30-seconds-of-code/javascript/snippets/filter-unique.md

title, type, tags, cover, dateModified

title	type	tags	cover	dateModified
Filter unique array values	snippet	array	tulips-and-reeds	2020-11-02T19:41:00+02:00

Creates an array with the unique values filtered out.

• Use the Set constructor and the spread operator (...) to create an array of the unique values in arr.
• Use Array.prototype.filter() to create an array containing only the non-unique values.

const filterUnique = arr =>
  [...new Set(arr)].filter(i => arr.indexOf(i) !== arr.lastIndexOf(i));

filterUnique([1, 2, 2, 3, 4, 4, 5]); // [2, 4]