19 lines
572 B
Markdown
19 lines
572 B
Markdown
---
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title: intersectionBy
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tags: array,function,intermediate
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---
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Returns a list of elements that exist in both arrays, after applying the provided function to each array element of both.
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Create a `Set` by applying `fn` to all elements in `b`, then use `Array.prototype.filter()` on `a` to only keep elements, which produce values contained in `b` when `fn` is applied to them.
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```js
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const intersectionBy = (a, b, fn) => {
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const s = new Set(b.map(fn));
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return a.filter(x => s.has(fn(x)));
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};
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```
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```js
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intersectionBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [2.1]
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``` |