bcc05a9a6e
Updated all By snippets to have matching behavior, consistent argument naming and added countBy as per #100.
20 lines
607 B
Markdown
20 lines
607 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, fn) =>
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arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val, i) => {
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acc[val] = (acc[val] || []).concat(arr[i]);
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return acc;
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}, {});
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```
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```js
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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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