std/collections

This module includes utilities around collection types like Array, Record and Set.

Usage

chunked

Splits the given array into chunks of the given size and returns them.

const words = [
  "lorem",
  "ipsum",
  "dolor",
  "sit",
  "amet",
  "consetetur",
  "sadipscing",
];
const chunks = chunked(words, 3);

console.assert(
  chunks === [
    ["lorem", "ipsum", "dolor"],
    ["sit", "amet", "consetetur"],
    ["sadipscing"],
  ],
);

distinctBy

Returns all elements in the given array that produce a distinct value using the given selector, preserving order by first occurence.

const names = ["Anna", "Kim", "Arnold", "Kate"];
const exampleNamesByFirstLetter = distinctBy(names, (it) => it.charAt(0));

console.assert(exampleNamesByFirstLetter === ["Anna", "Kim"]);

distinct

Returns all distinct elements in the given array, preserving order by first occurence.

const numbers = [3, 2, 5, 2, 5];
const distinctNumbers = distinct(numbers);

console.assert(distinctNumbers === [3, 2, 5]);

filterEntries

Returns a new record with all entries of the given record except the ones that do not match the given predicate.

const menu = {
  "Salad": 11,
  "Soup": 8,
  "Pasta": 13,
};
const myOptions = filterEntries(
  menu,
  ([item, price]) => item !== "Pasta" && price < 10,
);
console.assert(
  myOptions === {
    "Soup": 8,
  },
);

filterKeys

Returns a new record with all entries of the given record except the ones that have a key that does not match the given predicate.

const menu = {
  "Salad": 11,
  "Soup": 8,
  "Pasta": 13,
};
const menuWithoutSalad = filterKeys(menu, (it) => it !== "Salad");

console.assert(
  menuWithoutSalad === {
    "Soup": 8,
    "Pasta": 13,
  },
);

filterValues

Returns a new record with all entries of the given record except the ones that have a value that does not match the given predicate.

const people = {
  "Arnold": 37,
  "Sarah": 7,
  "Kim": 23,
};
const adults = filterValues(people, (it) => it.age >= 18);

console.assert(
  adults === {
    "Arnold": 37,
    "Kim": 23,
  },
);

findLast

Returns the last element in the given array matching the given predicate.

const numbers = [4, 2, 7];
const lastEvenNumber = findLast(numbers, (it) => it % 2 === 0);

console.assert(lastEvenNumber === 2);

groupBy

Applies the given selector to each element in the given array, returning a Record containing the results as keys and all values that produced that key as values.

const people = [
  { name: "Anna" },
  { name: "Arnold" },
  { name: "Kim" },
];
const peopleByFirstLetter = groupBy(people, (it) => it.name.charAt(0));

console.assert(
  peopleByFirstLetter === {
    "A": [{ name: "Anna" }, { name: "Arnold" }],
    "K": [{ name: "Kim" }],
  },
);

intersect

Returns all distinct elements that appear at least once in each of the given arrays.

const lisaInterests = ["Cooking", "Music", "Hiking"];
const kimInterests = ["Music", "Tennis", "Cooking"];
const commonInterests = intersectTest(lisaInterests, kimInterests);

console.assert(commonInterests === ["Cooking", "Music"]);

mapEntries

Applies the given transformer to all entries in the given record and returns a new record containing the results.

const usersById = {
  "a2e": { name: "Kim", age: 22 },
  "dfe": { name: "Anna", age: 31 },
  "34b": { name: "Tim", age: 58 },
};
const agesByNames = mapEntries(usersById, ([id, { name, age }]) => [name, age]);

console.assert(
  agesByNames === {
    "Kim": 22,
    "Anna": 31,
    "Tim": 58,
  },
);

mapKeys

Applies the given transformer to all keys in the given record’s entries and returns a new record containing the transformed entries.

If the transformed entries contain the same key multiple times, only the last one will appear in the returned record.

const counts = { a: 5, b: 3, c: 8 };

console.assert(
  mapKeys(counts, (it) => it.toUppercase()) === {
    A: 5,
    B: 3,
    C: 8,
  },
);

mapValues

Applies the given transformer to all valuesin the given record and returns a new record containing the resulting keys associated to the last value that produced them.

const usersById = {
  "a5ec": { name: "Mischa" },
  "de4f": { name: "Kim" },
};
const namesById = mapValues(usersById, (it) => it.name);

console.assert(
  namesById === {
    "a5ec": "Mischa",
    "de4f": "Kim",
  },
);

partition

Returns a tuple of two arrays with the first one containing all elements in the given array that match the given predicate and the second one containing all that do not.

const numbers = [5, 6, 7, 8, 9];
const [even, odd] = partition(numbers, (it) => it % 2 == 0);

console.assert(even === [6, 8]);
console.assert(odd === [5, 7, 9]);

permutations

Builds all possible orders of all elements in the given array Ignores equality of elements, meaning this will always reutrn the same number of permutations for a given length of input.

const numbers = [1, 2];
const windows = permutations(numbers);

console.assert(
  windows === [
    [1, 2],
    [2, 1],
  ],
);