18 lines
572 B
Markdown
18 lines
572 B
Markdown
---
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title: unionWith
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tags: array,function,intermediate
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---
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Returns every element that exists in any of the two arrays once, using a provided comparator function.
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- Create a `Set` with all values of `a` and values in `b` for which the comparator finds no matches in `a`, using `Array.prototype.findIndex()`.
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```js
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const unionWith = (a, b, comp) =>
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Array.from(new Set([...a, ...b.filter(x => a.findIndex(y => comp(x, y)) === -1)]));
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```
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```js
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unionWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0, 3.9], (a, b) => Math.round(a) === Math.round(b)); // [1, 1.2, 1.5, 3, 0, 3.9]
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```
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