d778ddb2c8
Fix typo to fit the context Fix typo add space Fix small typo Fix small typo Fix typo Fix typo Fix typo Fix typo Fix typo Fix typo Fix typo Update tail.md Fix typo Fix small typo Fix typo Fix typo Fix typo Fix typo Fix small typo Fix typo Fix small typo Fix typo Fix typo Fix typo Fix typo Fix typo Fix typo Fix typo Fix typo Fix typo
15 lines
603 B
Markdown
15 lines
603 B
Markdown
### groupBy
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Groups the elements of an array based on the given function.
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Use `Array.map()` to map the values of an array to a function or property name.
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Use `Array.reduce()` to create an object, where the keys are produced from the mapped results.
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```js
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const groupBy = (arr, func) =>
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arr.map(typeof func === 'function' ? func : val => val[func])
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.reduce((acc, val, i) => { acc[val] = (acc[val] || []).concat(arr[i]); return acc; }, {});
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// groupBy([6.1, 4.2, 6.3], Math.floor) -> {4: [4.2], 6: [6.1, 6.3]}
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// groupBy(['one', 'two', 'three'], 'length') -> {3: ['one', 'two'], 5: ['three']}
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```
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