28 lines
782 B
Markdown
28 lines
782 B
Markdown
---
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title: Array difference based on function
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tags: array
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expertise: intermediate
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cover: blog_images/folded-map.jpg
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firstSeen: 2017-12-19T12:32:24+02:00
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lastUpdated: 2020-10-22T20:23:47+03:00
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---
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Filters out all values from an array for which the comparator function does not return `true`.
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- Use `Array.prototype.filter()` and `Array.prototype.findIndex()` to find the appropriate values.
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- Omit the last argument, `comp`, to use a default strict equality comparator.
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```js
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const differenceWith = (arr, val, comp = (a, b) => a === b) =>
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arr.filter(a => val.findIndex(b => comp(a, b)) === -1);
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```
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```js
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differenceWith(
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[1, 1.2, 1.5, 3, 0],
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[1.9, 3, 0],
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(a, b) => Math.round(a) === Math.round(b)
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); // [1, 1.2]
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differenceWith([1, 1.2, 1.3], [1, 1.3, 1.5]); // [1.2]
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```
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