25 lines
801 B
Markdown
25 lines
801 B
Markdown
---
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title: Check if all array elements are unique based on function
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tags: array
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expertise: intermediate
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author: maciv
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cover: blog_images/digital-nomad-10.jpg
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firstSeen: 2020-10-19T22:15:05+03:00
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lastUpdated: 2021-01-08T00:23:44+02:00
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---
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Checks if all elements in an array are unique, based on the provided mapping function.
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- Use `Array.prototype.map()` to apply `fn` to all elements in `arr`.
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- Create a new `Set` from the mapped values to keep only unique occurrences.
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- Use `Array.prototype.length` and `Set.prototype.size` to compare the length of the unique mapped values to the original array.
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```js
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const allUniqueBy = (arr, fn) => arr.length === new Set(arr.map(fn)).size;
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```
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```js
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allUniqueBy([1.2, 2.4, 2.9], Math.round); // true
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allUniqueBy([1.2, 2.3, 2.4], Math.round); // false
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```
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