/
associate_by.ts
42 lines (38 loc) · 1.21 KB
/
associate_by.ts
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// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
/**
* Transforms the given array into a Record, extracting the key of each element using the given selector.
* If the selector produces the same key for multiple elements, the latest one will be used (overriding the
* ones before it).
*
* Example:
*
* ```ts
* import { associateBy } from "https://deno.land/std@$STD_VERSION/collections/associate_by.ts"
* import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts";
*
* const users = [
* { id: 'a2e', userName: 'Anna' },
* { id: '5f8', userName: 'Arnold' },
* { id: 'd2c', userName: 'Kim' },
* ]
* const usersById = associateBy(users, it => it.id)
*
* assertEquals(usersById, {
* 'a2e': { id: 'a2e', userName: 'Anna' },
* '5f8': { id: '5f8', userName: 'Arnold' },
* 'd2c': { id: 'd2c', userName: 'Kim' },
* })
* ```
*/
export function associateBy<T>(
array: readonly T[],
selector: (el: T) => string,
): Record<string, T> {
const ret: Record<string, T> = {};
for (const element of array) {
const selectedValue = selector(element);
ret[selectedValue] = element;
}
return ret;
}