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41 lines
1.2 KiB
Markdown
41 lines
1.2 KiB
Markdown
# flatMap
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Map each element of a nested array to a given iteratee function, then flatten it to the desired depth.
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It works the same as if you called [Array#flat](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat) with [Array#map](https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Global_Objects/Array/map) as `map(iteratee).flat(depth)` in the JavaScript language, but it's faster.
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## Signature
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```typescript
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function flatMap<T, U, D extends number = 1>(
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arr: T[],
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iteratee: (item: T) => U,
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depth?: D
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): Array<FlatArray<U[], D>>;
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```
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### Parameters
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- `arr` (`T[]`): The array to flatten.
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- `iteratee` (`T[]`): A function that maps each array element.
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- `depth` (`D`): The depth to flatten, which defaults to 1.
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### Returns
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(`Array<FlatArray<U[], D>>`): A new array with each element mapped and flattened to the desired depth.
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## Examples
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```typescript
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const array = [1, 2, 3];
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const result1 = flatMap(array, item => [item, item], 1);
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// Return [1, 1, 2, 2, 3, 3]
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const result2 = flatMap(array, item => [[item, item]], 2);
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// Return [1, 1, 2, 2, 3, 3]
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const result3 = flatMap(array, item => [[[item, item]]], 3);
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// Return [1, 1, 2, 2, 3, 3]
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```
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