24 lines
584 B
Markdown
24 lines
584 B
Markdown
---
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title: transform
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tags: object,array,intermediate
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---
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Applies a function against an accumulator and each key in the object (from left to right).
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- Use `Object.keys(obj)` to iterate over each key in the object, `Array.prototype.reduce()` to call the apply the specified function against the given accumulator.
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```js
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const transform = (obj, fn, acc) => Object.keys(obj).reduce((a, k) => fn(a, obj[k], k, obj), acc);
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```
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```js
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transform(
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{ a: 1, b: 2, c: 1 },
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(r, v, k) => {
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(r[v] || (r[v] = [])).push(k);
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return r;
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},
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{}
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); // { '1': ['a', 'c'], '2': ['b'] }
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```
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