26 lines
700 B
Markdown
26 lines
700 B
Markdown
---
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title: flatten
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tags: array,recursion,intermediate
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---
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Flattens an array up to the specified depth.
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- Use recursion, decrementing `depth` by `1` for each level of depth.
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- Use `Array.prototype.reduce()` and `Array.prototype.concat()` to merge elements or arrays.
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- Base case, for `depth` equal to `1` stops recursion.
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- Omit the second argument, `depth`, to flatten only to a depth of `1` (single flatten).
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```js
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const flatten = (arr, depth = 1) =>
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arr.reduce(
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(a, v) =>
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a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v),
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[]
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);
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```
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```js
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flatten([1, [2], 3, 4]); // [1, 2, 3, 4]
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flatten([1, [2, [3, [4, 5], 6], 7], 8], 2); // [1, 2, 3, [4, 5], 6, 7, 8]
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```
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