23 lines
509 B
Markdown
23 lines
509 B
Markdown
---
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title: frequencies
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tags: array,intermediate
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---
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Returns an object with the unique values of an array as keys and their frequencies as the values.
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Use `Array.prototype.reduce()` to map unique values to an object's keys, adding to existing keys every time the same value is encountered.
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```js
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const frequencies = arr =>
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arr.reduce(
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(a, v) => {
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a[v] = a[v] ? a[v] + 1 : 1;
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return a;
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}, {}
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);
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```
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```js
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frequencies(['a', 'b', 'a', 'c', 'a', 'a', 'b']); // { a: 4, b: 2, c: 1 }
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```
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