npm package: @stdlib/array-base-group-values-on-key
Description: Group the elements of an array according to a specified property name.
Author: The Stdlib Authors
Latest version: 0.1.1

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# groupValuesOnKey

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> Group the elements of an array according to a specified property name.

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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-values-on-key
```

</section>

<section class="usage">

## Usage

```javascript
var groupValuesOnKey = require( '@stdlib/array-base-group-values-on-key' );
```

#### groupValuesOnKey( x, key )

Groups the elements of an array according to a specified property name.

```javascript
var x = [
    {
        'x': 1,
        'y': 2
    },
    {
        'x': 1,
        'y': 3
    }
];

var out = groupValuesOnKey( x, 'y' );
// returns { '2': [ { 'x': 1, 'y': 2 } ], '3': [ { 'x': 1, 'y': 3 } ] }
```

The function supports the following parameters:

-   **x**: input array.
-   **key**: property name whose values are used to determine groups.

</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 associated with a specified `key` should resolve to a value which can be serialized as an object key. As a counterexample,

    ```javascript
    var x = [
        {
            'x': 1,
            'y': {}
        },
        {
            'x': 1,
            'y': {}
        }
    ];

    var out = groupValuesOnKey( x, 'y' );
    // returns { '[object Object]': [ { 'x': 1, 'y': {} }, { 'x': 1, 'y': {} } ] }
    ```

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

-   If provided an empty array, the function returns an empty object.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random-base-discrete-uniform' );
var filledBy = require( '@stdlib/array-base-filled-by' );
var groupValuesOnKey = require( '@stdlib/array-base-group-values-on-key' );

function clbk( idx ) {
    return {
        'x': idx,
        'y': discreteUniform( 0, 10 )
    };
}

// Create an array of random objects:
var values = filledBy( 100, clbk );

// Group elements according to the values of `y`:
var out = groupValuesOnKey( values, 'y' );
// 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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