add uniqueElements By and ByRight

snippets/uniqueElementsByRight.md

@@ -0,0 +1,27 @@
+### uniqueElementsByRight
+
+Returns all unique values of an array, based on a provided comparator function.
+
+Use `Array.reduce()` and `Array.some()` for an array containing only the last unique occurence of each value, based on the comparator function, `fn`.
+The comparator function takes two arguments: the values of the two elements being compared.
+
+```js
+const uniqueElementsByRight = (arr, fn) =>
+	arr.reduce((acc, v) => {
+		if (!acc.some(x => fn(v, x))) acc.push(v);
+		return acc;
+	}, []);
+```
+
+```js
+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' } ]
+```