30-seconds-of-code/snippets/unionWith.md

title, tags, expertise, cover, firstSeen, lastUpdated

title	tags	expertise	cover	firstSeen	lastUpdated
Array union based on function	array	intermediate	blog_images/orange-coffee-4.jpg	2018-01-24T12:19:41+02:00	2020-10-22T20:24:44+03:00

Returns every element that exists in any of the two arrays at least once, using a provided comparator function.

• Create a Set with all values of a and values in b for which the comparator finds no matches in a, using Array.prototype.findIndex().

const unionWith = (a, b, comp) =>
  Array.from(
    new Set([...a, ...b.filter(x => a.findIndex(y => comp(x, y)) === -1)])
  );

unionWith(
  [1, 1.2, 1.5, 3, 0],
  [1.9, 3, 0, 3.9],
  (a, b) => Math.round(a) === Math.round(b)
);
// [1, 1.2, 1.5, 3, 0, 3.9]