30 lines
1021 B
Markdown
30 lines
1021 B
Markdown
---
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title: Invert object
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type: snippet
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tags: [object]
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cover: pineapple-on-green
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dateModified: 2020-10-20T23:02:01+03:00
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---
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Inverts the key-value pairs of an object, without mutating it.
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- Use `Object.keys()` and `Array.prototype.reduce()` to invert the key-value pairs of an object and apply the function provided (if any).
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- Omit the second argument, `fn`, to get the inverted keys without applying a function to them.
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- The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.
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```js
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const invertKeyValues = (obj, fn) =>
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Object.keys(obj).reduce((acc, key) => {
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const val = fn ? fn(obj[key]) : obj[key];
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acc[val] = acc[val] || [];
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acc[val].push(key);
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return acc;
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}, {});
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```
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```js
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invertKeyValues({ a: 1, b: 2, c: 1 }); // { 1: [ 'a', 'c' ], 2: [ 'b' ] }
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invertKeyValues({ a: 1, b: 2, c: 1 }, value => 'group' + value);
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// { group1: [ 'a', 'c' ], group2: [ 'b' ] }
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```
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