18 lines
723 B
Markdown
18 lines
723 B
Markdown
---
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title: bifurcateBy
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tags: array,intermediate
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---
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Splits values into two groups according to a predicate function, which specifies which group an element in the input collection belongs to. If the predicate function returns a truthy value, the collection element belongs to the first group; otherwise, it belongs to the second group.
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- Use `Array.prototype.reduce()` and `Array.prototype.push()` to add elements to groups, based on the value returned by `fn` for each element.
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```js
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const bifurcateBy = (arr, fn) =>
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arr.reduce((acc, val, i) => (acc[fn(val, i) ? 0 : 1].push(val), acc), [[], []]);
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```
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```js
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bifurcateBy(['beep', 'boop', 'foo', 'bar'], x => x[0] === 'b'); // [ ['beep', 'boop', 'bar'], ['foo'] ]
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```
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