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groupValuesOnKey

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

Installation

npm install @stdlib/array-base-group-values-on-key

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md 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

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.

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.

Notes

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

  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.

Examples

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 );

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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.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2025. The Stdlib Authors.