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std/collections/group_by.ts

Deno standard library
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// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.// This module is browser compatible.
/** * 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. * * @example * ```ts * import { groupBy } from "https://deno.land/std@$STD_VERSION/collections/group_by.ts"; * import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts"; * * const people = [ * { name: "Anna" }, * { name: "Arnold" }, * { name: "Kim" }, * ]; * const peopleByFirstLetter = groupBy(people, (it) => it.name.charAt(0)); * * assertEquals( * peopleByFirstLetter, * { * "A": [{ name: "Anna" }, { name: "Arnold" }], * "K": [{ name: "Kim" }], * }, * ); * ``` */export function groupBy<T, K extends string>( array: readonly T[], selector: (el: T) => K,): Partial<Record<K, T[]>> { const ret: Partial<Record<K, T[]>> = {};
for (const element of array) { const key = selector(element); const arr = ret[key] ??= [] as T[]; arr.push(element); }
return ret;}