30-seconds-of-code/snippets/difference-with.md

title, tags, cover, firstSeen, lastUpdated

title	tags	cover	firstSeen	lastUpdated
Array difference based on function	array	folded-map	2017-12-19T12:32:24+02:00	2020-10-22T20:23:47+03:00

Filters out all values from an array for which the comparator function does not return true.

• Use Array.prototype.filter() and Array.prototype.findIndex() to find the appropriate values.
• Omit the last argument, comp, to use a default strict equality comparator.

const differenceWith = (arr, val, comp = (a, b) => a === b) =>
  arr.filter(a => val.findIndex(b => comp(a, b)) === -1);

differenceWith(
  [1, 1.2, 1.5, 3, 0],
  [1.9, 3, 0],
  (a, b) => Math.round(a) === Math.round(b)
); // [1, 1.2]
differenceWith([1, 1.2, 1.3], [1, 1.3, 1.5]); // [1.2]