---
title: unzipWith
tags: array,function,advanced
---

Creates an array of elements, ungrouping the elements in an array produced by [zip](#zip) and applying the provided function.

- Use `Math.max.apply()` to get the longest subarray in the array, `Array.prototype.map()` to make each element an array.
- Use `Array.prototype.reduce()` and `Array.prototype.forEach()` to map grouped values to individual arrays.
- Use `Array.prototype.map()` and the spread operator (`...`) to apply `fn` to each individual group of elements.

```js
const unzipWith = (arr, fn) =>
  arr
    .reduce(
      (acc, val) => (val.forEach((v, i) => acc[i].push(v)), acc),
      Array.from({
        length: Math.max(...arr.map(x => x.length))
      }).map(x => [])
    )
    .map(val => fn(...val));
```

```js
unzipWith([[1, 10, 100], [2, 20, 200]], (...args) => args.reduce((acc, v) => acc + v, 0)); // [3, 30, 300]
```