@stdlib/utils-reduce2d NPM

reduce2d

Reduce the number of dimensions by one of a two-dimensional nested array by applying a function against an accumulator and each element along the innermost dimension and returning the accumulation results as a one-dimensional array.

Installation

npm install @stdlib/utils-reduce2d

Usage

var reduce2d = require( '@stdlib/utils-reduce2d' );

reduce2d( arr, initial, fcn[, thisArg] )

Reduces the number of dimensions by one of a two-dimensional nested array by applying a function against an accumulator and each element along the innermost dimension and returning the accumulation results as a one-dimensional array.

var naryFunction = require( '@stdlib/utils-nary-function' );
var add = require( '@stdlib/math-base-ops-add' );

var arr = [
    [ 1, 2, 3 ],
    [ 4, 5, 6 ]
];

var out = reduce2d( arr, [ 0, 0 ], naryFunction( add, 2 ) );
// returns [ 6, 15 ]

The applied function is provided the following arguments:

accumulator: accumulated value.
value: array element.
indices: current array element indices.
arr: input array.

To set the this context when invoking the input function, provide a thisArg.

var add = require( '@stdlib/math-base-ops-add' );

function fcn( acc, v ) {
    this.count += 1;
    return add( acc, v );
}

var arr = [
    [ 1, 2, 3 ],
    [ 4, 5, 6 ]
];

var ctx = {
    'count': 0
};

var out = reduce2d( arr, [ 0, 0 ], fcn, ctx );
// returns [ 6, 15 ]

var cnt = ctx.count;
// returns 6

Notes

The function requires an array-like object containing an initial value for the accumulator for each reduction. The number of initial values must equal the size of the outermost input array dimension.

Examples

var filledarrayBy = require( '@stdlib/array-filled-by' );
var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var naryFunction = require( '@stdlib/utils-nary-function' );
var add = require( '@stdlib/math-base-ops-add' );
var zeros = require( '@stdlib/array-base-zeros' );
var reduce2d = require( '@stdlib/utils-reduce2d' );

function fill( i ) {
    var rand = discreteUniform( -10*(i+1), 10*(i+1) );
    return filledarrayBy( 10, 'float64', rand );
}

// Create a nested array of arrays:
var x = filledarrayBy( 10, 'generic', fill );

// Create an explicit binary function:
var f = naryFunction( add, 2 );

// Compute the sums along the innermost dimension...
var y = reduce2d( x, zeros( x.length ), f );

console.log( 'x:' );
console.log( x );

console.log( 'y:' );
console.log( y );

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.