129 lines
3.2 KiB
Markdown
Executable file
129 lines
3.2 KiB
Markdown
Executable file
index-array-by
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==============
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[![NPM package][npm-img]][npm-url]
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[![Build Size][build-size-img]][build-size-url]
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[![NPM Downloads][npm-downloads-img]][npm-downloads-url]
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A utility function to index arrays by any criteria.
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`indexBy(list, keyAccessors, multiItem = true)`
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## Quick start
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```js
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import indexBy from 'index-array-by';
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```
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or using a *script* tag
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```html
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<script src="//unpkg.com/index-array-by"></script>
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```
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## Usage example
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Given an array
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```js
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const people = [
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{ name: 'Mary', surname: 'Jane', age: 28 },
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{ name: 'John', surname: 'Smith', age: 24 },
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{ name: 'John', surname: 'Doe', age: 32 }
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];
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```
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Use `indexBy` to index it by a given attribute (string type `keyAccessor`) or any other custom criteria (function type `keyAccessor`). You can also pass an array of `keyAccessors` to retrieve a nested object recursively indexed by the multiple keys.
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Use the third parameter (`multiItem`) to indicate whether each key should point to a single item (unadvised if the keys are not unique) or an array of multiple items (default behavior).
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```js
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indexBy(people, 'surname', false);
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// Result:
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{
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Doe: { name: 'John', age: 32 },
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Jane: { name: 'Mary', age: 28 },
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Smith: { name: 'John', age: 24 }
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}
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```
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```js
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indexBy(people, 'name', true);
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// Result:
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{
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Mary: [ { surname: 'Jane', age: 28 } ],
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John: [
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{ surname: 'Smith', age: 24 },
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{ surname: 'Doe', age: 32 }
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]
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}
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```
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```js
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indexBy(people, ({ name, surname }) => `${surname}, ${name}`, false);
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// Result:
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{
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'Jane, Mary': { name: 'Mary', surname: 'Jane', age: 28 },
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'Smith, John': { name: 'John', surname: 'Smith', age: 24 },
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'Doe, John': { name: 'John', surname: 'Doe', age: 32 }
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}
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```
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```js
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indexBy(people, ['name', 'surname'], false));
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// Result:
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{
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Mary: { Jane: { age: 28 }},
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John: { Smith: { age: 24 }, Doe: { age: 32 }}
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}
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```
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```js
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indexBy(people, ({ age }) => `${Math.floor(age / 10) * 10}s`, true);
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// Result:
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{
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'20s': [
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{ name: 'Mary', surname: 'Jane', age: 28 },
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{ name: 'John', surname: 'Smith', age: 24 },
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],
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'30s': [{ name: 'John', surname: 'Doe', age: 32 }]
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}
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```
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The `multiItem` parameter also accepts a transformation function with the method to reduce multiple items into a single one. In this case, it's keeping only the max age.
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```js
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indexBy(people, 'name', items => Math.max(...items.map(item => item.age)));
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// Result:
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{
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John: 32,
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Mary: 28
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}
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```
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A fourth optional parameter (`flattenKeys`) (default: `false`) allows you to receive a flat array structure instead of the default nested format, with each item formatted as `{ keys: [<ordered unique keys for the item>], vals: <single or multiple item> }`.
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```js
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indexBy(people, ['name', 'surname'], true, true));
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// Result:
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[
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{ keys: ['Mary', 'Jane'], vals: [{ age: 28 }] },
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{ keys: ['John', 'Smith'], vals: [{ age: 24 }] },
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{ keys: ['John', 'Doe'], vals: [{ age: 32 }] }
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]
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```
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[npm-img]: https://img.shields.io/npm/v/index-array-by
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[npm-url]: https://npmjs.org/package/index-array-by
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[build-size-img]: https://img.shields.io/bundlephobia/minzip/index-array-by
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[build-size-url]: https://bundlephobia.com/result?p=index-array-by
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[npm-downloads-img]: https://img.shields.io/npm/dt/index-array-by
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[npm-downloads-url]: https://www.npmtrends.com/index-array-by
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