greet = ( salutation, title, firstName, lastName) => [salutation, title, firstName, lastName]test('happy', () => { const canPassAnyNumberOfArguments = partial( greet, 'Hello', 'Ms.' ) const fn = canPassAnyNumberOfArguments('foo') const sayHello = partial(greet, [ 'Hello' ]) const sayHelloRamda = partial(sayHello, [ 'Ms.' ]) expect(type(fn)).toBe('Function') expect(fn('bar')).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar']) expect(sayHelloRamda('foo', 'bar')).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar'])})
test('extra arguments are ignored', () => { const canPassAnyNumberOfArguments = partial( greet, 'Hello', 'Ms.' ) const fn = canPassAnyNumberOfArguments('foo') expect(type(fn)).toBe('Function') expect(fn( 'bar', 1, 2 )).toStrictEqual(['Hello', 'Ms.', 'foo', 'bar'])})
test('when array is input', () => { const fooFn = ( a, b, c, d ) => ({ a, b, c, d, }) const barFn = partial( fooFn, [ 1, 2 ], [] ) expect(barFn(1, 2)).toEqual({ a : [ 1, 2 ], b : [], c : 1, d : 2, })})
test('ramda spec', () => { const sayHello = partial(greet, 'Hello') const sayHelloToMs = partial(sayHello, 'Ms.') expect(sayHelloToMs('Jane', 'Jones')).toStrictEqual(['Hello', 'Ms.', 'Jane', 'Jones'])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {partial} from 'rambda'
describe('R.partial', () => { it('happy', () => { function fn( aString: string, aNumber: number, aBoolean: boolean, aNull: null ) { return {aString, aNumber, aBoolean, aNull} } // @ts-expect-error partial(fn, 1) const fn1 = partial(fn, ['a']) partial(fn1, ['b']) const fn2 = partial(fn1, [2]) const result = fn2(true, null) result // $ExpectType { aString: string; aNumber: number; aBoolean: boolean; aNull: null; } })})```
</details>[](#partial)
### partialObject
```typescript
partialObject<Input, PartialInput, Output>( fn: (input: Input) => Output, partialInput: PartialInput,): (input: Pick<Input, Exclude<keyof Input, keyof PartialInput>>) => Output```
`R.partialObject` is a curry helper designed specifically for functions accepting object as a single argument.
Initially the function knows only a part from the whole input object and then `R.partialObject` helps in preparing the function for the second part, when it receives the rest of the input.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20(%7B%20a%2C%20b%2C%20c%20%7D)%20%3D%3E%20a%20%2B%20b%20%2B%20c%0Aconst%20curried%20%3D%20R.partialObject(fn%2C%20%7B%20a%20%3A%201%20%7D)%0Aconst%20result%20%3D%20curried(%7B%0A%20%20b%20%3A%202%2C%0A%20%20c%20%3A%203%2C%0A%7D)%0A%2F%2F%20%3D%3E%206">Try this <strong>R.partialObject</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpartialObject<Input, PartialInput, Output>( fn: (input: Input) => Output, partialInput: PartialInput,): (input: Pick<Input, Exclude<keyof Input, keyof PartialInput>>) => Output;```
</details><details><summary><strong>R.partialObject</strong> source</summary>```javascriptimport { mergeDeepRight } from './mergeDeepRight.js'
export function partialObject(fn, input){ return nextInput => fn(mergeDeepRight(nextInput, input))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { delay } from './delay.js'import { partialObject } from './partialObject.js'import { type } from './type.js'
test('with plain function', () => { const fn = ({ a, b, c }) => a + b + c const curried = partialObject(fn, { a : 1 }) expect(type(curried)).toBe('Function') expect(curried({ b : 2, c : 3, })).toBe(6)})
test('with function that throws an error', () => { const fn = ({ a, b, c }) => { throw new Error('foo') } const curried = partialObject(fn, { a : 1 }) expect(type(curried)).toBe('Function') expect(() => curried({ b : 2, c : 3, })).toThrowErrorMatchingInlineSnapshot('"foo"')})
test('with async', async () => { const fn = async ({ a, b, c }) => { await delay(100) return a + b + c } const curried = partialObject(fn, { a : 1 }) const result = await curried({ b : 2, c : 3, }) expect(result).toBe(6)})
test('async function throwing an error', async () => { const fn = async ({ a, b, c }) => { await delay(100) throw new Error('foo') } const curried = partialObject(fn, { a : 1 }) try { await curried({ b : 2, c : 3, }) expect(true).toBeFalsy() } catch (e){ expect(e.message).toBe('foo') }})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {partialObject, delay} from 'rambda'
describe('R.partialObject', () => { it('happy', () => { interface Input { a: number, b: number, c: string, } const fn = ({a, b, c}: Input) => a + b + c const curried = partialObject(fn, {a: 1}) const result = curried({ b: 2, c: 'foo', }) result // $ExpectType string }) it('asynchronous', async() => { interface Input { a: number, b: number, c: string, } const fn = async({a, b, c}: Input) => { await delay(100) return a + b + c } const curried = partialObject(fn, {a: 1}) const result = await curried({ b: 2, c: 'foo', }) result // $ExpectType string })})```
</details>[](#partialObject)
### partition
```typescript
partition<T>( predicate: Predicate<T>, input: T[]): [T[], T[]]```
It will return array of two objects/arrays according to `predicate` function. The first member holds all instances of `input` that pass the `predicate` function, while the second member - those who doesn't.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0Aconst%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3E%202%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.partition(predicate%2C%20list)%2C%0A%20%20R.partition(predicate%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0Aconst%20expected%20%3D%20%5B%0A%20%20%5B%5B3%5D%2C%20%5B1%2C%202%5D%5D%2C%0A%20%20%5B%7Bc%3A%203%7D%2C%20%20%7Ba%3A%201%2C%20b%3A%202%7D%5D%2C%0A%5D%0A%2F%2F%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.partition</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpartition<T>( predicate: Predicate<T>, input: T[]): [T[], T[]];partition<T>( predicate: Predicate<T>): (input: T[]) => [T[], T[]];partition<T>( predicate: (x: T, prop?: string) => boolean, input: { [key: string]: T}): [{ [key: string]: T}, { [key: string]: T}];partition<T>( predicate: (x: T, prop?: string) => boolean): (input: { [key: string]: T}) => [{ [key: string]: T}, { [key: string]: T}];```
</details><details><summary><strong>R.partition</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'
export function partitionObject(predicate, iterable){ const yes = {} const no = {} Object.entries(iterable).forEach(([ prop, value ]) => { if (predicate(value, prop)){ yes[ prop ] = value } else { no[ prop ] = value } }) return [ yes, no ]}
export function partitionArray( predicate, list, indexed = false){ const yes = [] const no = [] let counter = -1 while (counter++ < list.length - 1){ if ( indexed ? predicate(list[ counter ], counter) : predicate(list[ counter ]) ){ yes.push(list[ counter ]) } else { no.push(list[ counter ]) } } return [ yes, no ]}
export function partition(predicate, iterable){ if (arguments.length === 1){ return listHolder => partition(predicate, listHolder) } if (!isArray(iterable)) return partitionObject(predicate, iterable) return partitionArray(predicate, iterable)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { partition } from './partition.js'
test('with array', () => { const predicate = x => x > 2 const list = [ 1, 2, 3, 4 ] const result = partition(predicate, list) const expectedResult = [ [ 3, 4 ], [ 1, 2 ], ] expect(result).toEqual(expectedResult)})
test('with object', () => { const predicate = (value, prop) => { expect(typeof prop).toBe('string') return value > 2 } const hash = { a : 1, b : 2, c : 3, d : 4, } const result = partition(predicate)(hash) const expectedResult = [ { c : 3, d : 4, }, { a : 1, b : 2, }, ] expect(result).toEqual(expectedResult)})
test('readme example', () => { const list = [ 1, 2, 3 ] const obj = { a : 1, b : 2, c : 3, } const predicate = x => x > 2 const result = [ partition(predicate, list), partition(predicate, obj) ] const expected = [ [ [ 3 ], [ 1, 2 ] ], [ { c : 3 }, { a : 1, b : 2, }, ], ] expect(result).toEqual(expected)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {partition} from 'rambda'
describe('R.partition', () => { it('with array', () => { const predicate = (x: number) => { return x > 2 } const list = [1, 2, 3, 4] const result = partition(predicate, list) const curriedResult = partition(predicate)(list) result // $ExpectType [number[], number[]] curriedResult // $ExpectType [number[], number[]] }) /* revert to old version of `dtslint` and `R.partition` typing as there is diff between VSCode types(correct) and dtslint(incorrect) it('with object', () => { const predicate = (value: number, prop?: string) => { return value > 2 } const hash = { a: 1, b: 2, c: 3, d: 4, } const result = partition(predicate, hash) const curriedResult = partition(predicate)(hash) result[0] // $xExpectType { [key: string]: number; } result[1] // $xExpectType { [key: string]: number; } curriedResult[0] // $xExpectType { [key: string]: number; } curriedResult[1] // $xExpectType { [key: string]: number; } }) */})```
</details>[](#partition)
### path
```typescript
path<S, K0 extends keyof S = keyof S>(path: [K0], obj: S): S[K0]```
If `pathToSearch` is `'a.b'` then it will return `1` if `obj` is `{a:{b:1}}`.
It will return `undefined`, if such path is not found.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%20%7Bb%3A%201%7D%7D%0Aconst%20pathToSearch%20%3D%20'a.b'%0Aconst%20pathToSearchList%20%3D%20%5B'a'%2C%20'b'%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.path(pathToSearch%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.path(pathToSearchList%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.path('a.b.c.d'%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5B1%2C%201%2C%20undefined%5D">Try this <strong>R.path</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpath<S, K0 extends keyof S = keyof S>(path: [K0], obj: S): S[K0];path<S, K0 extends keyof S = keyof S, K1 extends keyof S[K0] = keyof S[K0]>(path: [K0, K1], obj: S): S[K0][K1];path< S, K0 extends keyof S = keyof S, K1 extends keyof S[K0] = keyof S[K0], K2 extends keyof S[K0][K1] = keyof S[K0][K1]>(path: [K0, K1, K2], obj: S): S[K0][K1][K2];path< S, K0 extends keyof S = keyof S, K1 extends keyof S[K0] = keyof S[K0], K2 extends keyof S[K0][K1] = keyof S[K0][K1], K3 extends keyof S[K0][K1][K2] = keyof S[K0][K1][K2],>(path: [K0, K1, K2, K3], obj: S): S[K0][K1][K2][K3];path< S, K0 extends keyof S = keyof S, K1 extends keyof S[K0] = keyof S[K0], K2 extends keyof S[K0][K1] = keyof S[K0][K1], K3 extends keyof S[K0][K1][K2] = keyof S[K0][K1][K2], K4 extends keyof S[K0][K1][K2][K3] = keyof S[K0][K1][K2][K3],>(path: [K0, K1, K2, K3, K4], obj: S): S[K0][K1][K2][K3][K4];path< S, K0 extends keyof S = keyof S, K1 extends keyof S[K0] = keyof S[K0], K2 extends keyof S[K0][K1] = keyof S[K0][K1], K3 extends keyof S[K0][K1][K2] = keyof S[K0][K1][K2], K4 extends keyof S[K0][K1][K2][K3] = keyof S[K0][K1][K2][K3], K5 extends keyof S[K0][K1][K2][K3][K4] = keyof S[K0][K1][K2][K3][K4],>(path: [K0, K1, K2, K3, K4, K5], obj: S): S[K0][K1][K2][K3][K4][K5];path<T>(pathToSearch: string, obj: any): T | undefined;path<T>(pathToSearch: string): (obj: any) => T | undefined;path<T>(pathToSearch: RamdaPath): (obj: any) => T | undefined;path<T>(pathToSearch: RamdaPath, obj: any): T | undefined;```
</details><details><summary><strong>R.path</strong> source</summary>```javascriptimport { createPath } from './_internals/createPath.js'
export function pathFn(pathInput, obj){ let willReturn = obj let counter = 0 const pathArrValue = createPath(pathInput) while (counter < pathArrValue.length){ if (willReturn === null || willReturn === undefined){ return undefined } if (willReturn[ pathArrValue[ counter ] ] === null) return undefined willReturn = willReturn[ pathArrValue[ counter ] ] counter++ } return willReturn}
export function path(pathInput, obj){ if (arguments.length === 1) return _obj => path(pathInput, _obj) if (obj === null || obj === undefined){ return undefined } return pathFn(pathInput, obj)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { path } from './path.js'
test('with array inside object', () => { const obj = { a : { b : [ 1, { c : 1 } ] } } expect(path('a.b.1.c', obj)).toBe(1)})
test('works with undefined', () => { const obj = { a : { b : { c : 1 } } } expect(path('a.b.c.d.f', obj)).toBeUndefined() expect(path('foo.babaz', undefined)).toBeUndefined() expect(path('foo.babaz')(undefined)).toBeUndefined()})
test('works with string instead of array', () => { expect(path('foo.bar.baz')({ foo : { bar : { baz : 'yes' } } })).toBe('yes')})
test('path', () => { expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : { baz : 'yes' } } })).toBe('yes') expect(path([ 'foo', 'bar', 'baz' ])(null)).toBeUndefined() expect(path([ 'foo', 'bar', 'baz' ])({ foo : { bar : 'baz' } })).toBeUndefined()})
test('null is not a valid path', () => { expect(path('audio_tracks', { a : 1, audio_tracks : null, })).toBeUndefined()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {path} from 'rambda'
const input = {a: {b: {c: true}}}
describe('R.path with string as path', () => { it('without specified output type', () => { // $ExpectType unknown path('a.b.c', input) // $ExpectType unknown path('a.b.c')(input) }) it('with specified output type', () => { // $ExpectType boolean | undefined path<boolean>('a.b.c', input) // $ExpectType boolean | undefined path<boolean>('a.b.c')(input) })})
describe('R.path with list as path', () => { it('with array as path', () => { // $ExpectType boolean path(['a', 'b', 'c'], input) // $ExpectType unknown path(['a', 'b', 'c'])(input) }) test('shallow property', () => { // $ExpectType number path(['a'], {a: 1}) // $ExpectType unknown path(['b'], {a: 1}) }) test('deep property', () => { const testObject = {a: {b: {c: {d: {e: {f: 1}}}}}} const result = path(['a', 'b', 'c', 'd', 'e', 'f'], testObject) // $ExpectType number result const curriedResult = path(['a', 'b', 'c', 'd', 'e', 'f'])(testObject) // $ExpectType unknown curriedResult }) test('issue #668 - path is not correct', () => { const object = { is: { a: 'path', }, } const result = path(['is', 'not', 'a'], object) // $ExpectType unknown result const curriedResult = path(['is', 'not', 'a'])(object) // $ExpectType unknown curriedResult })})```
</details>[](#path)
### pathEq
```typescript
pathEq(pathToSearch: Path, target: any, input: any): boolean```
It returns `true` if `pathToSearch` of `input` object is equal to `target` value.
`pathToSearch` is passed to `R.path`, which means that it can be either a string or an array. Also equality between `target` and the found value is determined by `R.equals`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20path%20%3D%20'a.b'%0Aconst%20target%20%3D%20%7Bc%3A%201%7D%0Aconst%20input%20%3D%20%7Ba%3A%20%7Bb%3A%20%7Bc%3A%201%7D%7D%7D%0A%0Aconst%20result%20%3D%20R.pathEq(%0A%20%20path%2C%0A%20%20target%2C%0A%20%20input%0A)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.pathEq</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpathEq(pathToSearch: Path, target: any, input: any): boolean;pathEq(pathToSearch: Path, target: any): (input: any) => boolean;pathEq(pathToSearch: Path): (target: any) => (input: any) => boolean;```
</details><details><summary><strong>R.pathEq</strong> source</summary>```javascriptimport { curry } from './curry.js'import { equals } from './equals.js'import { path } from './path.js'
function pathEqFn( pathToSearch, target, input){ return equals(path(pathToSearch, input), target)}
export const pathEq = curry(pathEqFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { pathEq } from './pathEq.js'
test('when true', () => { const path = 'a.b' const obj = { a : { b : { c : 1 } } } const target = { c : 1 } expect(pathEq( path, target, obj )).toBeTrue()})
test('when false', () => { const path = 'a.b' const obj = { a : { b : 1 } } const target = 2 expect(pathEq(path, target)(obj)).toBeFalse()})
test('when wrong path', () => { const path = 'foo.bar' const obj = { a : { b : 1 } } const target = 2 expect(pathEq( path, target, obj )).toBeFalse()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {pathEq} from 'rambda'
describe('R.pathEq', () => { it('with string path', () => { const pathToSearch = 'a.b.c' const input = {a: {b: {c: 1}}} const target = {c: 1} const result = pathEq(pathToSearch, input, target) const curriedResult = pathEq(pathToSearch, input, target) result // $ExpectType boolean curriedResult // $ExpectType boolean }) it('with array path', () => { const pathToSearch = ['a', 'b', 'c'] const input = {a: {b: {c: 1}}} const target = {c: 1} const result = pathEq(pathToSearch, input, target) const curriedResult = pathEq(pathToSearch, input, target) result // $ExpectType boolean curriedResult // $ExpectType boolean })})
describe('with ramda specs', () => { const testPath = ['x', 0, 'y'] const testObj = { x: [ {y: 2, z: 3}, {y: 4, z: 5}, ], } const result1 = pathEq(testPath, 2, testObj) const result2 = pathEq(testPath, 2)(testObj) const result3 = pathEq(testPath)(2)(testObj) result1 // $ExpectType boolean result2 // $ExpectType boolean result3 // $ExpectType boolean})```
</details>[](#pathEq)
### pathOr
```typescript
pathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T```
It reads `obj` input and returns either `R.path(pathToSearch, Record<string, unknown>)` result or `defaultValue` input.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20defaultValue%20%3D%20'DEFAULT_VALUE'%0Aconst%20pathToSearch%20%3D%20'a.b'%0Aconst%20pathToSearchList%20%3D%20%5B'a'%2C%20'b'%5D%0A%0Aconst%20obj%20%3D%20%7B%0A%20%20a%20%3A%20%7B%0A%20%20%20%20b%20%3A%201%0A%20%20%7D%0A%7D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.pathOr(DEFAULT_VALUE%2C%20pathToSearch%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pathOr(DEFAULT_VALUE%2C%20pathToSearchList%2C%20Record%3Cstring%2C%20unknown%3E)%2C%20%0A%20%20R.pathOr(DEFAULT_VALUE%2C%20'a.b.c'%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5B1%2C%201%2C%20'DEFAULT_VALUE'%5D">Try this <strong>R.pathOr</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T;pathOr<T>(defaultValue: T, pathToSearch: Path): (obj: any) => T;pathOr<T>(defaultValue: T): (pathToSearch: Path) => (obj: any) => T;```
</details><details><summary><strong>R.pathOr</strong> source</summary>```javascriptimport { curry } from './curry.js'import { defaultTo } from './defaultTo.js'import { path } from './path.js'
function pathOrFn( defaultValue, pathInput, obj){ return defaultTo(defaultValue, path(pathInput, obj))}
export const pathOr = curry(pathOrFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { pathOr } from './pathOr.js'
test('with undefined', () => { const result = pathOr( 'foo', 'x.y', { x : { y : 1 } } ) expect(result).toBe(1)})
test('with null', () => { const result = pathOr( 'foo', 'x.y', null ) expect(result).toBe('foo')})
test('with NaN', () => { const result = pathOr( 'foo', 'x.y', NaN ) expect(result).toBe('foo')})
test('curry case (x)(y)(z)', () => { const result = pathOr('foo')('x.y.z')({ x : { y : { a : 1 } } }) expect(result).toBe('foo')})
test('curry case (x)(y,z)', () => { const result = pathOr('foo', 'x.y.z')({ x : { y : { a : 1 } } }) expect(result).toBe('foo')})
test('curry case (x,y)(z)', () => { const result = pathOr('foo')('x.y.z', { x : { y : { a : 1 } } }) expect(result).toBe('foo')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {pathOr} from 'rambda'
describe('R.pathOr', () => { it('with string path', () => { const x = pathOr<string>('foo', 'x.y', {x: {y: 'bar'}}) x // $ExpectType string }) it('with array path', () => { const x = pathOr<string>('foo', ['x', 'y'], {x: {y: 'bar'}}) x // $ExpectType string }) it('without passing type looks bad', () => { const x = pathOr('foo', 'x.y', {x: {y: 'bar'}}) x // $ExpectType "foo" }) it('curried', () => { const x = pathOr<string>('foo', 'x.y')({x: {y: 'bar'}}) x // $ExpectType string })})```
</details>[](#pathOr)
### paths
```typescript
paths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[]```
It loops over members of `pathsToSearch` as `singlePath` and returns the array produced by `R.path(singlePath, Record<string, unknown>)`.
Because it calls `R.path`, then `singlePath` can be either string or a list.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7B%0A%20%20a%20%3A%20%7B%0A%20%20%20%20b%20%3A%20%7B%0A%20%20%20%20%20%20c%20%3A%201%2C%0A%20%20%20%20%20%20d%20%3A%202%0A%20%20%20%20%7D%0A%20%20%7D%0A%7D%0A%0Aconst%20result%20%3D%20R.paths(%5B%0A%20%20'a.b.c'%2C%0A%20%20'a.b.d'%2C%0A%20%20'a.b.c.d.e'%2C%0A%5D%2C%20Record%3Cstring%2C%20unknown%3E)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%20undefined%5D">Try this <strong>R.paths</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpaths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[];paths<Input, T>(pathsToSearch: Path[]): (obj: Input) => (T | undefined)[];paths<T>(pathsToSearch: Path[], obj: any): (T | undefined)[];paths<T>(pathsToSearch: Path[]): (obj: any) => (T | undefined)[];```
</details><details><summary><strong>R.paths</strong> source</summary>```javascriptimport { path } from './path.js'
export function paths(pathsToSearch, obj){ if (arguments.length === 1){ return _obj => paths(pathsToSearch, _obj) } return pathsToSearch.map(singlePath => path(singlePath, obj))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { paths } from './paths.js'
const obj = { a : { b : { c : 1, d : 2, }, }, p : [ { q : 3 } ], x : { y : 'FOO', z : [ [ {} ] ], },}
test('with string path + curry', () => { const pathsInput = [ 'a.b.d', 'p.q' ] const expected = [ 2, undefined ] const result = paths(pathsInput, obj) const curriedResult = paths(pathsInput)(obj) expect(result).toEqual(expected) expect(curriedResult).toEqual(expected)})
test('with array path', () => { const result = paths([ [ 'a', 'b', 'c' ], [ 'x', 'y' ], ], obj) expect(result).toEqual([ 1, 'FOO' ])})
test('takes a paths that contains indices into arrays', () => { expect(paths([ [ 'p', 0, 'q' ], [ 'x', 'z', 0, 0 ], ], obj)).toEqual([ 3, {} ]) expect(paths([ [ 'p', 0, 'q' ], [ 'x', 'z', 2, 1 ], ], obj)).toEqual([ 3, undefined ])})
test('gets a deep property\'s value from objects', () => { expect(paths([ [ 'a', 'b' ] ], obj)).toEqual([ obj.a.b ]) expect(paths([ [ 'p', 0 ] ], obj)).toEqual([ obj.p[ 0 ] ])})
test('returns undefined for items not found', () => { expect(paths([ [ 'a', 'x', 'y' ] ], obj)).toEqual([ undefined ]) expect(paths([ [ 'p', 2 ] ], obj)).toEqual([ undefined ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {paths} from 'rambda'
interface Input { a: number, b: number, c: number,}
const input: Input = {a: 1, b: 2, c: 3}
describe('R.paths', () => { it('with dot notation', () => { const result = paths<number>(['a.b.c', 'foo.bar'], input) result // $ExpectType (number | undefined)[] }) it('without type', () => { const result = paths(['a.b.c', 'foo.bar'], input) result // $ExpectType unknown[] }) it('with array as path', () => { const result = paths<number>([['a', 'b', 'c'], ['foo.bar']], input) result // $ExpectType (number | undefined)[] }) it('curried', () => { const result = paths<number>([['a', 'b', 'c'], ['foo.bar']])(input) result // $ExpectType (number | undefined)[] })})```
</details>[](#paths)
### pathSatisfies
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.pathSatisfies(%0A%20%20x%20%3D%3E%20x%20%3E%200%2C%0A%20%20%5B'a'%2C%20'b'%2C%20'c'%5D%2C%0A%20%20%7Ba%3A%20%7Bb%3A%20%7Bc%3A%201%7D%7D%7D%0A)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.pathSatisfies</strong> example in Rambda REPL</a>[](#pathSatisfies)
### pick
```typescript
pick<T, K extends string | number | symbol>(propsToPick: K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>```
It returns a partial copy of an `input` containing only `propsToPick` properties.
`input` can be either an object or an array.
String annotation of `propsToPick` is one of the differences between `Rambda` and `Ramda`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7B%0A%20%20a%20%3A%201%2C%0A%20%20b%20%3A%20false%2C%0A%20%20foo%3A%20'cherry'%0A%7D%0Aconst%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20propsToPick%20%3D%20'a%2Cfoo'%0Aconst%20propsToPickList%20%3D%20%5B'a'%2C%20'foo'%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.pick(propsToPick%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pick(propsToPickList%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pick('a%2Cbar'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pick('bar'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pick(%5B0%2C%203%2C%205%5D%2C%20list)%2C%0A%20%20R.pick('0%2C3%2C5'%2C%20list)%2C%0A%5D%0A%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A1%2C%20foo%3A%20'cherry'%7D%2C%0A%20%20%7Ba%3A1%2C%20foo%3A%20'cherry'%7D%2C%0A%20%20%7Ba%3A1%7D%2C%0A%20%20%7B%7D%2C%0A%20%20%7B0%3A%201%2C%203%3A%204%7D%2C%0A%20%20%7B0%3A%201%2C%203%3A%204%7D%2C%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.pick</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpick<T, K extends string | number | symbol>(propsToPick: K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>;pick<K extends string | number | symbol>(propsToPick: K[]): <T>(input: T) => Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>;pick<T, U>(propsToPick: string, input: T): U;pick<T, U>(propsToPick: string): (input: T) => U;pick<T>(propsToPick: string, input: object): T;pick<T>(propsToPick: string): (input: object) => T;```
</details><details><summary><strong>R.pick</strong> source</summary>```javascriptimport { createPath } from './_internals/createPath.js'
export function pick(propsToPick, input){ if (arguments.length === 1) return _input => pick(propsToPick, _input) if (input === null || input === undefined){ return undefined } const keys = createPath(propsToPick, ',') const willReturn = {} let counter = 0 while (counter < keys.length){ if (keys[ counter ] in input){ willReturn[ keys[ counter ] ] = input[ keys[ counter ] ] } counter++ } return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { pick } from './pick.js'
const obj = { a : 1, b : 2, c : 3,}
test('props to pick is a string', () => { const result = pick('a,c', obj) const resultCurry = pick('a,c')(obj) const expectedResult = { a : 1, c : 3, } expect(result).toEqual(expectedResult) expect(resultCurry).toEqual(expectedResult)})
test('when prop is missing', () => { const result = pick('a,d,f', obj) expect(result).toEqual({ a : 1 })})
test('with list indexes as props', () => { const list = [ 1, 2, 3 ] const expected = { 0 : 1, 2 : 3, } expect(pick([ 0, 2, 3 ], list)).toEqual(expected) expect(pick('0,2,3', list)).toEqual(expected)})
test('props to pick is an array', () => { expect(pick([ 'a', 'c' ])({ a : 'foo', b : 'bar', c : 'baz', })).toEqual({ a : 'foo', c : 'baz', }) expect(pick([ 'a', 'd', 'e', 'f' ])({ a : 'foo', b : 'bar', c : 'baz', })).toEqual({ a : 'foo' }) expect(pick('a,d,e,f')(null)).toBeUndefined()})
test('works with list as input and number as props - props to pick is an array', () => { const result = pick([ 1, 2 ], [ 'a', 'b', 'c', 'd' ]) expect(result).toEqual({ 1 : 'b', 2 : 'c', })})
test('works with list as input and number as props - props to pick is a string', () => { const result = pick('1,2', [ 'a', 'b', 'c', 'd' ]) expect(result).toEqual({ 1 : 'b', 2 : 'c', })})
test('with symbol', () => { const symbolProp = Symbol('s') expect(pick([ symbolProp ], { [ symbolProp ] : 'a' })).toMatchInlineSnapshot(`{ Symbol(s): "a",}`)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {pick} from 'rambda'
const input = {a: 'foo', b: 2, c: 3, d: 4}
describe('R.pick with array as props input', () => { it('without passing type', () => { const result = pick(['a', 'c'], input) result.a // $ExpectType string result.c // $ExpectType number })})
describe('R.pick with string as props input', () => { interface Input { a: string, b: number, c: number, d: number, } interface Output { a: string, c: number, } it('explicitly declare output', () => { const result = pick<Output>('a,c', input) result // $ExpectType Output result.a // $ExpectType string result.c // $ExpectType number const curriedResult = pick<Output>('a,c')(input) curriedResult.a // $ExpectType string }) it('explicitly declare input and output', () => { const result = pick<Input, Output>('a,c', input) result // $ExpectType Output result.a // $ExpectType string const curriedResult = pick<Input, Output>('a,c')(input) curriedResult.a // $ExpectType string }) it('without passing type', () => { const result = pick('a,c', input) result // $ExpectType unknown })})```
</details>[](#pick)
### pickAll
```typescript
pickAll<T, K extends keyof T>(propsToPicks: K[], input: T): Pick<T, K>```
Same as `R.pick` but it won't skip the missing props, i.e. it will assign them to `undefined`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7B%0A%20%20a%20%3A%201%2C%0A%20%20b%20%3A%20false%2C%0A%20%20foo%3A%20'cherry'%0A%7D%0Aconst%20propsToPick%20%3D%20'a%2Cfoo%2Cbar'%0Aconst%20propsToPickList%20%3D%20%5B'a'%2C%20'foo'%2C%20'bar'%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.pickAll(propsToPick%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pickAll(propsToPickList%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pickAll('a%2Cbar'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.pickAll('bar'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%5D%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A1%2C%20foo%3A%20'cherry'%2C%20bar%3A%20undefined%7D%2C%0A%20%20%7Ba%3A1%2C%20foo%3A%20'cherry'%2C%20bar%3A%20undefined%7D%2C%0A%20%20%7Ba%3A1%2C%20bar%3A%20undefined%7D%2C%0A%20%20%7Bbar%3A%20undefined%7D%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.pickAll</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpickAll<T, K extends keyof T>(propsToPicks: K[], input: T): Pick<T, K>;pickAll<T, U>(propsToPicks: string[], input: T): U;pickAll(propsToPicks: string[]): <T, U>(input: T) => U;pickAll<T, U>(propsToPick: string, input: T): U;pickAll<T, U>(propsToPick: string): (input: T) => U;```
</details><details><summary><strong>R.pickAll</strong> source</summary>```javascriptimport { createPath } from './_internals/createPath.js'
export function pickAll(propsToPick, obj){ if (arguments.length === 1) return _obj => pickAll(propsToPick, _obj) if (obj === null || obj === undefined){ return undefined } const keysValue = createPath(propsToPick, ',') const willReturn = {} let counter = 0 while (counter < keysValue.length){ if (keysValue[ counter ] in obj){ willReturn[ keysValue[ counter ] ] = obj[ keysValue[ counter ] ] } else { willReturn[ keysValue[ counter ] ] = undefined } counter++ } return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { pickAll } from './pickAll.js'
test('when input is undefined or null', () => { expect(pickAll('a', null)).toBeUndefined() expect(pickAll('a', undefined)).toBeUndefined()})
test('with string as condition', () => { const obj = { a : 1, b : 2, c : 3, } const result = pickAll('a,c', obj) const resultCurry = pickAll('a,c')(obj) const expectedResult = { a : 1, b : undefined, c : 3, } expect(result).toEqual(expectedResult) expect(resultCurry).toEqual(expectedResult)})
test('with array as condition', () => { expect(pickAll([ 'a', 'b', 'c' ], { a : 'foo', c : 'baz', })).toEqual({ a : 'foo', b : undefined, c : 'baz', })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {pickAll} from 'rambda'
interface Input { a: string, b: number, c: number, d: number,}interface Output { a?: string, c?: number,}const input = {a: 'foo', b: 2, c: 3, d: 4}
describe('R.pickAll with array as props input', () => { it('without passing type', () => { const result = pickAll(['a', 'c'], input) result.a // $ExpectType string result.c // $ExpectType number }) it('without passing type + curry', () => { const result = pickAll(['a', 'c'])(input) result // $ExpectType unknown }) it('explicitly passing types', () => { const result = pickAll<Input, Output>(['a', 'c'], input) result.a // $ExpectType string | undefined result.c // $ExpectType number | undefined })})
describe('R.pickAll with string as props input', () => { it('without passing type', () => { const result = pickAll('a,c', input) result // $ExpectType unknown }) it('without passing type + curry', () => { const result = pickAll('a,c')(input) result // $ExpectType unknown }) it('explicitly passing types', () => { const result = pickAll<Input, Output>('a,c', input) result.a // $ExpectType string | undefined result.c // $ExpectType number | undefined }) it('explicitly passing types + curry', () => { const result = pickAll<Input, Output>('a,c')(input) result.a // $ExpectType string | undefined result.c // $ExpectType number | undefined })})```
</details>[](#pickAll)
### pickBy
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.pickBy(%0A%20%20x%20%3D%3E%20x%20%3E%201%2C%0A%20%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D%0A)%0A%2F%2F%20%3D%3E%20%7Bb%3A%202%2C%20c%3A%203%7D">Try this <strong>R.pickBy</strong> example in Rambda REPL</a>[](#pickBy)
### pipe
It performs left-to-right function composition.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.pipe(%0A%20%20R.filter(val%20%3D%3E%20val%20%3E%202)%2C%0A%20%20R.map(a%20%3D%3E%20a%20*%202)%0A)(%5B1%2C%202%2C%203%2C%204%5D)%0A%0A%2F%2F%20%3D%3E%20%5B6%2C%208%5D">Try this <strong>R.pipe</strong> example in Rambda REPL</a>[](#pipe)
### pluck
```typescript
pluck<K extends keyof T, T>(property: K, list: T[]): T[K][]```
It returns list of the values of `property` taken from the all objects inside `list`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%7Ba%3A%201%7D%2C%20%7Ba%3A%202%7D%2C%20%7Bb%3A%203%7D%5D%0Aconst%20property%20%3D%20'a'%0A%0Aconst%20result%20%3D%20R.pluck(property%2C%20list)%20%0A%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.pluck</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpluck<K extends keyof T, T>(property: K, list: T[]): T[K][];pluck<T>(property: number, list: { [k: number]: T }[]): T[];pluck<P extends string>(property: P): <T>(list: Record<P, T>[]) => T[];pluck(property: number): <T>(list: { [k: number]: T }[]) => T[];```
</details><details><summary><strong>R.pluck</strong> source</summary>```javascriptimport { map } from './map.js'
export function pluck(property, list){ if (arguments.length === 1) return _list => pluck(property, _list) const willReturn = [] map(x => { if (x[ property ] !== undefined){ willReturn.push(x[ property ]) } }, list) return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { pluck } from './pluck.js'
test('happy', () => { expect(pluck('a')([ { a : 1 }, { a : 2 }, { b : 1 } ])).toEqual([ 1, 2 ])})
test('with undefined', () => { expect(pluck(undefined)([ { a : 1 }, { a : 2 }, { b : 1 } ])).toEqual([ ])})
test('with number', () => { const input = [ [ 1, 2 ], [ 3, 4 ], ] expect(pluck(0, input)).toEqual([ 1, 3 ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {pluck} from 'rambda'
describe('R.pluck', () => { it('with object', () => { interface ListMember { a: number, b: string, } const input: ListMember[] = [ {a: 1, b: 'foo'}, {a: 2, b: 'bar'}, ] const resultA = pluck('a', input) const resultB = pluck('b')(input) resultA // $ExpectType number[] resultB // $ExpectType string[] }) it('with array', () => { const input = [ [1, 2], [3, 4], [5, 6], ] const result = pluck(0, input) const resultCurry = pluck(0)(input) result // $ExpectType number[] resultCurry // $ExpectType number[] })})```
</details>[](#pluck)
### prepend
```typescript
prepend<T>(xToPrepend: T, iterable: T[]): T[]```
It adds element `x` at the beginning of `list`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.prepend('foo'%2C%20%5B'bar'%2C%20'baz'%5D)%0A%2F%2F%20%3D%3E%20%5B'foo'%2C%20'bar'%2C%20'baz'%5D">Try this <strong>R.prepend</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptprepend<T>(xToPrepend: T, iterable: T[]): T[];prepend<T, U>(xToPrepend: T, iterable: IsFirstSubtypeOfSecond<T, U>[]) : U[];prepend<T>(xToPrepend: T): <U>(iterable: IsFirstSubtypeOfSecond<T, U>[]) => U[];prepend<T>(xToPrepend: T): (iterable: T[]) => T[];```
</details><details><summary><strong>R.prepend</strong> source</summary>```javascriptexport function prepend(x, input){ if (arguments.length === 1) return _input => prepend(x, _input) if (typeof input === 'string') return [ x ].concat(input.split('')) return [ x ].concat(input)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { prepend } from './prepend.js'
test('happy', () => { expect(prepend('yes', [ 'foo', 'bar', 'baz' ])).toEqual([ 'yes', 'foo', 'bar', 'baz', ])})
test('with empty list', () => { expect(prepend('foo')([])).toEqual([ 'foo' ])})
test('with string instead of array', () => { expect(prepend('foo')('bar')).toEqual([ 'foo', 'b', 'a', 'r' ])})```
</details>[](#prepend)
### product
```typescript
product(list: number[]): number```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.product(%5B%202%2C%203%2C%204%20%5D)%0A%2F%2F%20%3D%3E%2024)">Try this <strong>R.product</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptproduct(list: number[]): number;```
</details><details><summary><strong>R.product</strong> source</summary>```javascriptimport { multiply } from './multiply.js'import { reduce } from './reduce.js'
export const product = reduce(multiply, 1)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { product } from './product.js'
test('happy', () => { expect(product([ 2, 3, 4 ])).toBe(24)})
test('bad input', () => { expect(product([ null ])).toBe(0) expect(product([])).toBe(1)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {product} from 'rambda'
describe('R.product', () => { it('happy', () => { const result = product([1, 2, 3]) result // $ExpectType number })})```
</details>[](#product)
### prop
```typescript
prop<_, P extends keyof never, T>(p: P, value: T): Prop<T, P>```
It returns the value of property `propToFind` in `obj`.
If there is no such property, it returns `undefined`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.prop('x'%2C%20%7Bx%3A%20100%7D)%2C%20%0A%20%20R.prop('x'%2C%20%7Ba%3A%201%7D)%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B100%2C%20undefined%5D">Try this <strong>R.prop</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptprop<_, P extends keyof never, T>(p: P, value: T): Prop<T, P>;prop<V>(p: keyof never, value: unknown): V;prop<_, P extends keyof never>(p: P): <T>(value: T) => Prop<T, P>;prop<V>(p: keyof never): (value: unknown) => V;```
</details><details><summary><strong>R.prop</strong> source</summary>```javascriptexport function propFn(searchProperty, obj){ if (!obj) return undefined return obj[ searchProperty ]}
export function prop(searchProperty, obj){ if (arguments.length === 1) return _obj => prop(searchProperty, _obj) return propFn(searchProperty, obj)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { prop } from './prop.js'
test('prop', () => { expect(prop('foo')({ foo : 'baz' })).toBe('baz') expect(prop('bar')({ foo : 'baz' })).toBeUndefined() expect(prop('bar')(null)).toBeUndefined()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {prop} from 'rambda'
describe('R.prop', () => { interface Foo { a: number, b: string, c?: number, } const obj: Foo = {a: 1, b: 'foo'} it('issue #553', () => { const result = { a: prop('a', obj), b: prop('b', obj), c: prop('c', obj), } const curriedResult = { a: prop('a')(obj), b: prop('b')(obj), c: prop('c')(obj), } result // $ExpectType { a: number; b: string; c: number | undefined; } curriedResult // $ExpectType { a: number; b: string; c: number | undefined; } })})
describe('with number as prop', () => { const list = [1, 2, 3] const index = 1 it('happy', () => { const result = prop(index, list) result // $ExpectType number }) it('curried require explicit type', () => { const result = prop<number>(index)(list) result // $ExpectType number })})```
</details>[](#prop)
### propEq
```typescript
propEq<K extends string | number>(valueToMatch: any, propToFind: K, obj: Record<K, any>): boolean```
It returns true if `obj` has property `propToFind` and its value is equal to `valueToMatch`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7B%20foo%3A%20'bar'%20%7D%0Aconst%20secondObj%20%3D%20%7B%20foo%3A%201%20%7D%0A%0Aconst%20propToFind%20%3D%20'foo'%0Aconst%20valueToMatch%20%3D%20'bar'%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.propEq(propToFind%2C%20valueToMatch%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.propEq(propToFind%2C%20valueToMatch%2C%20secondRecord%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.propEq</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpropEq<K extends string | number>(valueToMatch: any, propToFind: K, obj: Record<K, any>): boolean;propEq<K extends string | number>(valueToMatch: any, propToFind: K): (obj: Record<K, any>) => boolean;propEq(valueToMatch: any): { <K extends string | number>(propToFind: K, obj: Record<K, any>): boolean; <K extends string | number>(propToFind: K): (obj: Record<K, any>) => boolean;};```
</details><details><summary><strong>R.propEq</strong> source</summary>```javascriptimport { curry } from './curry.js'import { equals } from './equals.js'import { prop } from './prop.js'
function propEqFn( valueToMatch, propToFind, obj){ if (!obj) return false return equals(valueToMatch, prop(propToFind, obj))}
export const propEq = curry(propEqFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { BAR, FOO } from './_internals/testUtils.js'import { propEq } from './propEq.js'
test('happy', () => { const obj = { [ FOO ] : BAR } expect(propEq(BAR, FOO)(obj)).toBeTrue() expect(propEq(1, FOO)(obj)).toBeFalse() expect(propEq(1)(FOO)(obj)).toBeFalse() expect(propEq( 1, 1, null )).toBeFalse()})
test('returns false if called with a null or undefined object', () => { expect(propEq( 'name', 'Abby', null )).toBeFalse() expect(propEq( 'name', 'Abby', undefined )).toBeFalse()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {propEq} from 'rambda'
const property = 'foo'const numberProperty = 1const value = 'bar'const obj = {[property]: value}const objWithNumberIndex = {[numberProperty]: value}
describe('R.propEq', () => { it('happy', () => { const result = propEq(value, property, obj) result // $ExpectType boolean }) it('number is property', () => { const result = propEq(value, 1, objWithNumberIndex) result // $ExpectType boolean }) it('with optional property', () => { interface MyType { optional?: string | number, } const myObject: MyType = {} const valueToFind = '1111' // @ts-expect-error propEq(valueToFind, 'optional', myObject) }) it('imported from @types/ramda', () => { interface A { foo: string | null, } const obj: A = { foo: 'bar', } const value = '' const result = propEq(value, 'foo')(obj) result // $ExpectType boolean // @ts-expect-error propEq(value, 'bar')(obj) })})```
</details>[](#propEq)
### propIs
```typescript
propIs<C extends AnyFunction, K extends keyof any>(type: C, name: K, obj: any): obj is Record<K, ReturnType<C>>```
It returns `true` if `property` of `obj` is from `target` type.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A1%2C%20b%3A%20'foo'%7D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.propIs(Number%2C%20'a'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.propIs(String%2C%20'b'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.propIs(Number%2C%20'b'%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%2C%20false%5D">Try this <strong>R.propIs</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpropIs<C extends AnyFunction, K extends keyof any>(type: C, name: K, obj: any): obj is Record<K, ReturnType<C>>;propIs<C extends AnyConstructor, K extends keyof any>(type: C, name: K, obj: any): obj is Record<K, InstanceType<C>>;propIs<C extends AnyFunction, K extends keyof any>(type: C, name: K): (obj: any) => obj is Record<K, ReturnType<C>>;propIs<C extends AnyConstructor, K extends keyof any>(type: C, name: K): (obj: any) => obj is Record<K, InstanceType<C>>;propIs<C extends AnyFunction>(type: C): { <K extends keyof any>(name: K, obj: any): obj is Record<K, ReturnType<C>>; <K extends keyof any>(name: K): (obj: any) => obj is Record<K, ReturnType<C>>;};```
</details><details><summary><strong>R.propIs</strong> source</summary>```javascriptimport { curry } from './curry.js'import { is } from './is.js'
function propIsFn( targetPrototype, property, obj){ return is(targetPrototype, obj[ property ])}
export const propIs = curry(propIsFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { propIs } from './propIs.js'
const obj = { a : 1, b : 'foo',}
test('when true', () => { expect(propIs( Number, 'a', obj )).toBeTrue() expect(propIs( String, 'b', obj )).toBeTrue()})
test('when false', () => { expect(propIs( String, 'a', obj )).toBeFalse() expect(propIs( Number, 'b', obj )).toBeFalse()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {propIs} from 'rambda'
const property = 'a'const obj = {a: 1}
describe('R.propIs', () => { it('happy', () => { const result = propIs(Number, property, obj) result // $ExpectType boolean }) it('curried', () => { const result = propIs(Number, property)(obj) result // $ExpectType boolean })})```
</details>[](#propIs)
### propOr
```typescript
propOr<T, P extends string>(defaultValue: T, property: P, obj: Partial<Record<P, T>> | undefined): T```
It returns either `defaultValue` or the value of `property` in `obj`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%201%7D%0Aconst%20defaultValue%20%3D%20'DEFAULT_VALUE'%0Aconst%20property%20%3D%20'a'%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.propOr(defaultValue%2C%20property%2C%20Record%3Cstring%2C%20unknown%3E)%2C%0A%20%20R.propOr(defaultValue%2C%20'foo'%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5B1%2C%20'DEFAULT_VALUE'%5D">Try this <strong>R.propOr</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpropOr<T, P extends string>(defaultValue: T, property: P, obj: Partial<Record<P, T>> | undefined): T;propOr<T, P extends string>(defaultValue: T, property: P): (obj: Partial<Record<P, T>> | undefined) => T;propOr<T>(defaultValue: T): { <P extends string>(property: P, obj: Partial<Record<P, T>> | undefined): T; <P extends string>(property: P): (obj: Partial<Record<P, T>> | undefined) => T;}```
</details><details><summary><strong>R.propOr</strong> source</summary>```javascriptimport { curry } from './curry.js'import { defaultTo } from './defaultTo.js'
function propOrFn( defaultValue, property, obj){ if (!obj) return defaultValue return defaultTo(defaultValue, obj[ property ])}
export const propOr = curry(propOrFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { propOr } from './propOr.js'
test('propOr (result)', () => { const obj = { a : 1 } expect(propOr( 'default', 'a', obj )).toBe(1) expect(propOr( 'default', 'notExist', obj )).toBe('default') expect(propOr( 'default', 'notExist', null )).toBe('default')})
test('propOr (currying)', () => { const obj = { a : 1 } expect(propOr('default')('a', obj)).toBe(1) expect(propOr('default', 'a')(obj)).toBe(1) expect(propOr('default')('notExist', obj)).toBe('default') expect(propOr('default', 'notExist')(obj)).toBe('default')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {propOr} from 'rambda'
const obj = {foo: 'bar'}const property = 'foo'const fallback = 'fallback'
describe('R.propOr', () => { it('happy', () => { const result = propOr(fallback, property, obj) result // $ExpectType string }) it('curry 1', () => { const result = propOr(fallback)(property, obj) result // $ExpectType string }) it('curry 2', () => { const result = propOr(fallback, property)(obj) result // $ExpectType string }) it('curry 3', () => { const result = propOr(fallback)(property)(obj) result // $ExpectType string })})```
</details>[](#propOr)
### props
```typescript
props<P extends string, T>(propsToPick: P[], obj: Record<P, T>): T[]```
It takes list with properties `propsToPick` and returns a list with property values in `obj`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.props(%0A%20%20%5B'a'%2C%20'b'%5D%2C%20%0A%20%20%7Ba%3A1%2C%20c%3A3%7D%0A)%0A%2F%2F%20%3D%3E%20%5B1%2C%20undefined%5D">Try this <strong>R.props</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptprops<P extends string, T>(propsToPick: P[], obj: Record<P, T>): T[];props<P extends string>(propsToPick: P[]): <T>(obj: Record<P, T>) => T[];props<P extends string, T>(propsToPick: P[]): (obj: Record<P, T>) => T[];```
</details><details><summary><strong>R.props</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'import { mapArray } from './map.js'
export function props(propsToPick, obj){ if (arguments.length === 1){ return _obj => props(propsToPick, _obj) } if (!isArray(propsToPick)){ throw new Error('propsToPick is not a list') } return mapArray(prop => obj[ prop ], propsToPick)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { props } from './props.js'
const obj = { a : 1, b : 2,}const propsToPick = [ 'a', 'c' ]
test('happy', () => { const result = props(propsToPick, obj) expect(result).toEqual([ 1, undefined ])})
test('curried', () => { const result = props(propsToPick)(obj) expect(result).toEqual([ 1, undefined ])})
test('wrong input', () => { expect(() => props(null)(obj)).toThrowErrorMatchingInlineSnapshot('"propsToPick is not a list"')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {props} from 'rambda'
const obj = {a: 1, b: 2}
describe('R.props', () => { it('happy', () => { const result = props(['a', 'b'], obj) result // $ExpectType number[] }) it('curried', () => { const result = props(['a', 'b'])(obj) result // $ExpectType number[] })})```
</details>[](#props)
### propSatisfies
```typescript
propSatisfies<T>(predicate: Predicate<T>, property: string, obj: Record<string, T>): boolean```
It returns `true` if the object property satisfies a given predicate.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A%20%7Bb%3A1%7D%7D%0Aconst%20property%20%3D%20'a'%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%3F.b%20%3D%3D%3D%201%0A%0Aconst%20result%20%3D%20R.propSatisfies(predicate%2C%20property%2C%20Record%3Cstring%2C%20unknown%3E)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.propSatisfies</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptpropSatisfies<T>(predicate: Predicate<T>, property: string, obj: Record<string, T>): boolean;propSatisfies<T>(predicate: Predicate<T>, property: string): (obj: Record<string, T>) => boolean;```
</details><details><summary><strong>R.propSatisfies</strong> source</summary>```javascriptimport { curry } from './curry.js'import { prop } from './prop.js'
function propSatisfiesFn( predicate, property, obj){ return predicate(prop(property, obj))}
export const propSatisfies = curry(propSatisfiesFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { propSatisfies } from './propSatisfies.js'
const obj = { a : 1 }
test('when true', () => { expect(propSatisfies( x => x > 0, 'a', obj )).toBeTrue()})
test('when false', () => { expect(propSatisfies(x => x < 0, 'a')(obj)).toBeFalse()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {propSatisfies} from 'rambda'
const obj = {a: 1}
describe('R.propSatisfies', () => { it('happy', () => { const result = propSatisfies(x => x > 0, 'a', obj) result // $ExpectType boolean }) it('curried requires explicit type', () => { const result = propSatisfies<number>(x => x > 0, 'a')(obj) result // $ExpectType boolean })})```
</details>[](#propSatisfies)
### range
```typescript
range(startInclusive: number, endExclusive: number): number[]```
It returns list of numbers between `startInclusive` to `endExclusive` markers.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.range(0%2C%205)%0A%2F%2F%20%3D%3E%20%5B0%2C%201%2C%202%2C%203%2C%204%5D">Try this <strong>R.range</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptrange(startInclusive: number, endExclusive: number): number[];range(startInclusive: number): (endExclusive: number) => number[];```
</details><details><summary><strong>R.range</strong> source</summary>```javascriptexport function range(start, end){ if (arguments.length === 1) return _end => range(start, _end) if (Number.isNaN(Number(start)) || Number.isNaN(Number(end))){ throw new TypeError('Both arguments to range must be numbers') } if (end < start) return [] const len = end - start const willReturn = Array(len) for (let i = 0; i < len; i++){ willReturn[ i ] = start + i } return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { range } from './range.js'
test('happy', () => { expect(range(0, 10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])})
test('end range is bigger than start range', () => { expect(range(7, 3)).toEqual([]) expect(range(5, 5)).toEqual([])})
test('with bad input', () => { const throwMessage = 'Both arguments to range must be numbers' expect(() => range('a', 6)).toThrowWithMessage(Error, throwMessage) expect(() => range(6, 'z')).toThrowWithMessage(Error, throwMessage)})
test('curry', () => { expect(range(0)(10)).toEqual([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {range} from 'rambda'
describe('R.range', () => { it('happy', () => { const result = range(1, 4) result // $ExpectType number[] }) it('curried', () => { const result = range(1)(4) result // $ExpectType number[] })})```
</details>[](#range)
### reduce
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0Aconst%20initialValue%20%3D%2010%0Aconst%20reducer%20%3D%20(prev%2C%20current)%20%3D%3E%20prev%20*%20current%0A%0Aconst%20result%20%3D%20R.reduce(reducer%2C%20initialValue%2C%20list)%0A%2F%2F%20%3D%3E%2060">Try this <strong>R.reduce</strong> example in Rambda REPL</a>[](#reduce)
### reduceBy
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.reduceBy(%0A%20%20(acc%2C%20elem)%20%3D%3E%20acc%20%2B%20elem%2C%0A%20%200%2C%0A%20%20x%20%3D%3E%20x%20%3E%202%20%3F%20'big'%20%3A%20'small'%2C%0A%20%20%5B1%2C%202%2C%203%2C%204%2C%205%5D%0A)%0A%2F%2F%20%3D%3E%20%7B%20big%3A%2012%2C%20small%3A%203%20%7D">Try this <strong>R.reduceBy</strong> example in Rambda REPL</a>[](#reduceBy)
### reject
```typescript
reject<T>(predicate: Predicate<T>, list: T[]): T[]```
It has the opposite effect of `R.filter`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20obj%20%3D%20%7Ba%3A%201%2C%20b%3A%202%7D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3E%201%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.reject(predicate%2C%20list)%2C%0A%20%20R.reject(predicate%2C%20Record%3Cstring%2C%20unknown%3E)%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B1%5D%2C%20%7Ba%3A%201%7D%5D">Try this <strong>R.reject</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptreject<T>(predicate: Predicate<T>, list: T[]): T[];reject<T>(predicate: Predicate<T>): (list: T[]) => T[];reject<T>(predicate: Predicate<T>, obj: Dictionary<T>): Dictionary<T>;reject<T, U>(predicate: Predicate<T>): (obj: Dictionary<T>) => Dictionary<T>;```
</details><details><summary><strong>R.reject</strong> source</summary>```javascriptimport { filter } from './filter.js'
export function reject(predicate, list){ if (arguments.length === 1) return _list => reject(predicate, _list) return filter(x => !predicate(x), list)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { reject } from './reject.js'
const isOdd = n => n % 2 === 1
test('with array', () => { expect(reject(isOdd)([ 1, 2, 3, 4 ])).toEqual([ 2, 4 ])})
test('with object', () => { const obj = { a : 1, b : 2, c : 3, d : 4, } expect(reject(isOdd, obj)).toEqual({ b : 2, d : 4, })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {reject} from 'rambda'
describe('R.reject with array', () => { it('happy', () => { const result = reject( x => { x // $ExpectType number return x > 1 }, [1, 2, 3] ) result // $ExpectType number[] }) it('curried require explicit type', () => { const result = reject<number>(x => { x // $ExpectType number return x > 1 })([1, 2, 3]) result // $ExpectType number[] })})
describe('R.reject with objects', () => { it('happy', () => { const result = reject( x => { x // $ExpectType number return x > 1 }, {a: 1, b: 2} ) result // $ExpectType Dictionary<number> }) it('curried require dummy type', () => { const result = reject<number, any>(x => { return x > 1 })({a: 1, b: 2}) result // $ExpectType Dictionary<number> })})```
</details>[](#reject)
### removeIndex
```typescript
removeIndex<T>(index: number, list: T[]): T[]```
It returns a copy of `list` input with removed `index`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20result%20%3D%20R.removeIndex(1%2C%20list)%0A%2F%2F%20%3D%3E%20%5B1%2C%203%2C%204%5D">Try this <strong>R.removeIndex</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptremoveIndex<T>(index: number, list: T[]): T[];removeIndex(index: number): <T>(list: T[]) => T[];```
</details><details><summary><strong>R.removeIndex</strong> source</summary>```javascriptexport function removeIndex(index, list){ if (arguments.length === 1) return _list => removeIndex(index, _list) if (index <= 0) return list.slice(1) if (index >= list.length - 1) return list.slice(0, list.length - 1) return [ ...list.slice(0, index), ...list.slice(index + 1) ]}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { removeIndex } from './removeIndex.js'
const list = [ 1, 2, 3, 4 ]
test('first or before first index', () => { expect(removeIndex(-2, list)).toEqual([ 2, 3, 4 ]) expect(removeIndex(-2)(list)).toEqual([ 2, 3, 4 ])})
test('last or after last index', () => { expect(removeIndex(4, list)).toEqual([ 1, 2, 3 ]) expect(removeIndex(10, list)).toEqual([ 1, 2, 3 ])})
test('middle index', () => { expect(removeIndex(1, list)).toEqual([ 1, 3, 4 ]) expect(removeIndex(2, list)).toEqual([ 1, 2, 4 ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {removeIndex} from 'rambda'
describe('R.removeIndex', () => { it('happy', () => { const result = removeIndex(1, [1, 2, 3]) result // $ExpectType number[] }) it('curried', () => { const result = removeIndex(1)([1, 2, 3]) result // $ExpectType number[] })})```
</details>[](#removeIndex)
### repeat
```typescript
repeat<T>(x: T): (timesToRepeat: number) => T[]```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.repeat('foo'%2C%203)%0A%2F%2F%20%3D%3E%20%5B'foo'%2C%20'foo'%2C%20'foo'%5D">Try this <strong>R.repeat</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptrepeat<T>(x: T): (timesToRepeat: number) => T[];repeat<T>(x: T, timesToRepeat: number): T[];```
</details><details><summary><strong>R.repeat</strong> source</summary>```javascriptexport function repeat(x, timesToRepeat){ if (arguments.length === 1){ return _timesToRepeat => repeat(x, _timesToRepeat) } return Array(timesToRepeat).fill(x)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { repeat } from './repeat.js'
test('repeat', () => { expect(repeat('')(3)).toEqual([ '', '', '' ]) expect(repeat('foo', 3)).toEqual([ 'foo', 'foo', 'foo' ]) const obj = {} const arr = repeat(obj, 3) expect(arr).toEqual([ {}, {}, {} ]) expect(arr[ 0 ] === arr[ 1 ]).toBeTrue()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {repeat} from 'rambda'
describe('R.repeat', () => { it('happy', () => { const result = repeat(4, 7) result // $ExpectType number[] }) it('curried', () => { const result = repeat(4)(7) result // $ExpectType number[] })})```
</details>[](#repeat)
### replace
```typescript
replace(strOrRegex: RegExp | string, replacer: RegExpReplacer, str: string): string```
It replaces `strOrRegex` found in `str` with `replacer`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20strOrRegex%20%3D%20%2Fo%2Fg%0A%0Aconst%20result%20%3D%20R.replace(strOrRegex%2C%20'%7C0%7C'%2C%20'foo')%0A%2F%2F%20%3D%3E%20'f%7C0%7C%7C0%7C'">Try this <strong>R.replace</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptreplace(strOrRegex: RegExp | string, replacer: RegExpReplacer, str: string): string;replace(strOrRegex: RegExp | string, replacer: RegExpReplacer): (str: string) => string;replace(strOrRegex: RegExp | string): (replacer: RegExpReplacer) => (str: string) => string;```
</details><details><summary><strong>R.replace</strong> source</summary>```javascriptimport { curry } from './curry.js'
function replaceFn( pattern, replacer, str){ return str.replace(pattern, replacer)}
export const replace = curry(replaceFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { replace } from './replace.js'
test('happy', () => { expect(replace( /\s/g, '|', 'foo bar baz' )).toBe('foo|bar|baz')})
test('with function as replacer input', () => { expect(replace( /\s/g, ( match, offset, str ) => { expect(match).toBe(' ') expect([ 3, 7 ].includes(offset)).toBeTrue() expect(str).toBe('foo bar baz') return '|' }, 'foo bar baz' )).toBe('foo|bar|baz')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {replace} from 'rambda'
const str = 'foo bar foo'const replacer = 'bar'
describe('R.replace', () => { it('happy', () => { const result = replace(/foo/g, replacer, str) result // $ExpectType string }) it('with string as search pattern', () => { const result = replace('foo', replacer, str) result // $ExpectType string }) it('with function as replacer', () => { const result = replace('f(o)o', (m: string, p1: string, offset: number) => { m // $ExpectType string p1 // $ExpectType string offset // $ExpectType number return p1 }, str) result // $ExpectType string })})
describe('R.replace - curried', () => { it('happy', () => { const result = replace(/foo/g, replacer)(str) result // $ExpectType string }) it('with string as search pattern', () => { const result = replace('foo', replacer)(str) result // $ExpectType string }) it('with function as replacer', () => { const result = replace('f(o)o')((m: string, p1: string, offset: number) => { m // $ExpectType string p1 // $ExpectType string offset // $ExpectType number return p1 })(str) result // $ExpectType string })})```
</details>[](#replace)
### reverse
```typescript
reverse<T>(input: T[]): T[]```
It returns a reversed copy of list or string `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.reverse('foo')%2C%0A%20%20R.reverse(%5B1%2C%202%2C%203%5D)%0A%5D%0A%2F%2F%20%3D%3E%20%5B'oof'%2C%20%5B3%2C%202%2C%201%5D">Try this <strong>R.reverse</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptreverse<T>(input: T[]): T[];reverse(input: string): string;```
</details><details><summary><strong>R.reverse</strong> source</summary>```javascriptexport function reverse(listOrString) { if (typeof listOrString === 'string') { return listOrString.split('').reverse().join('') } const clone = listOrString.slice() return clone.reverse()}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport {reverse} from './reverse.js'
test('happy', () => { expect(reverse([1, 2, 3])).toEqual([3, 2, 1])})
test('with string', () => { expect(reverse('baz')).toBe('zab')})
test("it doesn't mutate", () => { const arr = [1, 2, 3] expect(reverse(arr)).toEqual([3, 2, 1]) expect(arr).toEqual([1, 2, 3])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {reverse} from 'rambda'
const list = [1, 2, 3, 4, 5]
describe('R.reverse', () => { it('happy', () => { const result = reverse(list) result // $ExpectType number[] })})```
</details>[](#reverse)
### set
```typescript
set<S, A>(lens: Lens<S, A>): { (a: A): (obj: S) => S (a: A, obj: S): S}```
It returns a copied **Object** or **Array** with modified `lens` focus set to `replacer` value.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20input%20%3D%20%7Bx%3A%201%2C%20y%3A%202%7D%0Aconst%20xLens%20%3D%20R.lensProp('x')%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.set(xLens%2C%204%2C%20input)%2C%0A%20%20R.set(xLens%2C%208%2C%20input)%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B%7Bx%3A%204%2C%20y%3A%202%7D%2C%20%7Bx%3A%208%2C%20y%3A%202%7D%5D">Try this <strong>R.set</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptset<S, A>(lens: Lens<S, A>): { (a: A): (obj: S) => S (a: A, obj: S): S};set<S, A>(lens: Lens<S, A>, a: A): (obj: S) => S;set<S, A>(lens: Lens<S, A>, a: A, obj: S): S;```
</details><details><summary><strong>R.set</strong> source</summary>```javascriptimport {always} from './always.js'import {curry} from './curry.js'import {over} from './over.js'
function setFn(lens, replacer, x) { return over(lens, always(replacer), x)}
export const set = curry(setFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport {assoc} from './assoc.js'import {lens} from './lens.js'import {lensIndex} from './lensIndex.js'import {lensPath} from './lensPath.js'import {prop} from './prop.js'import {set} from './set.js'
const testObject = { foo: 'bar', baz: { a: 'x', b: 'y', },}
test('assoc lens', () => { const assocLens = lens(prop('foo'), assoc('foo')) const result = set(assocLens, 'FOO', testObject) const expected = { ...testObject, foo: 'FOO', } expect(result).toEqual(expected)})
test('path lens', () => { const pathLens = lensPath('baz.a') const result = set(pathLens, 'z', testObject) const expected = { ...testObject, baz: { a: 'z', b: 'y', }, } expect(result).toEqual(expected)})
test('index lens', () => { const indexLens = lensIndex(0) const result = set(indexLens, 3, [1, 2]) expect(result).toEqual([3, 2])})```
</details>[](#set)
### slice
```typescript
slice(from: number, to: number, input: string): string```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B0%2C%201%2C%202%2C%203%2C%204%2C%205%5D%0Aconst%20str%20%3D%20'FOO_BAR'%0Aconst%20from%20%3D%201%0Aconst%20to%20%3D%204%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.slice(from%2C%20to%2C%20str)%2C%0A%20%20R.slice(from%2C%20to%2C%20list)%0A%5D%0A%2F%2F%20%3D%3E%20%5B'OO_'%2C%20%5B1%2C%202%2C%203%5D%5D">Try this <strong>R.slice</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptslice(from: number, to: number, input: string): string;slice<T>(from: number, to: number, input: T[]): T[];slice(from: number, to: number): { (input: string): string; <T>(input: T[]): T[];};slice(from: number): { (to: number, input: string): string; <T>(to: number, input: T[]): T[];};```
</details><details><summary><strong>R.slice</strong> source</summary>```javascriptimport { curry } from './curry.js'
function sliceFn( from, to, list){ return list.slice(from, to)}
export const slice = curry(sliceFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { slice } from './slice.js'
test('slice', () => { expect(slice( 1, 3, [ 'a', 'b', 'c', 'd' ] )).toEqual([ 'b', 'c' ]) expect(slice( 1, Infinity, [ 'a', 'b', 'c', 'd' ] )).toEqual([ 'b', 'c', 'd' ]) expect(slice( 0, -1, [ 'a', 'b', 'c', 'd' ] )).toEqual([ 'a', 'b', 'c' ]) expect(slice( -3, -1, [ 'a', 'b', 'c', 'd' ] )).toEqual([ 'b', 'c' ]) expect(slice( 0, 3, 'ramda' )).toBe('ram')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {slice} from 'rambda'
const list = [1, 2, 3, 4, 5]
describe('R.slice', () => { it('happy', () => { const result = slice(1, 3, list) result // $ExpectType number[] }) it('curried', () => { const result = slice(1, 3)(list) result // $ExpectType number[] })})```
</details>[](#slice)
### sort
```typescript
sort<T>(sortFn: (a: T, b: T) => number, list: T[]): T[]```
It returns copy of `list` sorted by `sortFn` function, where `sortFn` needs to return only `-1`, `0` or `1`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%0A%20%20%7Ba%3A%202%7D%2C%0A%20%20%7Ba%3A%203%7D%2C%0A%20%20%7Ba%3A%201%7D%0A%5D%0Aconst%20sortFn%20%3D%20(x%2C%20y)%20%3D%3E%20%7B%0A%20%20return%20x.a%20%3E%20y.a%20%3F%201%20%3A%20-1%0A%7D%0A%0Aconst%20result%20%3D%20R.sort(sortFn%2C%20list)%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A%201%7D%2C%0A%20%20%7Ba%3A%202%7D%2C%0A%20%20%7Ba%3A%203%7D%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.sort</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptsort<T>(sortFn: (a: T, b: T) => number, list: T[]): T[];sort<T>(sortFn: (a: T, b: T) => number): (list: T[]) => T[];```
</details><details><summary><strong>R.sort</strong> source</summary>```javascriptimport { cloneList } from './_internals/cloneList.js'
export function sort(sortFn, list){ if (arguments.length === 1) return _list => sort(sortFn, _list) return cloneList(list).sort(sortFn)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { sort } from './sort.js'
const fn = (a, b) => a > b ? 1 : -1
test('sort', () => { expect(sort((a, b) => a - b)([ 2, 3, 1 ])).toEqual([ 1, 2, 3 ])})
test('it doesn\'t mutate', () => { const list = [ 'foo', 'bar', 'baz' ] expect(sort(fn, list)).toEqual([ 'bar', 'baz', 'foo' ]) expect(list[ 0 ]).toBe('foo') expect(list[ 1 ]).toBe('bar') expect(list[ 2 ]).toBe('baz')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {sort} from 'rambda'
const list = [3, 0, 5, 2, 1]
function sortFn(a: number, b: number): number { return a > b ? 1 : -1}
describe('R.sort', () => { it('happy', () => { const result = sort(sortFn, list) result // $ExpectType number[] }) it('curried', () => { const result = sort(sortFn)(list) result // $ExpectType number[] })})```
</details>[](#sort)
### sortBy
```typescript
sortBy<T>(sortFn: (a: T) => Ord, list: T[]): T[]```
It returns copy of `list` sorted by `sortFn` function, where `sortFn` function returns a value to compare, i.e. it doesn't need to return only `-1`, `0` or `1`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%0A%20%20%7Ba%3A%202%7D%2C%0A%20%20%7Ba%3A%203%7D%2C%0A%20%20%7Ba%3A%201%7D%0A%5D%0Aconst%20sortFn%20%3D%20x%20%3D%3E%20x.a%0A%0Aconst%20result%20%3D%20R.sortBy(sortFn%2C%20list)%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A%201%7D%2C%0A%20%20%7Ba%3A%202%7D%2C%0A%20%20%7Ba%3A%203%7D%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.sortBy</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptsortBy<T>(sortFn: (a: T) => Ord, list: T[]): T[];sortBy<T>(sortFn: (a: T) => Ord): (list: T[]) => T[];sortBy(sortFn: (a: any) => Ord): <T>(list: T[]) => T[];```
</details><details><summary><strong>R.sortBy</strong> source</summary>```javascriptimport { cloneList } from './_internals/cloneList.js'
export function sortBy(sortFn, list){ if (arguments.length === 1) return _list => sortBy(sortFn, _list) const clone = cloneList(list) return clone.sort((a, b) => { const aSortResult = sortFn(a) const bSortResult = sortFn(b) if (aSortResult === bSortResult) return 0 return aSortResult < bSortResult ? -1 : 1 })}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { compose } from './compose.js'import { prop } from './prop.js'import { sortBy } from './sortBy.js'import { toLower } from './toLower.js'
test('happy', () => { const input = [ { a : 2 }, { a : 1 }, { a : 1 }, { a : 3 } ] const expected = [ { a : 1 }, { a : 1 }, { a : 2 }, { a : 3 } ] const result = sortBy(x => x.a)(input) expect(result).toEqual(expected)})
test('with compose', () => { const alice = { name : 'ALICE', age : 101, } const bob = { name : 'Bob', age : -10, } const clara = { name : 'clara', age : 314.159, } const people = [ clara, bob, alice ] const sortByNameCaseInsensitive = sortBy(compose(toLower, prop('name'))) expect(sortByNameCaseInsensitive(people)).toEqual([ alice, bob, clara ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {sortBy, pipe} from 'rambda'
interface Input { a: number,}
describe('R.sortBy', () => { it('passing type to sort function', () => { function fn(x: any): number { return x.a } function fn2(x: Input): number { return x.a } const input = [{a: 2}, {a: 1}, {a: 0}] const result = sortBy(fn, input) const curriedResult = sortBy(fn2)(input) result // $ExpectType { a: number; }[] curriedResult // $ExpectType Input[] result[0].a // $ExpectType number curriedResult[0].a // $ExpectType number }) it('passing type to sort function and list', () => { function fn(x: Input): number { return x.a } const input: Input[] = [{a: 2}, {a: 1}, {a: 0}] const result = sortBy(fn, input) const curriedResult = sortBy(fn)(input) result // $ExpectType Input[] curriedResult // $ExpectType Input[] result[0].a // $ExpectType number }) it('with R.pipe', () => { interface Obj { value: number, } const fn = pipe(sortBy<Obj>(x => x.value)) const result = fn([{value: 1}, {value: 2}]) result // $ExpectType Obj[] })})```
</details>[](#sortBy)
### sortWith
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.sortWith(%5B%0A%20%20%20%20(a%2C%20b)%20%3D%3E%20a.a%20%3D%3D%3D%20b.a%20%3F%200%20%3A%20a.a%20%3E%20b.a%20%3F%201%20%3A%20-1%2C%0A%20%20%20%20(a%2C%20b)%20%3D%3E%20a.b%20%3D%3D%3D%20b.b%20%3F%200%20%3A%20a.b%20%3E%20b.b%20%3F%201%20%3A%20-1%2C%0A%5D%2C%20%5B%0A%20%20%7Ba%3A%201%2C%20b%3A%202%7D%2C%0A%20%20%7Ba%3A%202%2C%20b%3A%201%7D%2C%0A%20%20%7Ba%3A%202%2C%20b%3A%202%7D%2C%0A%20%20%7Ba%3A%201%2C%20b%3A%201%7D%2C%0A%5D)%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Ba%3A%201%2C%20b%3A%201%7D%2C%0A%20%20%7Ba%3A%201%2C%20b%3A%202%7D%2C%0A%20%20%7Ba%3A%202%2C%20b%3A%201%7D%2C%0A%20%20%7Ba%3A%202%2C%20b%3A%202%7D%2C%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.sortWith</strong> example in Rambda REPL</a>[](#sortWith)
### split
```typescript
split(separator: string | RegExp): (str: string) => string[]```
Curried version of `String.prototype.split`
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20str%20%3D%20'foo%7Cbar%7Cbaz'%0Aconst%20separator%20%3D%20'%7C'%0Aconst%20result%20%3D%20R.split(separator%2C%20str)%0A%2F%2F%20%3D%3E%20%5B%20'foo'%2C%20'bar'%2C%20'baz'%20%5D">Try this <strong>R.split</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptsplit(separator: string | RegExp): (str: string) => string[];split(separator: string | RegExp, str: string): string[];```
</details><details><summary><strong>R.split</strong> source</summary>```javascriptexport function split(separator, str){ if (arguments.length === 1) return _str => split(separator, _str) return str.split(separator)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { split } from './split.js'
const str = 'foo|bar|baz'const splitChar = '|'const expected = [ 'foo', 'bar', 'baz' ]
test('happy', () => { expect(split(splitChar, str)).toEqual(expected)})
test('curried', () => { expect(split(splitChar)(str)).toEqual(expected)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {split} from 'rambda'
const str = 'foo|bar|baz'const splitChar = '|'
describe('R.split', () => { it('happy', () => { const result = split(splitChar, str) result // $ExpectType string[] }) it('curried', () => { const result = split(splitChar)(str) result // $ExpectType string[] })})```
</details>[](#split)
### splitAt
```typescript
splitAt<T>(index: number, input: T[]): [T[], T[]]```
It splits string or array at a given index.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%201%2C%202%2C%203%20%5D%0Aconst%20result%20%3D%20R.splitAt(2%2C%20list)%0A%2F%2F%20%3D%3E%20%5B%5B%201%2C%202%20%5D%2C%20%5B%203%20%5D%5D">Try this <strong>R.splitAt</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptsplitAt<T>(index: number, input: T[]): [T[], T[]];splitAt(index: number, input: string): [string, string];splitAt(index: number): { <T>(input: T[]): [T[], T[]]; (input: string): [string, string];};```
</details><details><summary><strong>R.splitAt</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'import { drop } from './drop.js'import { maybe } from './maybe.js'import { take } from './take.js'
export function splitAt(index, input){ if (arguments.length === 1){ return _list => splitAt(index, _list) } if (!input) throw new TypeError(`Cannot read property 'slice' of ${ input }`) if (!isArray(input) && typeof input !== 'string') return [ [], [] ] const correctIndex = maybe( index < 0, input.length + index < 0 ? 0 : input.length + index, index ) return [ take(correctIndex, input), drop(correctIndex, input) ]}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { splitAt as splitAtRamda } from 'ramda'
import { splitAt } from './splitAt.js'
const list = [ 1, 2, 3 ]const str = 'foo bar'
test('with array', () => { const result = splitAt(2, list) expect(result).toEqual([ [ 1, 2 ], [ 3 ] ])})
test('with array - index is negative number', () => { const result = splitAt(-6, list) expect(result).toEqual([ [], list ])})
test('with array - index is out of scope', () => { const result = splitAt(4, list) expect(result).toEqual([ [ 1, 2, 3 ], [] ])})
test('with string', () => { const result = splitAt(4, str) expect(result).toEqual([ 'foo ', 'bar' ])})
test('with string - index is negative number', () => { const result = splitAt(-2, str) expect(result).toEqual([ 'foo b', 'ar' ])})
test('with string - index is out of scope', () => { const result = splitAt(10, str) expect(result).toEqual([ str, '' ])})
test('with array - index is out of scope', () => { const result = splitAt(4)(list) expect(result).toEqual([ [ 1, 2, 3 ], [] ])})
const badInputs = [ 1, true, /foo/g, {} ]const throwingBadInputs = [ null, undefined ]
test('with bad inputs', () => { throwingBadInputs.forEach(badInput => { expect(() => splitAt(1, badInput)).toThrowWithMessage(TypeError, `Cannot read property 'slice' of ${ badInput }`) expect(() => splitAtRamda(1, badInput)).toThrowWithMessage(TypeError, `Cannot read properties of ${ badInput } (reading 'slice')`) }) badInputs.forEach(badInput => { const result = splitAt(1, badInput) const ramdaResult = splitAtRamda(1, badInput) expect(result).toEqual(ramdaResult) })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {splitAt} from 'rambda'
const index = 1const str = 'foo'const list = [1, 2, 3]
describe('R.splitAt with array', () => { it('happy', () => { const result = splitAt(index, list) result // $ExpectType [number[], number[]] }) it('curried', () => { const result = splitAt(index)(list) result // $ExpectType [number[], number[]] })})
describe('R.splitAt with string', () => { it('happy', () => { const result = splitAt(index, str) result // $ExpectType [string, string] }) it('curried', () => { const result = splitAt(index)(str) result // $ExpectType [string, string] })})```
</details>[](#splitAt)
### splitEvery
```typescript
splitEvery<T>(sliceLength: number, input: T[]): (T[])[]```
It splits `input` into slices of `sliceLength`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.splitEvery(2%2C%20%5B1%2C%202%2C%203%5D)%2C%20%0A%20%20R.splitEvery(3%2C%20'foobar')%20%0A%5D%0A%0Aconst%20expected%20%3D%20%5B%0A%20%20%5B%5B1%2C%202%5D%2C%20%5B3%5D%5D%2C%0A%20%20%5B'foo'%2C%20'bar'%5D%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.splitEvery</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptsplitEvery<T>(sliceLength: number, input: T[]): (T[])[];splitEvery(sliceLength: number, input: string): string[];splitEvery(sliceLength: number): { (input: string): string[]; <T>(input: T[]): (T[])[];};```
</details><details><summary><strong>R.splitEvery</strong> source</summary>```javascriptexport function splitEvery(sliceLength, listOrString){ if (arguments.length === 1){ return _listOrString => splitEvery(sliceLength, _listOrString) } if (sliceLength < 1){ throw new Error('First argument to splitEvery must be a positive integer') } const willReturn = [] let counter = 0 while (counter < listOrString.length){ willReturn.push(listOrString.slice(counter, counter += sliceLength)) } return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { splitEvery } from './splitEvery.js'
test('happy', () => { expect(splitEvery(3, [ 1, 2, 3, 4, 5, 6, 7 ])).toEqual([ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7 ], ]) expect(splitEvery(3)('foobarbaz')).toEqual([ 'foo', 'bar', 'baz' ])})
test('with bad input', () => { expect(() => expect(splitEvery(0)('foo')).toEqual([ 'f', 'o', 'o' ])).toThrowErrorMatchingInlineSnapshot('"First argument to splitEvery must be a positive integer"')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {splitEvery} from 'rambda'
const list = [1, 2, 3, 4, 5, 6, 7]
describe('R.splitEvery', () => { it('happy', () => { const result = splitEvery(3, list) result // $ExpectType number[][] }) it('curried', () => { const result = splitEvery(3)(list) result // $ExpectType number[][] })})```
</details>[](#splitEvery)
### splitWhen
```typescript
splitWhen<T, U>(predicate: Predicate<T>, list: U[]): (U[])[]```
It splits `list` to two arrays according to a `predicate` function.
The first array contains all members of `list` before `predicate` returns `true`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%201%2C%202%5D%0Aconst%20result%20%3D%20R.splitWhen(R.equals(2)%2C%20list)%0A%2F%2F%20%3D%3E%20%5B%5B1%5D%2C%20%5B2%2C%201%2C%202%5D%5D">Try this <strong>R.splitWhen</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptsplitWhen<T, U>(predicate: Predicate<T>, list: U[]): (U[])[];splitWhen<T>(predicate: Predicate<T>): <U>(list: U[]) => (U[])[];```
</details><details><summary><strong>R.splitWhen</strong> source</summary>```javascriptexport function splitWhen(predicate, input){ if (arguments.length === 1){ return _input => splitWhen(predicate, _input) } if (!input) throw new TypeError(`Cannot read property 'length' of ${ input }`) const preFound = [] const postFound = [] let found = false let counter = -1 while (counter++ < input.length - 1){ if (found){ postFound.push(input[ counter ]) } else if (predicate(input[ counter ])){ postFound.push(input[ counter ]) found = true } else { preFound.push(input[ counter ]) } } return [ preFound, postFound ]}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { splitWhen as splitWhenRamda } from 'ramda'
import { equals } from './equals.js'import { splitWhen } from './splitWhen.js'
const list = [ 1, 2, 1, 2 ]
test('happy', () => { const result = splitWhen(equals(2), list) expect(result).toEqual([ [ 1 ], [ 2, 1, 2 ] ])})
test('when predicate returns false', () => { const result = splitWhen(equals(3))(list) expect(result).toEqual([ list, [] ])})
const badInputs = [ 1, true, /foo/g, {} ]const throwingBadInputs = [ null, undefined ]
test('with bad inputs', () => { throwingBadInputs.forEach(badInput => { expect(() => splitWhen(equals(2), badInput)).toThrowWithMessage(TypeError, `Cannot read property 'length' of ${ badInput }`) expect(() => splitWhenRamda(equals(2), badInput)).toThrowWithMessage(TypeError, `Cannot read properties of ${ badInput } (reading 'length')`) }) badInputs.forEach(badInput => { const result = splitWhen(equals(2), badInput) const ramdaResult = splitWhenRamda(equals(2), badInput) expect(result).toEqual(ramdaResult) })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {splitWhen} from 'rambda'
const list = [1, 2, 1, 2]const predicate = (x: number) => x === 2
describe('R.splitWhen', () => { it('happy', () => { const result = splitWhen(predicate, list) result // $ExpectType number[][] }) it('curried', () => { const result = splitWhen(predicate)(list) result // $ExpectType number[][] })})```
</details>[](#splitWhen)
### startsWith
```typescript
startsWith<T extends string>(question: T, input: string): boolean```
When iterable is a string, then it behaves as `String.prototype.startsWith`.When iterable is a list, then it uses R.equals to determine if the target list starts in the same way as the given target.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20str%20%3D%20'foo-bar'%0Aconst%20list%20%3D%20%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%2C%20%7Ba%3A3%7D%5D%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.startsWith('foo'%2C%20str)%2C%0A%20%20R.startsWith(%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%5D%2C%20list)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20true%5D">Try this <strong>R.startsWith</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptstartsWith<T extends string>(question: T, input: string): boolean;startsWith<T extends string>(question: T): (input: string) => boolean;startsWith<T>(question: T[], input: T[]): boolean;startsWith<T>(question: T[]): (input: T[]) => boolean;```
</details><details><summary><strong>R.startsWith</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'import { equals } from './equals.js'
export function startsWith(question, iterable){ if (arguments.length === 1) return _iterable => startsWith(question, _iterable) if (typeof iterable === 'string'){ return iterable.startsWith(question) } if (!isArray(question)) return false let correct = true const filtered = question.filter((x, index) => { if (!correct) return false const result = equals(x, iterable[ index ]) if (!result) correct = false return result }) return filtered.length === question.length}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { startsWith as startsWithRamda } from 'ramda'
import { compareCombinations } from './_internals/testUtils.js'import { possibleIterables, possibleTargets } from './endsWith.spec.js'import { startsWith } from './startsWith.js'
test('with string', () => { expect(startsWith('foo', 'foo-bar')).toBeTrue() expect(startsWith('baz')('foo-bar')).toBeFalse()})
test('use R.equals with array', () => { const list = [ { a : 1 }, { a : 2 }, { a : 3 } ] expect(startsWith({ a : 1 }, list)).toBeFalse() expect(startsWith([ { a : 1 } ], list)).toBeTrue() expect(startsWith([ { a : 1 }, { a : 2 } ], list)).toBeTrue() expect(startsWith(list, list)).toBeTrue() expect(startsWith([ { a : 2 } ], list)).toBeFalse()})
describe('brute force', () => { compareCombinations({ fn : startsWith, fnRamda : startsWithRamda, firstInput : possibleTargets, secondInput : possibleIterables, callback : errorsCounters => { expect(errorsCounters).toMatchInlineSnapshot(` { "ERRORS_MESSAGE_MISMATCH": 0, "ERRORS_TYPE_MISMATCH": 0, "RESULTS_MISMATCH": 0, "SHOULD_NOT_THROW": 0, "SHOULD_THROW": 0, "TOTAL_TESTS": 32, } `) }, })})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {startsWith} from 'rambda'
describe('R.startsWith - array', () => { const question = [{a: 1}] const iterable = [{a: 1}, {a: 2}] it('happy', () => { const result = startsWith(question, iterable) result // $ExpectType boolean }) it('curried', () => { const result = startsWith(question)(iterable) result // $ExpectType boolean })})
describe('R.startsWith - string', () => { const question = 'foo' const iterable = 'foo bar' it('happy', () => { const result = startsWith(question, iterable) result // $ExpectType boolean }) it('curried', () => { const result = startsWith(question)(iterable) result // $ExpectType boolean })})```
</details>[](#startsWith)
### subtract
Curried version of `x - y`
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20x%20%3D%203%0Aconst%20y%20%3D%201%0A%0Aconst%20result%20%3D%20R.subtract(x%2C%20y)%20%0A%2F%2F%20%3D%3E%202">Try this <strong>R.subtract</strong> example in Rambda REPL</a>[](#subtract)
### sum
```typescript
sum(list: number[]): number```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.sum(%5B1%2C%202%2C%203%2C%204%2C%205%5D)%20%0A%2F%2F%20%3D%3E%2015">Try this <strong>R.sum</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptsum(list: number[]): number;```
</details><details><summary><strong>R.sum</strong> source</summary>```javascriptexport function sum(list){ return list.reduce((prev, current) => prev + current, 0)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { sum } from './sum.js'
test('happy', () => { expect(sum([ 1, 2, 3, 4, 5 ])).toBe(15)})```
</details>[](#sum)
### swap
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.swap(1%2C%202%2C%20%5B1%2C%202%2C%203%5D)%0A%2F%2F%20%3D%3E%20%5B1%2C%203%2C%202%5D">Try this <strong>R.swap</strong> example in Rambda REPL</a>[](#swap)
### symmetricDifference
```typescript
symmetricDifference<T>(x: T[], y: T[]): T[]```
It returns a merged list of `x` and `y` with all equal elements removed.
`R.equals` is used to determine equality.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20x%20%3D%20%5B%201%2C%202%2C%203%2C%204%20%5D%0Aconst%20y%20%3D%20%5B%203%2C%204%2C%205%2C%206%20%5D%0A%0Aconst%20result%20%3D%20R.symmetricDifference(x%2C%20y)%0A%2F%2F%20%3D%3E%20%5B%201%2C%202%2C%205%2C%206%20%5D">Try this <strong>R.symmetricDifference</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptsymmetricDifference<T>(x: T[], y: T[]): T[];symmetricDifference<T>(x: T[]): <T>(y: T[]) => T[];```
</details><details><summary><strong>R.symmetricDifference</strong> source</summary>```javascriptimport { concat } from './concat.js'import { filter } from './filter.js'import { includes } from './includes.js'
export function symmetricDifference(x, y){ if (arguments.length === 1){ return _y => symmetricDifference(x, _y) } return concat(filter(value => !includes(value, y), x), filter(value => !includes(value, x), y))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { symmetricDifference } from './symmetricDifference.js'
test('symmetricDifference', () => { const list1 = [ 1, 2, 3, 4 ] const list2 = [ 3, 4, 5, 6 ] expect(symmetricDifference(list1)(list2)).toEqual([ 1, 2, 5, 6 ]) expect(symmetricDifference([], [])).toEqual([])})
test('symmetricDifference with objects', () => { const list1 = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ] const list2 = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ] expect(symmetricDifference(list1)(list2)).toEqual([ { id : 1 }, { id : 2 }, { id : 5 }, { id : 6 }, ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {symmetricDifference} from 'rambda'
describe('R.symmetricDifference', () => { it('happy', () => { const list1 = [1, 2, 3, 4] const list2 = [3, 4, 5, 6] const result = symmetricDifference(list1, list2) result // $ExpectType number[] }) it('curried', () => { const list1 = [{id: 1}, {id: 2}, {id: 3}, {id: 4}] const list2 = [{id: 3}, {id: 4}, {id: 5}, {id: 6}] const result = symmetricDifference(list1)(list2) result // $ExpectType { id: number; }[] })})```
</details>[](#symmetricDifference)
### T
```typescript
T(): boolean```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.T()%20%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.T</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptT(): boolean;```
</details><details><summary><strong>R.T</strong> source</summary>```javascriptexport function T(){ return true}```
</details>[](#T)
### tail
```typescript
tail<T extends unknown[]>(input: T): T extends [any, ...infer U] ? U : [...T]```
It returns all but the first element of `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20R.tail(%5B1%2C%202%2C%203%5D)%2C%20%20%0A%20%20R.tail('foo')%20%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B2%2C%203%5D%2C%20'oo'%5D">Try this <strong>R.tail</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttail<T extends unknown[]>(input: T): T extends [any, ...infer U] ? U : [...T];tail(input: string): string;```
</details><details><summary><strong>R.tail</strong> source</summary>```javascriptimport { drop } from './drop.js'
export function tail(listOrString){ return drop(1, listOrString)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { tail } from './tail.js'
test('tail', () => { expect(tail([ 1, 2, 3 ])).toEqual([ 2, 3 ]) expect(tail([ 1, 2 ])).toEqual([ 2 ]) expect(tail([ 1 ])).toEqual([]) expect(tail([])).toEqual([]) expect(tail('abc')).toBe('bc') expect(tail('ab')).toBe('b') expect(tail('a')).toBe('') expect(tail('')).toBe('')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {tail} from 'rambda'
describe('R.tail', () => { it('with string', () => { const result = tail('foo') result // $ExpectType string }) it('with list - one type', () => { const result = tail([1, 2, 3]) result // $ExpectType number[] }) it('with list - mixed types', () => { const result = tail(['foo', 'bar', 1, 2, 3]) result // $ExpectType (string | number)[] })})```
</details>[](#tail)
### take
```typescript
take<T>(howMany: number, input: T[]): T[]```
It returns the first `howMany` elements of `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20howMany%20%3D%202%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.take(howMany%2C%20%5B1%2C%202%2C%203%5D)%2C%0A%20%20R.take(howMany%2C%20'foobar')%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B1%2C%202%5D%2C%20'fo'%5D">Try this <strong>R.take</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttake<T>(howMany: number, input: T[]): T[];take(howMany: number, input: string): string;take<T>(howMany: number): { <T>(input: T[]): T[]; (input: string): string;};```
</details><details><summary><strong>R.take</strong> source</summary>```javascriptimport baseSlice from './_internals/baseSlice.js'
export function take(howMany, listOrString){ if (arguments.length === 1) return _listOrString => take(howMany, _listOrString) if (howMany < 0) return listOrString.slice() if (typeof listOrString === 'string') return listOrString.slice(0, howMany) return baseSlice( listOrString, 0, howMany )}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { take } from './take.js'
test('happy', () => { const arr = [ 'foo', 'bar', 'baz' ] expect(take(1, arr)).toEqual([ 'foo' ]) expect(arr).toEqual([ 'foo', 'bar', 'baz' ]) expect(take(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar' ]) expect(take(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ]) expect(take(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ]) expect(take(3)('rambda')).toBe('ram')})
test('with negative index', () => { expect(take(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ]) expect(take(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])})
test('with zero index', () => { expect(take(0, [ 1, 2, 3 ])).toEqual([])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {take} from 'rambda'
const list = [1, 2, 3, 4]const str = 'foobar'const howMany = 2
describe('R.take - array', () => { it('happy', () => { const result = take(howMany, list) result // $ExpectType number[] }) it('curried', () => { const result = take(howMany)(list) result // $ExpectType number[] })})
describe('R.take - string', () => { it('happy', () => { const result = take(howMany, str) result // $ExpectType string }) it('curried', () => { const result = take(howMany)(str) result // $ExpectType string })})```
</details>[](#take)
### takeLast
```typescript
takeLast<T>(howMany: number, input: T[]): T[]```
It returns the last `howMany` elements of `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20howMany%20%3D%202%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.takeLast(howMany%2C%20%5B1%2C%202%2C%203%5D)%2C%0A%20%20R.takeLast(howMany%2C%20'foobar')%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5B%5B2%2C%203%5D%2C%20'ar'%5D">Try this <strong>R.takeLast</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttakeLast<T>(howMany: number, input: T[]): T[];takeLast(howMany: number, input: string): string;takeLast<T>(howMany: number): { <T>(input: T[]): T[]; (input: string): string;};```
</details><details><summary><strong>R.takeLast</strong> source</summary>```javascriptimport baseSlice from './_internals/baseSlice.js'
export function takeLast(howMany, listOrString){ if (arguments.length === 1) return _listOrString => takeLast(howMany, _listOrString) const len = listOrString.length if (howMany < 0) return listOrString.slice() let numValue = howMany > len ? len : howMany if (typeof listOrString === 'string') return listOrString.slice(len - numValue) numValue = len - numValue return baseSlice( listOrString, numValue, len )}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { takeLast } from './takeLast.js'
test('with arrays', () => { expect(takeLast(1, [ 'foo', 'bar', 'baz' ])).toEqual([ 'baz' ]) expect(takeLast(2)([ 'foo', 'bar', 'baz' ])).toEqual([ 'bar', 'baz' ]) expect(takeLast(3, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ]) expect(takeLast(4, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ]) expect(takeLast(10, [ 'foo', 'bar', 'baz' ])).toEqual([ 'foo', 'bar', 'baz' ])})
test('with strings', () => { expect(takeLast(3, 'rambda')).toBe('bda') expect(takeLast(7, 'rambda')).toBe('rambda')})
test('with negative index', () => { expect(takeLast(-1, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ]) expect(takeLast(-Infinity, [ 1, 2, 3 ])).toEqual([ 1, 2, 3 ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {takeLast} from 'rambda'
const list = [1, 2, 3, 4]const str = 'foobar'const howMany = 2
describe('R.takeLast - array', () => { it('happy', () => { const result = takeLast(howMany, list) result // $ExpectType number[] }) it('curried', () => { const result = takeLast(howMany)(list) result // $ExpectType number[] })})
describe('R.takeLast - string', () => { it('happy', () => { const result = takeLast(howMany, str) result // $ExpectType string }) it('curried', () => { const result = takeLast(howMany)(str) result // $ExpectType string })})```
</details>[](#takeLast)
### takeLastWhile
```typescript
takeLastWhile(predicate: (x: string) => boolean, input: string): string```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.takeLastWhile(%0A%20%20x%20%3D%3E%20x%20%3E%202%2C%0A%20%20%5B1%2C%202%2C%203%2C%204%5D%0A)%0A%2F%2F%20%3D%3E%20%5B3%2C%204%5D">Try this <strong>R.takeLastWhile</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttakeLastWhile(predicate: (x: string) => boolean, input: string): string;takeLastWhile(predicate: (x: string) => boolean): (input: string) => string;takeLastWhile<T>(predicate: (x: T) => boolean, input: T[]): T[];takeLastWhile<T>(predicate: (x: T) => boolean): <T>(input: T[]) => T[];```
</details><details><summary><strong>R.takeLastWhile</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'
export function takeLastWhile(predicate, input){ if (arguments.length === 1){ return _input => takeLastWhile(predicate, _input) } if (input.length === 0) return input const toReturn = [] let counter = input.length while (counter){ const item = input[ --counter ] if (!predicate(item)){ break } toReturn.push(item) } return isArray(input) ? toReturn.reverse() : toReturn.reverse().join('')}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { takeLastWhile } from './takeLastWhile.js'const assert = require('assert')
const list = [ 1, 2, 3, 4 ]
test('happy', () => { const predicate = x => x > 2 const result = takeLastWhile(predicate, list) expect(result).toEqual([ 3, 4 ])})
test('predicate is always true', () => { const predicate = () => true const result = takeLastWhile(predicate)(list) expect(result).toEqual(list)})
test('predicate is always false', () => { const predicate = () => false const result = takeLastWhile(predicate, list) expect(result).toEqual([])})
test('with string', () => { const result = takeLastWhile(x => x !== 'F', 'FOOBAR') expect(result).toBe('OOBAR')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {takeLastWhile} from 'rambda'
const list = [1, 2, 3]const str = 'FOO'
describe('R.takeLastWhile', () => { it('with array', () => { const result = takeLastWhile(x => x > 1, list) result // $ExpectType number[] }) it('with array - curried', () => { const result = takeLastWhile(x => x > 1, list) result // $ExpectType number[] }) it('with string', () => { const result = takeLastWhile(x => x !== 'F', str) result // $ExpectType string }) it('with string - curried', () => { const result = takeLastWhile(x => x !== 'F')(str) result // $ExpectType string })})```
</details>[](#takeLastWhile)
### takeWhile
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20predicate%20%3D%20x%20%3D%3E%20x%20%3C%203%0A%0Aconst%20result%20%3D%20R.takeWhile(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.takeWhile</strong> example in Rambda REPL</a>[](#takeWhile)
### tap
```typescript
tap<T>(fn: (x: T) => void, input: T): T```
It applies function `fn` to input `x` and returns `x`.
One use case is debugging in the middle of `R.compose`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%202%2C%203%5D%0A%0AR.compose(%0A%20%20R.map(x%20%3D%3E%20x%20*%202)%0A%20%20R.tap(console.log)%2C%0A%20%20R.filter(x%20%3D%3E%20x%20%3E%201)%0A)(list)%0A%2F%2F%20%3D%3E%20%602%60%20and%20%603%60%20will%20be%20logged">Try this <strong>R.tap</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttap<T>(fn: (x: T) => void, input: T): T;tap<T>(fn: (x: T) => void): (input: T) => T;```
</details><details><summary><strong>R.tap</strong> source</summary>```javascriptexport function tap(fn, x){ if (arguments.length === 1) return _x => tap(fn, _x) fn(x) return x}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { tap } from './tap.js'
test('tap', () => { let a = 1 const sayX = x => a = x expect(tap(sayX, 100)).toBe(100) expect(tap(sayX)(100)).toBe(100) expect(a).toBe(100)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {tap, pipe} from 'rambda'
describe('R.tap', () => { it('happy', () => { pipe( tap(x => { x // $ExpectType number[] }), (x: number[]) => x.length )([1, 2]) })})```
</details>[](#tap)
### test
```typescript
test(regExpression: RegExp): (str: string) => boolean```
It determines whether `str` matches `regExpression`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.test(%2F%5Ef%2F%2C%20'foo')%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.test</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttest(regExpression: RegExp): (str: string) => boolean;test(regExpression: RegExp, str: string): boolean;```
</details><details><summary><strong>R.test</strong> source</summary>```javascriptexport function test(pattern, str){ if (arguments.length === 1) return _str => test(pattern, _str) if (typeof pattern === 'string'){ throw new TypeError(`R.test requires a value of type RegExp as its first argument; received "${ pattern }"`) } return str.search(pattern) !== -1}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { test as testMethod } from './test.js'
test('happy', () => { expect(testMethod(/^x/, 'xyz')).toBeTrue() expect(testMethod(/^y/)('xyz')).toBeFalse()})
test('throws if first argument is not regex', () => { expect(() => testMethod('foo', 'bar')).toThrowErrorMatchingInlineSnapshot('"R.test requires a value of type RegExp as its first argument; received "foo""')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {test} from 'rambda'
const input = 'foo 'const regex = /foo/
describe('R.test', () => { it('happy', () => { const result = test(regex, input) result // $ExpectType boolean }) it('curried', () => { const result = test(regex)(input) result // $ExpectType boolean })})```
</details>[](#test)
### times
```typescript
times<T>(fn: (i: number) => T, howMany: number): T[]```
It returns the result of applying function `fn` over members of range array.
The range array includes numbers between `0` and `howMany`(exclusive).
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20x%20%3D%3E%20x%20*%202%0Aconst%20howMany%20%3D%205%0A%0Aconst%20result%20%3D%20R.times(fn%2C%20howMany)%0A%2F%2F%20%3D%3E%20%5B0%2C%202%2C%204%2C%206%2C%208%5D">Try this <strong>R.times</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttimes<T>(fn: (i: number) => T, howMany: number): T[];times<T>(fn: (i: number) => T): (howMany: number) => T[];```
</details><details><summary><strong>R.times</strong> source</summary>```javascriptimport { isInteger } from './_internals/isInteger.js'import { map } from './map.js'import { range } from './range.js'
export function times(fn, howMany){ if (arguments.length === 1) return _howMany => times(fn, _howMany) if (!isInteger(howMany) || howMany < 0){ throw new RangeError('n must be an integer') } return map(fn, range(0, howMany))}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport assert from 'assert'
import { identity } from './identity.js'import { times } from './times.js'
test('happy', () => { const result = times(identity, 5) expect(result).toEqual([ 0, 1, 2, 3, 4 ])})
test('with bad input', () => { assert.throws(() => { times(3)('cheers!') }, RangeError) assert.throws(() => { times(identity, -1) }, RangeError)})
test('curry', () => { const result = times(identity)(5) expect(result).toEqual([ 0, 1, 2, 3, 4 ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {times, identity} from 'rambda'
describe('R.times', () => { it('happy', () => { const result = times(identity, 5) result // $ExpectType number[] })})```
</details>[](#times)
### toLower
```typescript
toLower<S extends string>(str: S): Lowercase<S>```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.toLower('FOO')%0A%2F%2F%20%3D%3E%20'foo'">Try this <strong>R.toLower</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttoLower<S extends string>(str: S): Lowercase<S>;toLower(str: string): string;```
</details><details><summary><strong>R.toLower</strong> source</summary>```javascriptexport function toLower(str){ return str.toLowerCase()}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { toLower } from './toLower.js'
test('toLower', () => { expect(toLower('FOO|BAR|BAZ')).toBe('foo|bar|baz')})```
</details>[](#toLower)
### toPairs
```typescript
toPairs<O extends object, K extends Extract<keyof O, string | number>>(obj: O): Array<{ [key in K]: [`${key}`, O[key]] }[K]>```
It transforms an object to a list.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%7B%0A%20%20a%20%3A%201%2C%0A%20%20b%20%3A%202%2C%0A%20%20c%20%3A%20%5B%203%2C%204%20%5D%2C%0A%7D%0Aconst%20expected%20%3D%20%5B%20%5B%20'a'%2C%201%20%5D%2C%20%5B%20'b'%2C%202%20%5D%2C%20%5B%20'c'%2C%20%5B%203%2C%204%20%5D%20%5D%20%5D%0A%0Aconst%20result%20%3D%20R.toPairs(list)%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.toPairs</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttoPairs<O extends object, K extends Extract<keyof O, string | number>>(obj: O): Array<{ [key in K]: [`${key}`, O[key]] }[K]>;toPairs<S>(obj: Record<string | number, S>): Array<[string, S]>;```
</details><details><summary><strong>R.toPairs</strong> source</summary>```javascriptexport function toPairs(obj){ return Object.entries(obj)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { toPairs } from './toPairs.js'
const obj = { a : 1, b : 2, c : [ 3, 4 ],}const expected = [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', [ 3, 4 ] ],]
test('happy', () => { expect(toPairs(obj)).toEqual(expected)})```
</details>[](#toPairs)
### toString
```typescript
toString(x: unknown): string```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.toString(%5B1%2C%202%5D)%20%0A%2F%2F%20%3D%3E%20'1%2C2'">Try this <strong>R.toString</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttoString(x: unknown): string;```
</details><details><summary><strong>R.toString</strong> source</summary>```javascriptexport function toString(x){ return x.toString()}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { toString } from './toString.js'
test('happy', () => { expect(toString([ 1, 2, 3 ])).toBe('1,2,3')})```
</details>[](#toString)
### toUpper
```typescript
toUpper<S extends string>(str: S): Uppercase<S>```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.toUpper('foo')%0A%2F%2F%20%3D%3E%20'FOO'">Try this <strong>R.toUpper</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttoUpper<S extends string>(str: S): Uppercase<S>;toUpper(str: string): string;```
</details><details><summary><strong>R.toUpper</strong> source</summary>```javascriptexport function toUpper(str){ return str.toUpperCase()}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { toUpper } from './toUpper.js'
test('toUpper', () => { expect(toUpper('foo|bar|baz')).toBe('FOO|BAR|BAZ')})```
</details>[](#toUpper)
### transpose
```typescript
transpose<T>(list: (T[])[]): (T[])[]```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%5B10%2C%2011%5D%2C%20%5B20%5D%2C%20%5B%5D%2C%20%5B30%2C%2031%2C%2032%5D%5D%0Aconst%20expected%20%3D%20%5B%5B10%2C%2020%2C%2030%5D%2C%20%5B11%2C%2031%5D%2C%20%5B32%5D%5D%0A%0Aconst%20result%20%3D%20R.transpose(list)%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.transpose</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttranspose<T>(list: (T[])[]): (T[])[];```
</details><details><summary><strong>R.transpose</strong> source</summary>```javascriptimport { isArray } from './_internals/isArray.js'
export function transpose(array){ return array.reduce((acc, el) => { el.forEach((nestedEl, i) => isArray(acc[ i ]) ? acc[ i ].push(nestedEl) : acc.push([ nestedEl ])) return acc }, [])}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { transpose } from './transpose.js'
test('happy', () => { const input = [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', 3 ], ] expect(transpose(input)).toEqual([ [ 'a', 'b', 'c' ], [ 1, 2, 3 ], ])})
test('when rows are shorter', () => { const actual = transpose([ [ 10, 11 ], [ 20 ], [], [ 30, 31, 32 ] ]) const expected = [ [ 10, 20, 30 ], [ 11, 31 ], [ 32 ] ] expect(actual).toEqual(expected)})
test('with empty array', () => { expect(transpose([])).toEqual([])})
test('array with falsy values', () => { const actual = transpose([ [ true, false, undefined, null ], [ null, undefined, false, true ], ]) const expected = [ [ true, null ], [ false, undefined ], [ undefined, false ], [ null, true ], ] expect(actual).toEqual(expected)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {transpose} from 'rambda'
const input = [ ['a', 1], ['b', 2], ['c', 3],]
describe('R.transpose', () => { it('happy', () => { const result = transpose(input) result // $ExpectType (string | number)[][] })})```
</details>[](#transpose)
### trim
```typescript
trim(str: string): string```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.trim('%20%20foo%20%20')%20%0A%2F%2F%20%3D%3E%20'foo'">Try this <strong>R.trim</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescripttrim(str: string): string;```
</details><details><summary><strong>R.trim</strong> source</summary>```javascriptexport function trim(str){ return str.trim()}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { trim } from './trim.js'
test('trim', () => { expect(trim(' foo ')).toBe('foo')})```
</details>[](#trim)
### tryCatch
It returns function that runs `fn` in `try/catch` block. If there was an error, then `fallback` is used to return the result. Note that `fn` can be value or asynchronous/synchronous function(unlike `Ramda` where fallback can only be a synchronous function).
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20x%20%3D%3E%20x.foo%0A%0Aconst%20result%20%3D%20%5B%0A%20%20R.tryCatch(fn%2C%20false)(null)%2C%0A%20%20R.tryCatch(fn%2C%20false)(%7Bfoo%3A%20'bar'%7D)%0A%5D%0A%2F%2F%20%3D%3E%20%5Bfalse%2C%20'bar'%5D">Try this <strong>R.tryCatch</strong> example in Rambda REPL</a>[](#tryCatch)
### type
It accepts any input and it returns its type.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.type(()%20%3D%3E%20%7B%7D)%20%2F%2F%20%3D%3E%20'Function'%0AR.type(async%20()%20%3D%3E%20%7B%7D)%20%2F%2F%20%3D%3E%20'Async'%0AR.type(%5B%5D)%20%2F%2F%20%3D%3E%20'Array'%0AR.type(%7B%7D)%20%2F%2F%20%3D%3E%20'Object'%0AR.type('foo')%20%2F%2F%20%3D%3E%20'String'%0AR.type(1)%20%2F%2F%20%3D%3E%20'Number'%0AR.type(true)%20%2F%2F%20%3D%3E%20'Boolean'%0AR.type(null)%20%2F%2F%20%3D%3E%20'Null'%0AR.type(%2F%5BA-z%5D%2F)%20%2F%2F%20%3D%3E%20'RegExp'%0AR.type('foo'*1)%20%2F%2F%20%3D%3E%20'NaN'%0A%0Aconst%20delay%20%3D%20ms%20%3D%3E%20new%20Promise(resolve%20%3D%3E%20%7B%0A%20%20setTimeout(function%20()%20%7B%0A%20%20%20%20resolve()%0A%20%20%7D%2C%20ms)%0A%7D)%0AR.type(delay)%20%2F%2F%20%3D%3E%20'Promise'">Try this <strong>R.type</strong> example in Rambda REPL</a>[](#type)
### unapply
```typescript
unapply<T = any>(fn: (args: any[]) => T): (...args: any[]) => T```
It calls a function `fn` with the list of values of the returned function.
`R.unapply` is the opposite of `R.apply` method.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.unapply(JSON.stringify)(1%2C%202%2C%203)%0A%2F%2F%3D%3E%20'%5B1%2C2%2C3%5D'">Try this <strong>R.unapply</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptunapply<T = any>(fn: (args: any[]) => T): (...args: any[]) => T;```
</details><details><summary><strong>R.unapply</strong> source</summary>```javascriptexport function unapply(fn){ return function (...args){ return fn.call(this, args) }}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { apply } from './apply.js'import { converge } from './converge.js'import { identity } from './identity.js'import { prop } from './prop.js'import { sum } from './sum.js'import { unapply } from './unapply.js'
test('happy', () => { const fn = unapply(identity) expect(fn( 1, 2, 3 )).toEqual([ 1, 2, 3 ]) expect(fn()).toEqual([])})
test('returns a function which is always passed one argument', () => { const fn = unapply(function (){ return arguments.length }) expect(fn('x')).toBe(1) expect(fn('x', 'y')).toBe(1) expect(fn( 'x', 'y', 'z' )).toBe(1)})
test('forwards arguments to decorated function as an array', () => { const fn = unapply(xs => '[' + xs + ']') expect(fn(2)).toBe('[2]') expect(fn(2, 4)).toBe('[2,4]') expect(fn( 2, 4, 6 )).toBe('[2,4,6]')})
test('returns a function with length 0', () => { const fn = unapply(identity) expect(fn).toHaveLength(0)})
test('is the inverse of R.apply', () => { let a, b, c, d, e, f, g, n const rand = function (){ return Math.floor(200 * Math.random()) - 100 } f = Math.max g = unapply(apply(f)) n = 1 while (n <= 100){ a = rand() b = rand() c = rand() d = rand() e = rand() expect(f( a, b, c, d, e )).toEqual(g( a, b, c, d, e )) n += 1 } f = function (xs){ return '[' + xs + ']' } g = apply(unapply(f)) n = 1 while (n <= 100){ a = rand() b = rand() c = rand() d = rand() e = rand() expect(f([ a, b, c, d, e ])).toEqual(g([ a, b, c, d, e ])) n += 1 }})
test('it works with converge', () => { const fn = unapply(sum) const convergeFn = converge(fn, [ prop('a'), prop('b'), prop('c') ]) const obj = { a : 1337, b : 42, c : 1, } const expected = 1337 + 42 + 1 expect(convergeFn(obj)).toEqual(expected)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {join, unapply, sum} from 'rambda'
describe('R.unapply', () => { it('happy', () => { const fn = unapply(sum) fn(1, 2, 3) // $ExpectType number }) it('joins a string', () => { const fn = unapply(join('')) fn('s', 't', 'r', 'i', 'n', 'g') // $ExpectType string })})```
</details>[](#unapply)
### union
```typescript
union<T>(x: T[], y: T[]): T[]```
It takes two lists and return a new list containing a merger of both list with removed duplicates.
`R.equals` is used to compare for duplication.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.union(%5B1%2C2%2C3%5D%2C%20%5B3%2C4%2C5%5D)%3B%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%203%2C%204%2C%205%5D">Try this <strong>R.union</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptunion<T>(x: T[], y: T[]): T[];union<T>(x: T[]): (y: T[]) => T[];```
</details><details><summary><strong>R.union</strong> source</summary>```javascriptimport { cloneList } from './_internals/cloneList.js'import { includes } from './includes.js'
export function union(x, y){ if (arguments.length === 1) return _y => union(x, _y) const toReturn = cloneList(x) y.forEach(yInstance => { if (!includes(yInstance, x)) toReturn.push(yInstance) }) return toReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { union } from './union.js'
test('happy', () => { expect(union([ 1, 2 ], [ 2, 3 ])).toEqual([ 1, 2, 3 ])})
test('with list of objects', () => { const list1 = [ { a : 1 }, { a : 2 } ] const list2 = [ { a : 2 }, { a : 3 } ] const result = union(list1)(list2)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {union} from 'rambda'
describe('R.union', () => { it('happy', () => { const result = union([1, 2], [2, 3]) result // $ExpectType number[] }) it('with array of objects - case 1', () => { const list1 = [{a: 1}, {a: 2}] const list2 = [{a: 2}, {a: 3}] const result = union(list1, list2) result // $ExpectType { a: number; }[] }) it('with array of objects - case 2', () => { const list1 = [{a: 1, b: 1}, {a: 2}] const list2 = [{a: 2}, {a: 3, b: 3}] const result = union(list1, list2) result[0].a // $ExpectType number result[0].b // $ExpectType number | undefined })})
describe('R.union - curried', () => { it('happy', () => { const result = union([1, 2])([2, 3]) result // $ExpectType number[] }) it('with array of objects - case 1', () => { const list1 = [{a: 1}, {a: 2}] const list2 = [{a: 2}, {a: 3}] const result = union(list1)(list2) result // $ExpectType { a: number; }[] }) it('with array of objects - case 2', () => { const list1 = [{a: 1, b: 1}, {a: 2}] const list2 = [{a: 2}, {a: 3, b: 3}] const result = union(list1)(list2) result[0].a // $ExpectType number result[0].b // $ExpectType number | undefined })})```
</details>[](#union)
### uniq
```typescript
uniq<T>(list: T[]): T[]```
It returns a new array containing only one copy of each element of `list`.
`R.equals` is used to determine equality.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B1%2C%201%2C%20%7Ba%3A%201%7D%2C%20%7Ba%3A%202%7D%2C%20%7Ba%3A1%7D%5D%0A%0Aconst%20result%20%3D%20R.uniq(list)%0A%2F%2F%20%3D%3E%20%5B1%2C%20%7Ba%3A%201%7D%2C%20%7Ba%3A%202%7D%5D">Try this <strong>R.uniq</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptuniq<T>(list: T[]): T[];```
</details><details><summary><strong>R.uniq</strong> source</summary>```javascriptimport { _Set } from './_internals/set.js'
export function uniq(list){ const set = new _Set() const willReturn = [] list.forEach(item => { if (set.checkUniqueness(item)){ willReturn.push(item) } }) return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { uniq } from './uniq.js'
test('happy', () => { const list = [ 1, 2, 3, 3, 3, 1, 2, 0 ] expect(uniq(list)).toEqual([ 1, 2, 3, 0 ])})
test('with object', () => { const list = [ { a : 1 }, { a : 2 }, { a : 1 }, { a : 2 } ] expect(uniq(list)).toEqual([ { a : 1 }, { a : 2 } ])})
test('with nested array', () => { expect(uniq([ [ 42 ], [ 42 ] ])).toEqual([ [ 42 ] ])})
test('with booleans', () => { expect(uniq([ [ false ], [ false ], [ true ] ])).toEqual([ [ false ], [ true ] ])})
test('with falsy values', () => { expect(uniq([ undefined, null ])).toEqual([ undefined, null ])})
test('can distinct between string and number', () => { expect(uniq([ 1, '1' ])).toEqual([ 1, '1' ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {uniq} from 'rambda'
describe('R.uniq', () => { it('happy', () => { const result = uniq([1, 2, 3, 3, 3, 1, 2, 0]) result // $ExpectType number[] })})```
</details>[](#uniq)
### uniqBy
It applies uniqueness to input list based on function that defines what to be used for comparison between elements.
`R.equals` is used to determine equality.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%2C%20%7Ba%3A1%7D%5D%0Aconst%20result%20%3D%20R.uniqBy(x%20%3D%3E%20x%2C%20list)%0A%0A%2F%2F%20%3D%3E%20%5B%7Ba%3A1%7D%2C%20%7Ba%3A2%7D%5D">Try this <strong>R.uniqBy</strong> example in Rambda REPL</a>[](#uniqBy)
### uniqWith
```typescript
uniqWith<T, U>(predicate: (x: T, y: T) => boolean, list: T[]): T[]```
It returns a new array containing only one copy of each element in `list` according to `predicate` function.
This predicate should return true, if two elements are equal.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list%20%3D%20%5B%0A%20%20%7Bid%3A%200%2C%20title%3A'foo'%7D%2C%0A%20%20%7Bid%3A%201%2C%20title%3A'bar'%7D%2C%0A%20%20%7Bid%3A%202%2C%20title%3A'baz'%7D%2C%0A%20%20%7Bid%3A%203%2C%20title%3A'foo'%7D%2C%0A%20%20%7Bid%3A%204%2C%20title%3A'bar'%7D%2C%0A%5D%0A%0Aconst%20expected%20%3D%20%5B%0A%20%20%7Bid%3A%200%2C%20title%3A'foo'%7D%2C%0A%20%20%7Bid%3A%201%2C%20title%3A'bar'%7D%2C%0A%20%20%7Bid%3A%202%2C%20title%3A'baz'%7D%2C%0A%5D%0A%0Aconst%20predicate%20%3D%20(x%2Cy)%20%3D%3E%20x.title%20%3D%3D%3D%20y.title%0A%0Aconst%20result%20%3D%20R.uniqWith(predicate%2C%20list)%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.uniqWith</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptuniqWith<T, U>(predicate: (x: T, y: T) => boolean, list: T[]): T[];uniqWith<T, U>(predicate: (x: T, y: T) => boolean): (list: T[]) => T[];```
</details><details><summary><strong>R.uniqWith</strong> source</summary>```javascriptfunction includesWith( predicate, target, list){ let willReturn = false let index = -1 while (++index < list.length && !willReturn){ const value = list[ index ] if (predicate(target, value)){ willReturn = true } } return willReturn}
export function uniqWith(predicate, list){ if (arguments.length === 1) return _list => uniqWith(predicate, _list) let index = -1 const willReturn = [] while (++index < list.length){ const value = list[ index ] if (!includesWith( predicate, value, willReturn )){ willReturn.push(value) } } return willReturn}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { uniqWith as uniqWithRamda } from 'ramda'
import { uniqWith } from './uniqWith.js'
const list = [ { a : 1 }, { a : 1 } ]
test('happy', () => { const fn = (x, y) => x.a === y.a const result = uniqWith(fn, list) expect(result).toEqual([ { a : 1 } ])})
test('with list of strings', () => { const fn = (x, y) => x.length === y.length const list = [ '0', '11', '222', '33', '4', '55' ] const result = uniqWith(fn)(list) const resultRamda = uniqWithRamda(fn, list) expect(result).toEqual([ '0', '11', '222' ]) expect(resultRamda).toEqual([ '0', '11', '222' ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {uniqWith} from 'rambda'
describe('R.uniqWith', () => { it('happy', () => { const list = [{a: 1}, {a: 1}] const fn = (x: any, y: any) => x.a === y.a const result = uniqWith(fn, list) result // $ExpectType { a: number; }[] })})```
</details>[](#uniqWith)
### unless
```typescript
unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, x: T): T | U```
The method returns function that will be called with argument `input`.
If `predicate(input)` returns `false`, then the end result will be the outcome of `whenFalse(input)`.
In the other case, the final output will be the `input` itself.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20fn%20%3D%20R.unless(%0A%20%20x%20%3D%3E%20x%20%3E%202%2C%0A%20%20x%20%3D%3E%20x%20%2B%2010%0A)%0A%0Aconst%20result%20%3D%20%5B%0A%20%20fn(1)%2C%0A%20%20fn(5)%0A%5D%0A%2F%2F%20%3D%3E%20%5B11%2C%205%5D">Try this <strong>R.unless</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptunless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, x: T): T | U;unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U): (x: T) => T | U;unless<T>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => T, x: T): T;unless<T>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => T): (x: T) => T;```
</details><details><summary><strong>R.unless</strong> source</summary>```javascriptexport function unless(predicate, whenFalse){ if (arguments.length === 1){ return _whenFalse => unless(predicate, _whenFalse) } return input => predicate(input) ? input : whenFalse(input)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { inc } from './inc.js'import { isNil } from './isNil.js'import { unless } from './unless.js'
test('happy', () => { const safeInc = unless(isNil, inc) expect(safeInc(null)).toBeNull() expect(safeInc(1)).toBe(2)})
test('curried', () => { const safeIncCurried = unless(isNil)(inc) expect(safeIncCurried(null)).toBeNull()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {unless, inc} from 'rambda'
describe('R.unless', () => { it('happy', () => { const fn = unless(x => x > 5, inc) const result = fn(1) result // $ExpectType number }) it('with one explicit type', () => { const result = unless( x => { x // $ExpectType number return x > 5 }, x => { x // $ExpectType number return x + 1 }, 1 ) result // $ExpectType number }) it('with two different explicit types', () => { const result = unless( x => { x // $ExpectType number return x > 5 }, x => { x // $ExpectType number return `${x}-foo` }, 1 ) result // $ExpectType string | number })})
describe('R.unless - curried', () => { it('happy', () => { const fn = unless(x => x > 5, inc) const result = fn(1) result // $ExpectType number }) it('with one explicit type', () => { const fn = unless<number>( x => { x // $ExpectType number return x > 5 }, x => { x // $ExpectType number return x + 1 } ) const result = fn(1) result // $ExpectType number }) it('with two different explicit types', () => { const fn = unless<number, string>( x => { x // $ExpectType number return x > 5 }, x => { x // $ExpectType number return `${x}-foo` } ) const result = fn(1) result // $ExpectType string | number })})```
</details>[](#unless)
### unnest
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20R.unnest(%5B1%2C%20%5B2%5D%2C%20%5B%5B3%5D%5D%5D)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%20%5B3%5D%5D">Try this <strong>R.unnest</strong> example in Rambda REPL</a>[](#unnest)
### unwind
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7B%0A%20%20a%3A%201%2C%0A%20%20b%3A%20%5B2%2C%203%5D%2C%0A%7D%0Aconst%20result%20%3D%20R.unwind('b'%2C%20obj)%0Aconst%20expected%20%3D%20%5B%7Ba%3A1%2C%20b%3A2%7D%2C%20%7Ba%3A1%2C%20b%3A3%7D%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.unwind</strong> example in Rambda REPL</a>[](#unwind)
### update
```typescript
update<T>(index: number, newValue: T, list: T[]): T[]```
It returns a copy of `list` with updated element at `index` with `newValue`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20index%20%3D%202%0Aconst%20newValue%20%3D%2088%0Aconst%20list%20%3D%20%5B1%2C%202%2C%203%2C%204%2C%205%5D%0A%0Aconst%20result%20%3D%20R.update(index%2C%20newValue%2C%20list)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%2C%2088%2C%204%2C%205%5D">Try this <strong>R.update</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptupdate<T>(index: number, newValue: T, list: T[]): T[];update<T>(index: number, newValue: T): (list: T[]) => T[];```
</details><details><summary><strong>R.update</strong> source</summary>```javascriptimport { cloneList } from './_internals/cloneList.js'import { curry } from './curry.js'
export function updateFn( index, newValue, list){ const clone = cloneList(list) if (index === -1) return clone.fill(newValue, index) return clone.fill( newValue, index, index + 1 )}
export const update = curry(updateFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { update } from './update.js'
const list = [ 1, 2, 3 ]
test('happy', () => { const newValue = 8 const index = 1 const result = update( index, newValue, list ) const curriedResult = update(index, newValue)(list) const tripleCurriedResult = update(index)(newValue)(list) const expected = [ 1, 8, 3 ] expect(result).toEqual(expected) expect(curriedResult).toEqual(expected) expect(tripleCurriedResult).toEqual(expected)})
test('list has no such index', () => { const newValue = 8 const index = 10 const result = update( index, newValue, list ) expect(result).toEqual(list)})
test('with negative index', () => { expect(update( -1, 10, [ 1 ] )).toEqual([ 10 ]) expect(update( -1, 10, [] )).toEqual([]) expect(update( -1, 10, list )).toEqual([ 1, 2, 10 ]) expect(update( -2, 10, list )).toEqual([ 1, 10, 3 ]) expect(update( -3, 10, list )).toEqual([ 10, 2, 3 ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {update} from 'rambda'
describe('R.update', () => { it('happy', () => { const result = update(1, 0, [1, 2, 3]) result // $ExpectType number[] })})```
</details>[](#update)
### values
```typescript
values<T extends object, K extends keyof T>(obj: T): T[K][]```
With correct input, this is nothing more than `Object.values(Record<string, unknown>)`. If `obj` is not an object, then it returns an empty array.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20obj%20%3D%20%7Ba%3A1%2C%20b%3A2%7D%0A%0Aconst%20result%20%3D%20R.values(Record%3Cstring%2C%20unknown%3E)%0A%2F%2F%20%3D%3E%20%5B1%2C%202%5D">Try this <strong>R.values</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptvalues<T extends object, K extends keyof T>(obj: T): T[K][];```
</details><details><summary><strong>R.values</strong> source</summary>```javascriptimport { type } from './type.js'
export function values(obj){ if (type(obj) !== 'Object') return [] return Object.values(obj)}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { values } from './values.js'
test('happy', () => { expect(values({ a : 1, b : 2, c : 3, })).toEqual([ 1, 2, 3 ])})
test('with bad input', () => { expect(values(null)).toEqual([]) expect(values(undefined)).toEqual([]) expect(values(55)).toEqual([]) expect(values('foo')).toEqual([]) expect(values(true)).toEqual([]) expect(values(false)).toEqual([]) expect(values(NaN)).toEqual([]) expect(values(Infinity)).toEqual([]) expect(values([])).toEqual([])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {values} from 'rambda'
describe('R.values', () => { it('happy', () => { const result = values({ a: 1, b: 2, c: 3, }) result // $ExpectType number[] })})```
</details>[](#values)
### view
```typescript
view<S, A>(lens: Lens<S, A>): (obj: S) => A```
It returns the value of `lens` focus over `target` object.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20lens%20%3D%20R.lensProp('x')%0A%0AR.view(lens%2C%20%7Bx%3A%201%2C%20y%3A%202%7D)%20%2F%2F%20%3D%3E%201%0Aconst%20result%20%3D%20R.view(lens%2C%20%7Bx%3A%204%2C%20y%3A%202%7D)%20%2F%2F%20%3D%3E%204">Try this <strong>R.view</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptview<S, A>(lens: Lens<S, A>): (obj: S) => A;view<S, A>(lens: Lens<S, A>, obj: S): A;```
</details><details><summary><strong>R.view</strong> source</summary>```javascriptconst Const = x => ({ x, map : fn => Const(x),})
export function view(lens, target){ if (arguments.length === 1) return _target => view(lens, _target) return lens(Const)(target).x}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { assoc } from './assoc.js'import { lens } from './lens.js'import { prop } from './prop.js'import { view } from './view.js'
const testObject = { foo : 'Led Zeppelin' }const assocLens = lens(prop('foo'), assoc('foo'))
test('happy', () => { expect(view(assocLens, testObject)).toBe('Led Zeppelin')})```
</details>[](#view)
### when
```typescript
when<T, U>(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U, input: T): T | U```
It pass `input` to `predicate` function and if the result is `true`, it will return the result of `whenTrueFn(input)`. If the `predicate` returns `false`, then it will simply return `input`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20predicate%20%3D%20x%20%3D%3E%20typeof%20x%20%3D%3D%3D%20'number'%0Aconst%20whenTrueFn%20%3D%20R.add(11)%0A%0Aconst%20fn%20%3D%20when(predicate%2C%20whenTrueResult)%0A%0Aconst%20positiveInput%20%3D%2088%0Aconst%20negativeInput%20%3D%20'foo'%0A%0Aconst%20result%20%3D%20%5B%0A%20%20fn(positiveInput)%2C%0A%20%20fn(positiveInput)%2C%0A%5D%0A%0Aconst%20expected%20%3D%20%5B%0A%20%2099%2C%0A%20%20'foo'%2C%0A%5D%0A%2F%2F%20%3D%3E%20%60result%60%20is%20equal%20to%20%60expected%60">Try this <strong>R.when</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptwhen<T, U>(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U, input: T): T | U;when<T, U>(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U): (input: T) => T | U;when<T, U>(predicate: (x: T) => boolean): ((whenTrueFn: (a: T) => U) => (input: T) => T | U);```
</details><details><summary><strong>R.when</strong> source</summary>```javascriptimport { curry } from './curry.js'
function whenFn( predicate, whenTrueFn, input){ if (!predicate(input)) return input return whenTrueFn(input)}
export const when = curry(whenFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { add } from './add.js'import { when } from './when.js'
const predicate = x => typeof x === 'number'
test('happy', () => { const fn = when(predicate, add(11)) expect(fn(11)).toBe(22) expect(fn('foo')).toBe('foo')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {when} from 'rambda'
const predicate = (x: number) => x > 2const whenTrueFn = (x: number) => String(x)
describe('R.when', () => { it('happy', () => { const result = when(predicate, whenTrueFn, 1) result // $ExpectType string | 1 }) it('curry 1', () => { const fn = when(predicate, whenTrueFn) const result = fn(1) result // $ExpectType string | number }) it('curry 2 require explicit types', () => { const fn = when<number, string>(predicate)(whenTrueFn) const result = fn(1) result // $ExpectType string | number })})```
</details>[](#when)
### where
```typescript
where<T, U>(conditions: T, input: U): boolean```
It returns `true` if all each property in `conditions` returns `true` when applied to corresponding property in `input` object.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20condition%20%3D%20R.where(%7B%0A%20%20a%20%3A%20x%20%3D%3E%20typeof%20x%20%3D%3D%3D%20%22string%22%2C%0A%20%20b%20%3A%20x%20%3D%3E%20x%20%3D%3D%3D%204%0A%7D)%0Aconst%20input%20%3D%20%7B%0A%20%20a%20%3A%20%22foo%22%2C%0A%20%20b%20%3A%204%2C%0A%20%20c%20%3A%2011%2C%0A%7D%0A%0Aconst%20result%20%3D%20condition(input)%20%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.where</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptwhere<T, U>(conditions: T, input: U): boolean;where<T>(conditions: T): <U>(input: U) => boolean;where<ObjFunc2, U>(conditions: ObjFunc2, input: U): boolean;where<ObjFunc2>(conditions: ObjFunc2): <U>(input: U) => boolean;```
</details><details><summary><strong>R.where</strong> source</summary>```javascriptexport function where(conditions, input){ if (input === undefined){ return _input => where(conditions, _input) } let flag = true for (const prop in conditions){ if (!flag) continue const result = conditions[ prop ](input[ prop ]) if (flag && result === false){ flag = false } } return flag}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { equals } from './equals.js'import { where } from './where.js'
test('when true', () => { const result = where({ a : equals('foo'), b : equals('bar'), }, { a : 'foo', b : 'bar', x : 11, y : 19, }) expect(result).toBeTrue()})
test('when false | early exit', () => { let counter = 0 const equalsFn = expected => input => { console.log(expected, 'expected') counter++ return input === expected } const predicate = where({ a : equalsFn('foo'), b : equalsFn('baz'), }) expect(predicate({ a : 'notfoo', b : 'notbar', })).toBeFalse() expect(counter).toBe(1)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {where, equals} from 'rambda'
describe('R.where', () => { it('happy', () => { const input = { a: 'foo', b: 'bar', x: 11, y: 19, } const conditions = { a: equals('foo'), b: equals('bar'), } const result = where(conditions, input) const curriedResult = where(conditions)(input) result // $ExpectType boolean curriedResult // $ExpectType boolean })})```
</details>[](#where)
### whereAny
Same as `R.where`, but it will return `true` if at least one condition check returns `true`.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20conditions%20%3D%20%7B%0A%20%20a%3A%20a%20%3D%3E%20a%20%3E%201%2C%0A%20%20b%3A%20b%20%3D%3E%20b%20%3E%202%2C%0A%7D%0Aconst%20result%20%3D%20%5B%0A%20%20R.whereAny(conditions%2C%20%7Bb%3A3%7D)%2C%0A%20%20R.whereAny(conditions%2C%20%7Bc%3A4%7D)%0A%5D%0A%2F%2F%20%3D%3E%20%5Btrue%2C%20false%5D">Try this <strong>R.whereAny</strong> example in Rambda REPL</a>[](#whereAny)
### whereEq
```typescript
whereEq<T, U>(condition: T, input: U): boolean```
It will return `true` if all of `input` object fully or partially include `rule` object.
`R.equals` is used to determine equality.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20condition%20%3D%20%7B%20a%20%3A%20%7B%20b%20%3A%201%20%7D%20%7D%0Aconst%20input%20%3D%20%7B%0A%20%20a%20%3A%20%7B%20b%20%3A%201%20%7D%2C%0A%20%20c%20%3A%202%0A%7D%0A%0Aconst%20result%20%3D%20whereEq(condition%2C%20input)%0A%2F%2F%20%3D%3E%20true">Try this <strong>R.whereEq</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptwhereEq<T, U>(condition: T, input: U): boolean;whereEq<T>(condition: T): <U>(input: U) => boolean;```
</details><details><summary><strong>R.whereEq</strong> source</summary>```javascriptimport { equals } from './equals.js'import { filter } from './filter.js'
export function whereEq(condition, input){ if (arguments.length === 1){ return _input => whereEq(condition, _input) } const result = filter((conditionValue, conditionProp) => equals(conditionValue, input[ conditionProp ]), condition) return Object.keys(result).length === Object.keys(condition).length}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { whereEq } from './whereEq.js'
test('when true', () => { const condition = { a : 1 } const input = { a : 1, b : 2, } const result = whereEq(condition, input) const expectedResult = true expect(result).toEqual(expectedResult)})
test('when false', () => { const condition = { a : 1 } const input = { b : 2 } const result = whereEq(condition, input) const expectedResult = false expect(result).toEqual(expectedResult)})
test('with nested object', () => { const condition = { a : { b : 1 } } const input = { a : { b : 1 }, c : 2, } const result = whereEq(condition)(input) const expectedResult = true expect(result).toEqual(expectedResult)})
test('with wrong input', () => { const condition = { a : { b : 1 } } expect(() => whereEq(condition, null)).toThrowErrorMatchingInlineSnapshot('"Cannot read properties of null (reading \'a\')"')})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {whereEq} from 'rambda'
describe('R.whereEq', () => { it('happy', () => { const result = whereEq({a: {b: 2}}, {b: 2}) const curriedResult = whereEq({a: {b: 2}})({b: 2}) result // $ExpectType boolean curriedResult // $ExpectType boolean })})```
</details>[](#whereEq)
### without
```typescript
without<T>(matchAgainst: T[], source: T[]): T[]```
It will return a new array, based on all members of `source` list that are not part of `matchAgainst` list.
`R.equals` is used to determine equality.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20source%20%3D%20%5B1%2C%202%2C%203%2C%204%5D%0Aconst%20matchAgainst%20%3D%20%5B2%2C%203%5D%0A%0Aconst%20result%20%3D%20R.without(matchAgainst%2C%20source)%0A%2F%2F%20%3D%3E%20%5B1%2C%204%5D">Try this <strong>R.without</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptwithout<T>(matchAgainst: T[], source: T[]): T[];without<T>(matchAgainst: T[]): (source: T[]) => T[];```
</details><details><summary><strong>R.without</strong> source</summary>```javascriptimport { _indexOf } from './equals.js'import { reduce } from './reduce.js'
export function without(matchAgainst, source){ if (source === undefined){ return _source => without(matchAgainst, _source) } return reduce( (prev, current) => _indexOf(current, matchAgainst) > -1 ? prev : prev.concat(current), [], source )}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { without as withoutRamda } from 'ramda'
import { without } from './without.js'
test('should return a new list without values in the first argument', () => { const itemsToOmit = [ 'A', 'B', 'C' ] const collection = [ 'A', 'B', 'C', 'D', 'E', 'F' ] expect(without(itemsToOmit, collection)).toEqual([ 'D', 'E', 'F' ]) expect(without(itemsToOmit)(collection)).toEqual([ 'D', 'E', 'F' ])})
test('with list of objects', () => { const itemsToOmit = [ { a : 1 }, { c : 3 } ] const collection = [ { a : 1 }, { b : 2 }, { c : 3 }, { d : 4 } ] const expected = [ { b : 2 }, { d : 4 } ] expect(without(itemsToOmit, collection)).toEqual(expected) expect(withoutRamda(itemsToOmit, collection)).toEqual(expected)})
test('ramda accepts string as target input while rambda throws', () => { expect(withoutRamda('0:1', [ '0', '0:1' ])).toEqual([ '0:1' ]) expect(() => without('0:1', [ '0', '0:1' ])).toThrowErrorMatchingInlineSnapshot('"Cannot read property \'indexOf\' of 0:1"') expect(without([ '0:1' ], [ '0', '0:1' ])).toEqual([ '0' ])})
test('ramda test', () => { expect(without([ 1, 2 ])([ 1, 2, 1, 3, 4 ])).toEqual([ 3, 4 ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {without} from 'rambda'
const itemsToOmit = ['A', 'B', 'C']const collection = ['A', 'B', 'C', 'D', 'E', 'F']
describe('R.without', () => { it('happy', () => { const result = without(itemsToOmit, collection) result // $ExpectType string[] }) it('curried', () => { const result = without(itemsToOmit)(collection) result // $ExpectType string[] })})```
</details>[](#without)
### xor
```typescript
xor(x: boolean, y: boolean): boolean```
Logical XOR
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20result%20%3D%20%5B%0A%20%20xor(true%2C%20true)%2C%0A%20%20xor(false%2C%20false)%2C%0A%20%20xor(false%2C%20true)%2C%0A%5D%0A%2F%2F%20%3D%3E%20%5Bfalse%2C%20false%2C%20true%5D">Try this <strong>R.xor</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptxor(x: boolean, y: boolean): boolean;xor(y: boolean): (y: boolean) => boolean;```
</details><details><summary><strong>R.xor</strong> source</summary>```javascriptexport function xor(a, b){ if (arguments.length === 1) return _b => xor(a, _b) return Boolean(a) && !b || Boolean(b) && !a}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { xor } from './xor.js'
test('compares two values with exclusive or', () => { expect(xor(true, true)).toBeFalse() expect(xor(true, false)).toBeTrue() expect(xor(false, true)).toBeTrue() expect(xor(false, false)).toBeFalse()})
test('when both values are truthy, it should return false', () => { expect(xor(true, 'foo')).toBeFalse() expect(xor(42, true)).toBeFalse() expect(xor('foo', 42)).toBeFalse() expect(xor({}, true)).toBeFalse() expect(xor(true, [])).toBeFalse() expect(xor([], {})).toBeFalse() expect(xor(new Date(), true)).toBeFalse() expect(xor(true, Infinity)).toBeFalse() expect(xor(Infinity, new Date())).toBeFalse()})
test('when both values are falsy, it should return false', () => { expect(xor(null, false)).toBeFalse() expect(xor(false, undefined)).toBeFalse() expect(xor(undefined, null)).toBeFalse() expect(xor(0, false)).toBeFalse() expect(xor(false, NaN)).toBeFalse() expect(xor(NaN, 0)).toBeFalse() expect(xor('', false)).toBeFalse()})
test('when one argument is truthy and the other is falsy, it should return true', () => { expect(xor('foo', null)).toBeTrue() expect(xor(null, 'foo')).toBeTrue() expect(xor(undefined, 42)).toBeTrue() expect(xor(42, undefined)).toBeTrue() expect(xor(Infinity, NaN)).toBeTrue() expect(xor(NaN, Infinity)).toBeTrue() expect(xor({}, '')).toBeTrue() expect(xor('', {})).toBeTrue() expect(xor(new Date(), 0)).toBeTrue() expect(xor(0, new Date())).toBeTrue() expect(xor([], null)).toBeTrue() expect(xor(undefined, [])).toBeTrue()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {xor} from 'rambda'
describe('R.xor', () => { it('happy', () => { xor(true, false) // $ExpectType boolean }) it('curry', () => { xor(true)(false) // $ExpectType boolean })})```
</details>[](#xor)
### zip
```typescript
zip<K, V>(x: K[], y: V[]): KeyValuePair<K, V>[]```
It will return a new array containing tuples of equally positions items from both `x` and `y` lists.
The returned list will be truncated to match the length of the shortest supplied list.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20x%20%3D%20%5B1%2C%202%5D%0Aconst%20y%20%3D%20%5B'A'%2C%20'B'%5D%0AR.zip(x%2C%20y)%0A%2F%2F%20%3D%3E%20%5B%5B1%2C%20'A'%5D%2C%20%5B2%2C%20'B'%5D%5D%0A%0A%2F%2F%20truncates%20to%20shortest%20list%0Aconst%20result%20%3D%20R.zip(%5B...x%2C%203%5D%2C%20%5B'A'%2C%20'B'%5D)%0A%2F%2F%20%3D%3E%20%5B%5B1%2C%20'A'%5D%2C%20%5B2%2C%20'B'%5D%5D">Try this <strong>R.zip</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptzip<K, V>(x: K[], y: V[]): KeyValuePair<K, V>[];zip<K>(x: K[]): <V>(y: V[]) => KeyValuePair<K, V>[];```
</details><details><summary><strong>R.zip</strong> source</summary>```javascriptexport function zip(left, right){ if (arguments.length === 1) return _right => zip(left, _right) const result = [] const length = Math.min(left.length, right.length) for (let i = 0; i < length; i++){ result[ i ] = [ left[ i ], right[ i ] ] } return result}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { zip } from './zip.js'
const array1 = [ 1, 2, 3 ]const array2 = [ 'A', 'B', 'C' ]
test('should return an array', () => { const actual = zip(array1)(array2) expect(actual).toBeInstanceOf(Array)})
test('should return and array or tuples', () => { const expected = [ [ 1, 'A' ], [ 2, 'B' ], [ 3, 'C' ], ] const actual = zip(array1, array2) expect(actual).toEqual(expected)})
test('should truncate result to length of shorted input list', () => { const expectedA = [ [ 1, 'A' ], [ 2, 'B' ], ] const actualA = zip([ 1, 2 ], array2) expect(actualA).toEqual(expectedA) const expectedB = [ [ 1, 'A' ], [ 2, 'B' ], ] const actualB = zip(array1, [ 'A', 'B' ]) expect(actualB).toEqual(expectedB)})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {zip} from 'rambda'
describe('R.zip', () => { it('happy', () => { const array1 = [1, 2, 3] const array2 = ['A', 'B', 'C'] const result = zip(array1)(array2) result // $ExpectType KeyValuePair<number, string>[] })})```
</details>[](#zip)
### zipObj
```typescript
zipObj<T, K extends string>(keys: K[], values: T[]): { [P in K]: T }```
It will return a new object with keys of `keys` array and values of `values` array.
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20keys%20%3D%20%5B'a'%2C%20'b'%2C%20'c'%5D%0A%0AR.zipObj(keys%2C%20%5B1%2C%202%2C%203%5D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%201%2C%20b%3A%202%2C%20c%3A%203%7D%0A%0A%2F%2F%20truncates%20to%20shortest%20list%0Aconst%20result%20%3D%20R.zipObj(keys%2C%20%5B1%2C%202%5D)%0A%2F%2F%20%3D%3E%20%7Ba%3A%201%2C%20b%3A%202%7D">Try this <strong>R.zipObj</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptzipObj<T, K extends string>(keys: K[], values: T[]): { [P in K]: T };zipObj<K extends string>(keys: K[]): <T>(values: T[]) => { [P in K]: T };zipObj<T, K extends number>(keys: K[], values: T[]): { [P in K]: T };zipObj<K extends number>(keys: K[]): <T>(values: T[]) => { [P in K]: T };```
</details><details><summary><strong>R.zipObj</strong> source</summary>```javascriptimport { take } from './take.js'
export function zipObj(keys, values){ if (arguments.length === 1) return yHolder => zipObj(keys, yHolder) return take(values.length, keys).reduce(( prev, xInstance, i ) => { prev[ xInstance ] = values[ i ] return prev }, {})}```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { equals } from './equals.js'import { zipObj } from './zipObj.js'
test('zipObj', () => { expect(zipObj([ 'a', 'b', 'c' ], [ 1, 2, 3 ])).toEqual({ a : 1, b : 2, c : 3, })})
test('0', () => { expect(zipObj([ 'a', 'b' ])([ 1, 2, 3 ])).toEqual({ a : 1, b : 2, })})
test('1', () => { expect(zipObj([ 'a', 'b', 'c' ])([ 1, 2 ])).toEqual({ a : 1, b : 2, })})
test('ignore extra keys', () => { const result = zipObj([ 'a', 'b', 'c', 'd', 'e', 'f' ], [ 1, 2, 3 ]) const expected = { a : 1, b : 2, c : 3, } expect(equals(result, expected)).toBeTrue()})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {zipObj} from 'rambda'
describe('R.zipObj', () => { it('happy', () => { // this is wrong since 24.10.2020 `@types/ramda` changes const result = zipObj(['a', 'b', 'c', 'd'], [1, 2, 3]) ;[result.a, result.b, result.c, result.d] // $ExpectType number[] }) it('imported from @types/ramda', () => { const result = zipObj(['a', 'b', 'c'], [1, 2, 3]) const curriedResult = zipObj(['a', 'b', 'c'])([1, 2, 3]) ;[result.a, result.b, result.c] // $ExpectType number[] ;[curriedResult.a, curriedResult.b, curriedResult.c] // $ExpectType number[] })})```
</details>[](#zipObj)
### zipWith
```typescript
zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult, list1: T[], list2: U[]): TResult[]```
<a title="redirect to Rambda Repl site" href="https://rambda.now.sh?const%20list1%20%3D%20%5B%2010%2C%2020%2C%2030%2C%2040%20%5D%0Aconst%20list2%20%3D%20%5B%20100%2C%20200%20%5D%0A%0Aconst%20result%20%3D%20R.zipWith(%0A%20%20R.add%2C%20list1%2C%20list2%0A)%0A%2F%2F%20%3D%3E%20%5B110%2C%20220%5D">Try this <strong>R.zipWith</strong> example in Rambda REPL</a><details><summary>All TypeScript definitions</summary>```typescriptzipWith<T, U, TResult>(fn: (x: T, y: U) => TResult, list1: T[], list2: U[]): TResult[];zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult, list1: T[]): (list2: U[]) => TResult[];zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult): (list1: T[], list2: U[]) => TResult[];```
</details><details><summary><strong>R.zipWith</strong> source</summary>```javascriptimport { curry } from './curry.js'import { take } from './take.js'
function zipWithFn( fn, x, y){ return take(x.length > y.length ? y.length : x.length, x).map((xInstance, i) => fn(xInstance, y[ i ]))}
export const zipWith = curry(zipWithFn)```
</details><details><summary><strong>Tests</strong></summary>```javascriptimport { add } from './add.js'import { zipWith } from './zipWith.js'
const list1 = [ 1, 2, 3 ]const list2 = [ 10, 20, 30, 40 ]const list3 = [ 100, 200 ]
test('when second list is shorter', () => { const result = zipWith( add, list1, list3 ) expect(result).toEqual([ 101, 202 ])})
test('when second list is longer', () => { const result = zipWith( add, list1, list2 ) expect(result).toEqual([ 11, 22, 33 ])})```
</details><details><summary><strong>TypeScript</strong> test</summary>```typescriptimport {zipWith} from 'rambda'
const list1 = [1, 2]const list2 = [10, 20, 30]
describe('R.zipWith', () => { it('happy', () => { const result = zipWith( (x, y) => { x // $ExpectType number y // $ExpectType number return `${x}-${y}` }, list1, list2 ) result // $ExpectType string[] }) it('curried', () => { const result = zipWith((x, y) => { x // $ExpectType unknown y // $ExpectType unknown return `${x}-${y}` })(list1, list2) result // $ExpectType string[] })})```
</details>[](#zipWith)
## ❯ CHANGELOG
9.1.1
- Faster R.equals with Object.is short circuit - https://github.com/selfrefactor/rambda/pull/725- Fix R.cond transform is unary - https://github.com/selfrefactor/rambda/issues/7209.1.0
Add these methods
- insert- insertAll- lt- lte- isNotNil- pickBy- pathSatisfies- swap- mergeDeepLeft9.0.1
- Fix bad TS typings, due to missing declaration - [Issue #716](https://github.com/selfrefactor/rambda/issues/716)9.0.0
Breaking change in TS definitions of `lenses` as now they are synced to `Ramda` types.
- Add `R.sortWith` - [Issue #707](https://github.com/selfrefactor/rambda/issues/707)- Add `R.innerJoin`, `R.gt`, `R.gte`, `R.reduceBy`, `R.hasIn`8.6.0
- Wrong typing for `R.dissocPath` - [Issue #709](https://github.com/selfrefactor/rambda/issues/709)- Update build dependencies8.5.0
- Revert changes in `R.anyPass` introduced in `8.4.0` release. The reason is that the change was breaking the library older than `5.2.0` TypeScript.- Wrong `R.partial` TS definition - [Issue #705](https://github.com/selfrefactor/rambda/issues/705)- Add `R.dropRepeatsBy`- Add `R.empty`- Add `R.eqBy`- Add `R.forEachObjIndexed`8.4.0
- Add `R.dissocPath`- Fix TS definitions of `R.head/R.last` and add missing handle of empty string- Add `R.removeIndex` - method was before only in `Rambdax`, but now since `R.dissocPath` is using it, it is added to main library.- Allow `R.omit` to pass numbers as part of properties to omit, i.e. `R.omit(['a', 1], {a: {1: 1, 2: 2}})`- R.keys always returns strings - [MR #700](https://github.com/selfrefactor/rambda/pull/700)- Improve `R.prepend/R.append` type interference - [MR #699](https://github.com/selfrefactor/rambda/pull/699)- Change `R.reduce` TS definitions so index is always received - [MR #696](https://github.com/selfrefactor/rambda/pull/696)- Functions as a type guard in `R.anyPass` TS definitions - [MR #695](https://github.com/selfrefactor/rambda/pull/695)- Fix R.append's curried type - [MR #694](https://github.com/selfrefactor/rambda/pull/694)- Fix cannot compare errors in `Deno` with `R.equals` - [Issue #704](https://github.com/selfrefactor/rambda/issues/704).- Fix cannot compare `BigInt` with `R.equals` 8.3.0
Add the following methods:
- binary- call- collectBy- comparator- composeWith8.2.0
Add the following methods:
- addIndex- addIndexRight- ap- aperture- applyTo- ascend- descend8.1.0
- Fix input order of TS definitions for `R.propEq` method - [Issue #688](https://github.com/selfrefactor/rambda/issues/688). The issue was due to 8.0.0 was shipped with TS definitions of `7.5.0` release.- Add `R.differenceWith` method - [Issue #91](https://github.com/selfrefactor/rambdax/issues/91)8.0.0
- handle falsy values in merge methods - https://github.com/ramda/ramda/pull/3222- `R.head`/`R.last` don't return `undefined` for non-empty arrays- `R.type` supports dates in TS definition - `Rambda` already did support dates in JS.- Improve typings of `R.endsWith/startsWith` with regard to `string` input. - [PR #622](https://github.com/selfrefactor/rambda/pull/622)- Handle list as falsy value in `R.reduce` - [Ramda MR](https://github.com/ramda/ramda/pull/2997/files)- `R.nop` is removed - it will be moved to `Rambdax` as `R.noop`- `R.includes` is no longer using string literal in TypeScript definitions> Reason for breaking change - synchronize with Ramda `0.29.0` release:- change order of `R.propEq` - [Ramda MR](https://github.com/ramda/ramda/pull/2938/files)7.5.0
- IMPORTANT: Remove `export` property in `package.json` in order to allow `Rambda` support for projects with `"type": "module"` in `package.json` - [Issue #667](https://github.com/selfrefactor/rambda/issues/657)- Add `R.unnest` - [Rambdax issue 89](https://github.com/selfrefactor/rambdax/issues/89)- `R.uniq` is not using `R.equals` as Ramda does - [Issue #88](https://github.com/selfrefactor/rambdax/issues/88)- Fix `R.path(['non','existing','path'], obj)` TS definition as 7.4.0 release caused TS errors - [Issue #668](https://github.com/selfrefactor/rambda/issues/668)7.4.0
- Synchronize with `@types/ramda` - `R.prop`, `R.path`, `R.pickAll`- Remove `esm` Rollup output due to tree-shaking issues.- Upgrade all dev dependencies.7.3.0
- Important - changing import declaration in `package.json` in order to fix tree-shaking issue - [Issue #647](https://github.com/selfrefactor/rambda/issues/647)- Add `R.modify`- Allow multiple inputs in TypeScript versions of `R.anyPass` and `R.allPass` - [Issue #642](https://github.com/selfrefactor/rambda/issues/604)- Using wrong clone of object in `R.mergeDeepRight` - [Issue #650](https://github.com/selfrefactor/rambda/issues/650)- Missing early return in `R.where` - [Issue #648](https://github.com/selfrefactor/rambda/issues/648)- `R.allPass` doesn't accept more than 1 parameters for function predicates- [Issue #604](https://github.com/selfrefactor/rambda/issues/604)7.2.1
- Remove bad typings of `R.propIs` which caused the library to cannot be build with TypeScript. - Drop support for `Wallaby` as per [https://github.com/wallabyjs/public/issues/3037](https://github.com/wallabyjs/public/issues/3037)7.2.0
- Wrong `R.update` if index is `-1` - [PR #593](https://github.com/selfrefactor/rambda/pull/593)- Wrong curried typings in `R.anyPass` - [Issue #642](https://github.com/selfrefactor/rambda/issues/642)- `R.modifyPath` not exported - [Issue #640](https://github.com/selfrefactor/rambda/issues/640)- Add new method `R.uniqBy`. Implementation is coming from [Ramda MR#2641](https://github.com/ramda/ramda/pull/2641)- Apply the following changes from `@types/rambda`:-- [https://github.com/DefinitelyTyped/DefinitelyTyped/commit/bab47272d52fc7bb81e85da36dbe9c905a04d067](add `AnyFunction` and `AnyConstructor`)-- Improve `R.ifElse` typings - https://github.com/DefinitelyTyped/DefinitelyTyped/pull/59291-- Make `R.propEq` safe for `null/undefined` arguments - https://github.com/ramda/ramda/pull/2594/files7.1.4
- `R.mergeRight` not found on `Deno` import - [Issue #633](https://github.com/selfrefactor/rambda/issues/633)7.1.0
- Add `R.mergeRight` - introduced by Ramda's latest release. While Ramda renames `R.merge`, Rambda will keep `R.merge`.- Rambda's `pipe/compose` doesn't return proper length of composed function which leads to issue with `R.applySpec`. It was fixed by using Ramda's `pipe/compose` logic - [Issue #627](https://github.com/selfrefactor/rambda/issues/627)- Replace `Async` with `Promise` as return type of `R.type`.- Add new types as TypeScript output for `R.type` - "Map", "WeakMap", "Generator", "GeneratorFunction", "BigInt", "ArrayBuffer"- Add `R.juxt` method- Add `R.propSatisfies` method- Add new methods after `Ramda` version upgrade to `0.28.0`:-- R.count-- R.modifyPath-- R.on-- R.whereAny-- R.partialObject7.0.3
Rambda.none has wrong logic introduced in version `7.0.0` - [Issue #625](https://github.com/selfrefactor/rambda/issues/625)
7.0.2
Rambda doesn't work with `pnpm` due to wrong export configuration - [Issue #619](https://github.com/selfrefactor/rambda/issues/619)
7.0.1
- Wrong ESM export configuration in `package.json` - [Issue #614](https://github.com/selfrefactor/rambda/issues/614)7.0.0
- Breaking change - sync `R.compose`/`R.pipe` with `@types/ramda`. That is significant change so as safeguard, it will lead a major bump. Important - this lead to raising required TypeScript version to `4.2.2`. In other words, to use `Rambda` you'll need TypeScript version `4.2.2` or newer.Related commit in `@types/ramda` - https://github.com/DefinitelyTyped/DefinitelyTyped/commit/286eff4f76d41eb8f091e7437eabd8a60d97fc1f#diff-4f74803fa83a81e47cb17a7d8a4e46a7e451f4d9e5ce2f1bd7a70a72d91f4bc1
There are several other changes in `@types/ramda` as stated in [this comment](https://github.com/ramda/ramda/issues/2976#issuecomment-990408945). This leads to change of typings for the following methods in **Rambda**:
-- R.unless-- R.toString-- R.ifElse-- R.always-- R.complement-- R.cond-- R.is-- R.sortBy-- R.dissoc-- R.toPairs-- R.assoc-- R.toLower-- R.toUpper- One more reason for the breaking change is changing of export declarations in `package.json` based on [this blog post](https://devblogs.microsoft.com/typescript/announcing-typescript-4-5-beta/#packagejson-exports-imports-and-self-referencing) and [this merged Ramda's PR](https://github.com/ramda/ramda/pull/2999). This also led to renaming of `babel.config.js` to `babel.config.cjs`. - Add `R.apply`, `R.bind` and `R.unapply`- `R.startsWith/R.endsWith` now support lists as inputs. This way, it matches current Ramda behavior. - Remove unused typing for `R.chain`.- `R.map`/`R.filter` no longer accept bad inputs as iterable. This way, Rambda behaves more like Ramda, which also throws.- Make `R.lastIndexOf` follow the logic of `R.indexOf`.- Change `R.type` logic to Ramda logic. This way, `R.type` can return `Error` and `Set` as results.- Add missing logic in `R.equals` to compare sets - [Issue #599](https://github.com/selfrefactor/rambda/issues/599)- Improve list cloning - [Issue #595](https://github.com/selfrefactor/rambda/issues/595)- Handle multiple inputs with `R.allPass` and `R.anyPass` - [Issue #604](https://github.com/selfrefactor/rambda/issues/604)- Fix `R.length` wrong logic with inputs as `{length: 123}` - [Issue #606](https://github.com/selfrefactor/rambda/issues/606).- Improve non-curry typings of `R.merge` by using types from [mobily/ts-belt](https://github.com/mobily/ts-belt).- Improve performance of `R.uniqWith`.- Wrong `R.update` if index is `-1` - [PR #593](https://github.com/selfrefactor/rambda/pull/593)- Make `R.eqProps` safe for falsy inputs - based on [this opened Ramda PR](https://github.com/ramda/ramda/pull/2943).- Incorrect benchmarks for `R.pipe/R.compose` - [Issue #608](https://github.com/selfrefactor/rambda/issues/608)- Fix `R.last/R.head` typings - [Issue #609](https://github.com/selfrefactor/rambda/issues/609) 6.9.0
- Fix slow `R.uniq` methods - [Issue #581](https://github.com/selfrefactor/rambda/issues/581)Fixing `R.uniq` was done by improving `R.indexOf` which has performance implication to all methods importing `R.indexOf`:
- R.includes- R.intersection- R.difference- R.excludes- R.symmetricDifference- R.union- R.without no longer support the following case - `without('0:1', ['0', '0:1']) // => ['0']`. Now it throws as the first argument should be a list, not a string. Ramda, on the other hand, returns an empty list - https://github.com/ramda/ramda/issues/3086. 6.8.3
- Fix TypeScript build process with `rambda/immutable` - [Issue #572](https://github.com/selfrefactor/rambda/issues/572)- Add `R.objOf` method- Add `R.mapObjIndexed` method- Publish shorter README.md version to NPM6.8.0
- `R.has` use `Object.prototype.hasOwnProperty`- [Issue #572](https://github.com/selfrefactor/rambda/issues/572)- Expose `immutable.ts` typings which are Rambda typings with `readonly` statements - [Issue #565](https://github.com/selfrefactor/rambda/issues/565)- Fix `R.intersection` wrong order compared to Ramda.- `R.path` wrong return of `null` instead of `undefined` when path value is `null` - [PR #577](https://github.com/selfrefactor/rambda/pull/577)6.7.0
- Remove `ts-toolbelt` types from TypeScript definitions. Most affected are the following methods, which lose one of its curried definitions:1. R.maxBy2. R.minBy3. R.pathEq4. R.viewOr5. R.when6. R.merge7. R.mergeDeepRight8. R.mergeLeft
6.6.0
- Change `R.piped` typings to mimic that of `R.pipe`. Main difference is that `R.pipe` is focused on unary functions.- Fix wrong logic when `R.without` use `R.includes` while it should use array version of `R.includes`.- Use uglify plugin for UMD bundle.- Remove `dist` folder from `.gitignore` in order to fix `Deno` broken package. [Issue #570](https://github.com/selfrefactor/rambda/issues/570)- Improve `R.fromPairs` typings - [Issue #567](https://github.com/selfrefactor/rambda/issues/567)6.5.3
- Wrong logic where `R.without` use `R.includes` while it should use the array version of `R.includes`This is Ramda bug, that Rambda also has before this release - https://github.com/ramda/ramda/issues/3086
6.5.2
- Wrong `R.defaultTo` typings - changes introduced in v6.5.0 are missing their TS equivalent.- Update dependencies6.5.1
Fix wrong versions in changelog
6.5.0
- `R.defaultTo` no longer accepts infinite inputs, thus it follows Ramda implementation.- `R.equals` supports equality of functions.- `R.pipe` doesn't use `R.compose`.- Close [Issue #561](https://github.com/selfrefactor/rambda/issues/561) - export several internal TS interfaces and types- Close [Issue #559](https://github.com/selfrefactor/rambda/issues/559) - improve `R.propOr` typings- Add `CHANGELOG.md` file in release files list> This is only part of the changelog. You can read the full text in [CHANGELOG.md](CHANGELOG.md) file.[](#-changelog)
## ❯ Additional info
> Most influential contributors(in alphabetical order)-  [@farwayer](https://github.com/farwayer) - improving performance in R.find, R.filter; give the idea how to make benchmarks more reliable;-  [@thejohnfreeman](https://github.com/thejohnfreeman) - add R.assoc, R.chain;-  [@peeja](https://github.com/peeja) - add several methods and fix mutiple issues; provides great MR documentation-  [@helmuthdu](https://github.com/helmuthdu) - add R.clone; help improve code style;-  [@jpgorman](https://github.com/jpgorman) - add R.zip, R.reject, R.without, R.addIndex;-  [@ku8ar](https://github.com/ku8ar) - add R.slice, R.propOr, R.identical, R.propIs and several math related methods; introduce the idea to display missing Ramda methods;-  [@romgrk](https://github.com/romgrk) - add R.groupBy, R.indexBy, R.findLast, R.findLastIndex;-  [@squidfunk](https://github.com/squidfunk) - add R.assocPath, R.symmetricDifference, R.difference, R.intersperse;-  [@synthet1c](https://github.com/synthet1c) - add all lenses methods; add R.applySpec, R.converge;-  [@vlad-zhukov](https://github.com/vlad-zhukov) - help with configuring Rollup, Babel; change export file to use ES module exports;> Rambda references- [Interview with Dejan Totef at SurviveJS blog](https://survivejs.com/blog/rambda-interview/)- [Awesome functional Javascript programming libraries](https://github.com/stoeffel/awesome-fp-js#libraries)- [Overview of Rambda pros/cons](https://mobily.github.io/ts-belt/docs/#rambda-%EF%B8%8F)> Links to Rambda- [https://github.com/stoeffel/awesome-fp-js](awesome-fp-js)- [ https://mailchi.mp/webtoolsweekly/web-tools-280 ]( Web Tools Weekly #280 )- [https://github.com/docsifyjs/awesome-docsify](awesome-docsify)> Deprecated from `Used by` section- [SAP's Cloud SDK](https://github.com/SAP/cloud-sdk) - This repo doesn't uses `Rambda` since *October/2020* [commit that removes Rambda](https://github.com/SAP/cloud-sdk/commit/b29b4f915c4e4e9c2441e7b6b67cf83dac1fdac3)[](#-additional-info)
## My other libraries
<table> <tbody> <tr valign="top"> <td width="20%" align="center"> <h4>Niketa theme</h4> <a href="https://marketplace.visualstudio.com/items?itemName=selfrefactor.Niketa-theme">Collection of 9 light VSCode themes</a> </td> <td width="20%" align="center"> <h4>Niketa dark theme</h4> <a href="https://marketplace.visualstudio.com/items?itemName=selfrefactor.niketa-dark-theme">Collection of 9 dark VSCode themes</a> </td> <td width="20%" align="center"> <h4>String-fn</h4> <a href="https://github.com/selfrefactor/services/tree/master/packages/string-fn">String utility library</a> </td> <td width="20%" align="center"> <h4>Useful Javascript libraries</h4> <a href="https://github.com/selfrefactor/useful-javascript-libraries">Large collection of JavaScript,TypeScript and Angular related repos links</a> </td> <td width="20%" align="center"> <h4>Run-fn</h4> <a href="https://github.com/selfrefactor/services/tree/master/packages/run-fn">CLI commands for lint JS/TS files, commit git changes and upgrade of dependencies</a> </td> </tr> </tbody></table>## Stargazers over time
[](https://starchart.cc/selfrefactor/rambda)