Travis build: 1368

README.md

@@ -142,6 +142,8 @@ average(1, 2, 3);
 * [`take`](#take)
 * [`takeRight`](#takeright)
 * [`union`](#union)
+* [`unionBy`](#unionby)
+* [`unionWith`](#unionwith)
 * [`uniqueElements`](#uniqueelements)
 * [`without`](#without)
 * [`zip`](#zip)
@@ -1892,6 +1894,56 @@ union([1, 2, 3], [4, 3, 2]); // [1,2,3,4]
 <br>[⬆ Back to top](#table-of-contents)
 
 
+### unionBy
+
+Returns every element that exists in any of the two arrays once, after applying the provided function to each array element of both.
+
+Create a `Set` by applying all `fn` to all values of `a`.
+Create a `Set` from `a` and all elements in `b` whose value, after applying `fn` does not match a value in the previously created set.
+Return the last set converted to an array.
+
+```js
+const unionBy = (a, b, fn) => {
+  const s = new Set(a.map(v => fn(v)));
+  return Array.from(new Set([...a, ...b.filter(x => !s.has(fn(x)))]));
+};
+```
+
+<details>
+<summary>Examples</summary>
+
+```js
+unionBy([2.1], [1.2, 2.3], Math.floor); // [2.1, 1.2]
+```
+
+</details>
+
+<br>[⬆ Back to top](#table-of-contents)
+
+
+### unionWith
+
+Returns every element that exists in any of the two arrays once, using a provided comparator function.
+
+Create a `Set` with all values of `a` and values in `b` for which the comparator finds no matches in `a`, using `Array.findIndex()`.
+
+```js
+const unionWith = (a, b, comp) =>
+  Array.from(new Set([...a, ...b.filter(x => a.findIndex(y => comp(x, y)) === -1)]));
+```
+
+<details>
+<summary>Examples</summary>
+
+```js
+unionWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0, 3.9], (a, b) => Math.round(a) === Math.round(b)); // [1, 1.2, 1.5, 3, 0, 3.9]
+```
+
+</details>
+
+<br>[⬆ Back to top](#table-of-contents)
+
+
 ### uniqueElements
 
 Returns all unique values of an array.

snippets/unionWith.md

@@ -6,9 +6,7 @@ Create a `Set` with all values of `a` and values in `b` for which the comparator
 
 ```js
 const unionWith = (a, b, comp) =>
-  Array.from(
+  Array.from(new Set([...a, ...b.filter(x => a.findIndex(y => comp(x, y)) === -1)]));
-    new Set([...a, ...b.filter(x => a.findIndex(y => comp(x, y)) === -1)])
-  );
 ```
 
 ```js