Yields r length Arrays from the input iterable. Order of selection is important and elements are chosen without replacement. If r is undefined, then the length of the iterable is used.

import { assertEquals } from "https://deno.land/std/testing/asserts.ts";
import { permutations } from "https://deno.land/x/combinatorics/mod.ts";

const sequences = [...permutations([1, 2, 3, 4], 2)];

assertEquals(sequences, [
  [1, 2], [1, 3], [1, 4],
  [2, 1], [2, 3], [2, 4],
  [3, 1], [3, 2], [3, 4],
  [4, 1], [4, 2], [4, 3],
]);