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.

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.
i: index of the first dimension.
j: index of the second dimension.
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 );