35 lines
992 B
Markdown
35 lines
992 B
Markdown
---
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title: Unique values in array based on function
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tags: array
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expertise: intermediate
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cover: blog_images/sunrise-over-mountains.jpg
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firstSeen: 2018-07-18T20:49:07+03:00
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lastUpdated: 2021-10-13T19:29:39+02:00
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---
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Finds all unique values of an array, based on a provided comparator function.
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- Use `Array.prototype.reduce()` and `Array.prototype.some()` to create an array containing only the first unique occurrence of each value, based on the comparator function, `fn`.
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- The comparator function takes two arguments: the values of the two elements being compared.
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```js
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const uniqueElementsBy = (arr, fn) =>
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arr.reduce((acc, v) => {
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if (!acc.some(x => fn(v, x))) acc.push(v);
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return acc;
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}, []);
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```
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```js
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uniqueElementsBy(
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[
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{ id: 0, value: 'a' },
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{ id: 1, value: 'b' },
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{ id: 2, value: 'c' },
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{ id: 1, value: 'd' },
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{ id: 0, value: 'e' }
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],
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(a, b) => a.id == b.id
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); // [ { id: 0, value: 'a' }, { id: 1, value: 'b' }, { id: 2, value: 'c' } ]
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```
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