Returns all elements in the given array that produce a distinct value using the given selector, preserving order by first occurrence

Example:

import { distinctBy } from "https://deno.land/std@0.130.0/collections/mod.ts";
import { assertEquals } from "https://deno.land/std@0.130.0/testing/asserts.ts";

const names = [ 'Anna', 'Kim', 'Arnold', 'Kate' ]
const exampleNamesByFirstLetter = distinctBy(names, it => it.charAt(0))

assertEquals(exampleNamesByFirstLetter, [ 'Anna', 'Kim' ])