8ee50178f3
Correct: `Array.from()` (it’s a static method) Incorrect: `Array.join()` (doesn’t exist; it’s a prototype method) This patch uses the common `#` syntax to denote `.prototype.`.
22 lines
911 B
Markdown
22 lines
911 B
Markdown
### invertKeyValues
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Inverts the key-value pairs of an object, without mutating it. 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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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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```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); // { group1: [ 'a', 'c' ], group2: [ 'b' ] }
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```
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