@stdlib/utils-group NPM

group

Group values as arrays associated with distinct keys.

Installation

npm install @stdlib/utils-group

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 );

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.