30 lines
828 B
Markdown
30 lines
828 B
Markdown
---
|
|
title: Flatten array
|
|
tags: array,recursion
|
|
expertise: intermediate
|
|
cover: blog_images/green-plant.jpg
|
|
firstSeen: 2017-12-17T16:41:31+02:00
|
|
lastUpdated: 2020-10-22T20:23:47+03:00
|
|
---
|
|
|
|
Flattens an array up to the specified depth.
|
|
|
|
- Use recursion, decrementing `depth` by `1` for each level of depth.
|
|
- Use `Array.prototype.reduce()` and `Array.prototype.concat()` to merge elements or arrays.
|
|
- Base case, for `depth` equal to `1` stops recursion.
|
|
- Omit the second argument, `depth`, to flatten only to a depth of `1` (single flatten).
|
|
|
|
```js
|
|
const flatten = (arr, depth = 1) =>
|
|
arr.reduce(
|
|
(a, v) =>
|
|
a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v),
|
|
[]
|
|
);
|
|
```
|
|
|
|
```js
|
|
flatten([1, [2], 3, 4]); // [1, 2, 3, 4]
|
|
flatten([1, [2, [3, [4, 5], 6], 7], 8], 2); // [1, 2, 3, [4, 5], 6, 7, 8]
|
|
```
|