26 lines
720 B
Markdown
26 lines
720 B
Markdown
---
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title: intersectionBy
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tags: array,intermediate
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---
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Returns the 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`.
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- 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 [...new Set(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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intersectionBy(
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[{ title: 'Apple' }, { title: 'Orange' }],
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[{ title: 'Orange' }, { title: 'Melon' }],
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x => x.title
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); // [{ title: 'Orange' }]
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```
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