https://github.com/stdlib-js/utils-group
Group values as arrays associated with distinct keys.
https://github.com/stdlib-js/utils-group
aggregate array collection group group-by groupby javascript node node-js nodejs partition split stdlib summarize typed-array util utilities utility utils
Last synced: about 1 month ago
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Group values as arrays associated with distinct keys.
- Host: GitHub
- URL: https://github.com/stdlib-js/utils-group
- Owner: stdlib-js
- License: apache-2.0
- Created: 2021-06-14T16:41:26.000Z (over 4 years ago)
- Default Branch: main
- Last Pushed: 2025-03-10T00:25:56.000Z (9 months ago)
- Last Synced: 2025-04-12T17:44:36.912Z (8 months ago)
- Topics: aggregate, array, collection, group, group-by, groupby, javascript, node, node-js, nodejs, partition, split, stdlib, summarize, typed-array, util, utilities, utility, utils
- Language: JavaScript
- Homepage: https://github.com/stdlib-js/stdlib
- Size: 1.25 MB
- Stars: 1
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
- Citation: CITATION.cff
- Security: SECURITY.md
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README
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# group
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
> Group values as arrays associated with distinct keys.
## Installation
```bash
npm install @stdlib/utils-group
```
Alternatively,
- To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).
- If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).
- For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).
The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.
To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.
## Usage
```javascript
var group = require( '@stdlib/utils-group' );
```
#### group( collection, \[options,] groups )
Groups values as arrays associated with distinct keys.
```javascript
var arr = [ 'beep', 'boop', 'foo', 'bar' ];
var groups = [ 'b', 'b', 'f', 'b' ];
var out = group( arr, groups );
// returns { 'b': [ 'beep', 'boop', 'bar' ], 'f': [ 'foo' ] }
```
The function accepts the following `options`:
- **returns**: specifies the output format. If the option equals `'values'`, the function outputs element values. If the option equals `'indices'`, the function outputs element indices. If the option equals `'*'`, the function outputs both element indices and values. Default: `'values'`.
By default, the function returns element values. To return element indices, set the `returns` option to `'indices'`.
```javascript
var arr = [ 'beep', 'boop', 'foo', 'bar' ];
var groups = [ 'b', 'b', 'f', 'b' ];
var opts = {
'returns': 'indices'
};
var out = group( arr, opts, groups );
// returns { 'b': [ 0, 1, 3 ], 'f': [ 2 ] }
```
To return index-element pairs, set the `returns` option to `'*'`.
```javascript
var arr = [ 'beep', 'boop', 'foo', 'bar' ];
var groups = [ 'b', 'b', 'f', 'b' ];
var opts = {
'returns': '*'
};
var out = group( arr, opts, groups );
// returns { 'b': [ [ 0, 'beep' ], [ 1, 'boop' ], [ 3, 'bar' ] ], 'f': [ [ 2, 'foo' ] ] }
```
## Notes
- Both `collection` and `groups` **must** be collections. A collection may be either an [`Array`][mdn-array], [`Typed Array`][mdn-typed-array], or an array-like [`Object`][mdn-object] (excluding `strings` and `functions`).
- Each value in `groups` should resolve to a value which can be serialized as an `object` key. As a counterexample,
```javascript
var arr = [ 'beep', 'boop', 'foo', 'bar' ];
var groups = [ {}, {}, {}, {} ];
var out = group( arr, groups );
// returns { '[object Object]': [ 'beep', 'boop', 'foo', 'bar' ] }
```
while each "group" is unique, all collection elements resolve to the same group because each group identifier serializes to the same `string`.
## Examples
```javascript
var randu = require( '@stdlib/random-base-randu' );
var floor = require( '@stdlib/math-base-special-floor' );
var group = require( '@stdlib/utils-group' );
var vals;
var arr;
var out;
var g;
var i;
var j;
vals = [ 'beep', 'boop', 'foo', 'bar', 'woot', 'woot' ];
// Generate a random collection...
arr = new Array( 100 );
for ( i = 0; i < arr.length; i++ ) {
j = floor( randu()*vals.length );
arr[ i ] = vals[ j ];
}
// Randomly assign collection values to groups...
g = new Array( arr.length );
for ( i = 0; i < arr.length; i++ ) {
g[ i ] = floor( randu()*vals.length );
}
// Compute the groups:
out = group( arr, g );
console.log( out );
```
* * *
## See Also
- [`@stdlib/utils-bifurcate`][@stdlib/utils/bifurcate]: split values into two groups.
- [`@stdlib/utils-count-by`][@stdlib/utils/count-by]: group values according to an indicator function and return group counts.
- [`@stdlib/utils-group-by`][@stdlib/utils/group-by]: group values according to an indicator function.
* * *
## Notice
This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].
#### Community
[![Chat][chat-image]][chat-url]
---
## License
See [LICENSE][stdlib-license].
## Copyright
Copyright © 2016-2025. The Stdlib [Authors][stdlib-authors].
[npm-image]: http://img.shields.io/npm/v/@stdlib/utils-group.svg
[npm-url]: https://npmjs.org/package/@stdlib/utils-group
[test-image]: https://github.com/stdlib-js/utils-group/actions/workflows/test.yml/badge.svg?branch=main
[test-url]: https://github.com/stdlib-js/utils-group/actions/workflows/test.yml?query=branch:main
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/utils-group/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/utils-group?branch=main
[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg
[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im
[stdlib]: https://github.com/stdlib-js/stdlib
[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
[deno-url]: https://github.com/stdlib-js/utils-group/tree/deno
[deno-readme]: https://github.com/stdlib-js/utils-group/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/utils-group/tree/umd
[umd-readme]: https://github.com/stdlib-js/utils-group/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/utils-group/tree/esm
[esm-readme]: https://github.com/stdlib-js/utils-group/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/utils-group/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/utils-group/main/LICENSE
[mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
[mdn-object]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object
[@stdlib/utils/bifurcate]: https://github.com/stdlib-js/utils-bifurcate
[@stdlib/utils/count-by]: https://github.com/stdlib-js/utils-count-by
[@stdlib/utils/group-by]: https://github.com/stdlib-js/utils-group-by