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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"; * * type Person = { *   name: string; * }; * * const people: Person[] = [ *     { 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;}