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group

Group values as arrays associated with distinct keys.

Installation

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 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 group = require( '@stdlib/utils-group' );

group( collection, [options,] groups )

Groups values as arrays associated with distinct keys.

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'.

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 '*'.

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, Typed Array, or an array-like 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,

  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

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 );

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See Also

• @stdlib/utils-bifurcate: split values into two groups.
• @stdlib/utils-count-by: group values according to an indicator function and return group counts.
• @stdlib/utils-group-by: group values according to an indicator function.

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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 © 2016-2024. The Stdlib Authors.