### partition

Groups the elements into two arrays, depending on the provided function's truthiness for each element.

Use `Array.reduce()` to create an array of two arrays.
Use `Array.push()` to add elements for which `fn` returns `true` to the first array and elements for which `fn` returns `false` to the second one.

```js
const partition = (arr, fn) =>
  arr.reduce((acc, val, i, arr) => {acc[fn(val,i,arr) ? 0 :1].push(val); return acc;},[[],[]]);
```

```js
var users = [
  { 'user': 'barney',  'age': 36, 'active': false },
  { 'user': 'fred',    'age': 40, 'active': true }
];
partition(users, o => o.active) // [[{ 'user': 'fred',    'age': 40, 'active': true }],[{ 'user': 'barney',  'age': 36, 'active': false }]]
```