23 lines
539 B
Markdown
23 lines
539 B
Markdown
---
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title: Deep flatten array
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tags: array,recursion
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cover: digital-nomad-4
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firstSeen: 2017-12-17T17:55:51+02:00
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lastUpdated: 2020-10-22T20:23:47+03:00
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---
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Deep flattens an array.
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- Use recursion.
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- Use `Array.prototype.concat()` with an empty array (`[]`) and the spread operator (`...`) to flatten an array.
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- Recursively flatten each element that is an array.
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```js
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const deepFlatten = arr =>
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[].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));
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```
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```js
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deepFlatten([1, [2], [[3], 4], 5]); // [1, 2, 3, 4, 5]
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```
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