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

title, tags, expertise, author, firstSeen, lastUpdated

title	tags	expertise	author	firstSeen	lastUpdated
Check if all array elements are unique based on function	array	intermediate	maciv	2020-10-19T22:15:05+03:00	2021-01-08T00:23:44+02:00

Checks if all elements in an array are unique, based on the provided mapping function.

• Use Array.prototype.map() to apply fn to all elements in arr.
• Create a new Set from the mapped values to keep only unique occurrences.
• Use Array.prototype.length and Set.prototype.size to compare the length of the unique mapped values to the original array.

const allUniqueBy = (arr, fn) => arr.length === new Set(arr.map(fn)).size;

allUniqueBy([1.2, 2.4, 2.9], Math.round); // true
allUniqueBy([1.2, 2.3, 2.4], Math.round); // false