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// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
import { Grouping, Selector } from "./types.ts";
/** * 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: * * ```typescript * 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' } ], * }) * ``` */export function groupBy<T>(  array: Array<T>,  selector: Selector<T, string>,): Grouping<T> {  const ret: { [key: string]: Array<T> } = {};
  for (const element of array) {    const key = selector(element);
    if (ret[key] === undefined) {      ret[key] = [element];
      continue;    }
    ret[key].push(element);  }
  return ret;}