30-seconds-of-code/snippets/js/s/function-based-reversed-array-unique-values.md

title, type, language, tags, cover, dateModified

title	type	language	tags	cover	dateModified
Reversed unique values in array based on function	snippet	javascript	array	beach-from-above	2021-10-13T19:29:39+02:00

Finds all unique values of an array, based on a provided comparator function, starting from the right.

• Use Array.prototype.reduceRight() and Array.prototype.some() to create an array containing only the last unique occurrence of each value, based on the comparator function, fn.
• The comparator function takes two arguments: the values of the two elements being compared.

const uniqueElementsByRight = (arr, fn) =>
  arr.reduceRight((acc, v) => {
    if (!acc.some(x => fn(v, x))) acc.push(v);
    return acc;
  }, []);

uniqueElementsByRight(
  [
    { id: 0, value: 'a' },
    { id: 1, value: 'b' },
    { id: 2, value: 'c' },
    { id: 1, value: 'd' },
    { id: 0, value: 'e' }
  ],
  (a, b) => a.id == b.id
); // [ { id: 0, value: 'e' }, { id: 1, value: 'd' }, { id: 2, value: 'c' } ]