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

title, tags, expertise, cover, firstSeen, lastUpdated

title	tags	expertise	cover	firstSeen	lastUpdated
Filter non-unique array values	array	beginner	blog_images/digital-nomad-10.jpg	2017-12-17T17:55:51+02:00	2020-11-02T19:40:45+02:00

Creates an array with the non-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 unique values.

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

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