npm package: @stdlib/array-base-group-indices
Description: Group element indices as arrays associated with distinct keys.
Author: The Stdlib Authors
Latest version: 0.2.4

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# groupIndices

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

> Group element indices as arrays associated with distinct keys.

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/array-base-group-indices
```

</section>

<section class="usage">

## Usage

```javascript
var groupIndices = require( '@stdlib/array-base-group-indices' );
```

#### groupIndices( x, groups )

Groups element indices as arrays associated with distinct keys.

```javascript
var x = [ 'beep', 'boop', 'foo', 'bar' ];
var groups = [ 'b', 'b', 'f', 'b' ];

var out = groupIndices( x, groups );
// returns { 'b': [ 0, 1, 3 ], 'f': [ 2 ] }
```

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## Notes

-   Each value in `groups` should resolve to a value which can be serialized as an object key. As a counterexample,

    ```javascript
    var x = [ 'beep', 'boop', 'foo', 'bar' ];
    var groups = [ {}, {}, {}, {} ];

    var out = groupIndices( x, groups );
    // returns { '[object Object]': [ 0, 1, 2, 3 ] }
    ```

    while each "group" is unique, all input array elements resolve to the same group because each group identifier serializes to the same string.

</section>

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<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var take = require( '@stdlib/array-base-take-indexed' );
var groupIndices = require( '@stdlib/array-base-group-indices' );

// Define an initial array of values:
var values = [ 'beep', 'boop', 'foo', 'bar', 'woot', 'woot' ];

// Sample from the initial array to generate a random collection:
var indices = discreteUniform( 100, 0, values.length-1, {
    'dtype': 'generic'
});
var x = take( values, indices );
// returns [...]

// Randomly assign collection values to groups:
var groups = discreteUniform( x.length, 0, values.length, {
    'dtype': 'generic'
});

// Group the values:
var out = groupIndices( x, groups );
// returns {...}

console.log( out );
```

</section>

<!-- /.examples -->

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* * *

## 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

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---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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