# @stdlib/array-base-group-indices

0.2.2 • Public • Published

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# groupIndices

Group element indices as arrays associated with distinct keys.

## Installation

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

## Usage

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

#### groupIndices( x, groups )

Groups element indices as arrays associated with distinct keys.

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

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

## Notes

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

```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.

## Examples

```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 );```

## Notice

This package is part of 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, see the main project repository.

## Package Sidebar

### Install

`npm i @stdlib/array-base-group-indices`

### Repository

github.com/stdlib-js/array-base-group-indices

stdlib.io

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