31 lines
719 B
Markdown
31 lines
719 B
Markdown
---
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title: Index array based on function
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type: snippet
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language: javascript
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tags: [array,object]
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author: chalarangelo
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cover: guitar-living-room
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dateModified: 2021-06-20T05:00:00-04:00
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---
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Creates an object from an array, using a function to map each value to a key.
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- Use `Array.prototype.reduce()` to create an object from `arr`.
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- Apply `fn` to each value of `arr` to produce a key and add the key-value pair to the object.
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```js
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const indexBy = (arr, fn) =>
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arr.reduce((obj, v, i) => {
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obj[fn(v, i, arr)] = v;
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return obj;
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}, {});
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```
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```js
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indexBy([
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{ id: 10, name: 'apple' },
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{ id: 20, name: 'orange' }
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], x => x.id);
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// { '10': { id: 10, name: 'apple' }, '20': { id: 20, name: 'orange' } }
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```
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