@stdlib/utils-bifurcate-by NPM

bifurcateBy

Split values into two groups according to a predicate function.

Installation

npm install @stdlib/utils-bifurcate-by

Usage

var bifurcateBy = require( '@stdlib/utils-bifurcate-by' );

bifurcateBy( collection, [options,] predicate )

Splits values into two groups according to a predicate function, which specifies which group an element in the input collection belongs to. If a predicate function returns a truthy value, a collection element belongs to the first group; otherwise, a collection element belongs to the second group.

function predicate( v ) {
    return v[ 0 ] === 'b';
}
var arr = [ 'beep', 'boop', 'foo', 'bar' ];

var out = bifurcateBy( arr, predicate );
// returns [ [ 'beep', 'boop', 'bar' ], [ 'foo' ] ]

A predicate function is provided two arguments:

value: collection element
index: collection index

function predicate( v, i ) {
    console.log( '%d: %s', i, v );
    return v[ 0 ] === 'b';
}
var arr = [ 'beep', 'boop', 'foo', 'bar' ];

var out = bifurcateBy( arr, predicate );
// returns [ [ 'beep', 'boop', 'bar' ], [ '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'.
thisArg: execution context.

By default, the function returns element values. To return element indices, set the returns option to 'indices'.

function predicate( v ) {
    return v[ 0 ] === 'b';
}
var arr = [ 'beep', 'boop', 'foo', 'bar' ];

var opts = {
    'returns': 'indices'
};
var out = bifurcateBy( arr, opts, predicate );
// returns [ [ 0, 1, 3 ], [ 2 ] ]

To return index-element pairs, set the returns option to '*'.

function predicate( v ) {
    return v[ 0 ] === 'b';
}
var arr = [ 'beep', 'boop', 'foo', 'bar' ];

var opts = {
    'returns': '*'
};
var out = bifurcateBy( arr, opts, predicate );
// returns [ [ [ 0, 'beep' ], [ 1, 'boop' ], [ 3, 'bar' ] ], [ [ 2, 'foo' ] ] ]

To set the predicate execution context, provide a thisArg.

function predicate( v ) {
    this.count += 1;
    return v[ 0 ] === 'b';
}
var context = {
    'count': 0
};
var opts = {
    'thisArg': context
};
var arr = [ 'beep', 'boop', 'foo', 'bar' ];

var out = bifurcateBy( arr, opts, predicate );
// returns [ [ 'beep', 'boop', 'bar' ], [ 'foo' ] ]

console.log( context.count );
// => 4

Notes

A collection may be either an Array, Typed Array, or an array-like Object (excluding strings and functions).

Examples

var randu = require( '@stdlib/random-base-randu' );
var floor = require( '@stdlib/math-base-special-floor' );
var bifurcateBy = require( '@stdlib/utils-bifurcate-by' );

var vals;
var arr;
var out;
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 ];
}

function predicate( v ) {
    return v[ 0 ] === 'b';
}

// Compute the groups:
out = bifurcateBy( arr, predicate );
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.