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std/collections/distinct_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.
/** * Returns all elements in the given array that produce a distinct value using * the given selector, preserving order by first occurrence. * * @example * ```ts * import { distinctBy } from "https://deno.land/std@$STD_VERSION/collections/distinct_by.ts"; * import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts"; * * const names = ["Anna", "Kim", "Arnold", "Kate"]; * const exampleNamesByFirstLetter = distinctBy(names, (it) => it.charAt(0)); * * assertEquals(exampleNamesByFirstLetter, ["Anna", "Kim"]); * ``` */export function distinctBy<T, D>( array: readonly T[], selector: (el: T) => D,): T[] { const selectedValues = new Set<D>(); const ret: T[] = [];
for (const element of array) { const currentSelectedValue = selector(element);
if (!selectedValues.has(currentSelectedValue)) { selectedValues.add(currentSelectedValue); ret.push(element); } }
return ret;}