numelDimension

Return the size (i.e., number of elements) of a specified dimension for a provided ndarray.

Usage

var numelDimension = require( '@stdlib/ndarray/numel-dimension' );

numelDimension( x, dim )

Returns the size (i.e., number of elements) of a specified dimension for a provided ndarray.

var zeros = require( '@stdlib/ndarray/zeros' );

var x = zeros( [ 4, 2, 3 ] );
// returns <ndarray>

var d = numelDimension( x, 0 );
// returns 4

The function accepts the following arguments:

x: input ndarray.
dim: dimension index. If provided an integer less than zero, the dimension index is resolved relative to the last dimension, with the last dimension corresponding to the value -1.

Notes

This function is intended as a slight performance optimization over @stdlib/ndarray/shape when only a single dimension size is needed. For retrieving multiple dimension sizes, use @stdlib/ndarray/shape directly.

Examples

var zeros = require( '@stdlib/ndarray/zeros' );
var slice = require( '@stdlib/ndarray/slice' );
var E = require( '@stdlib/slice/multi' );
var S = require( '@stdlib/slice/ctor' );
var numelDimension = require( '@stdlib/ndarray/numel-dimension' );

// Create an array:
var x = zeros( [ 10, 10, 10, 10 ] );
// returns <ndarray>

// Define some slices:
var slices = [
    // :,:,:,:
    E( null, null, null, null ),

    // 5:10,4,2:4,::-1
    E( S( 5, 10 ), 4, S( 2, 4 ), S( null, null, -1 ) ),

    // :,:,2,:
    E( null, null, 2, null ),

    // 1,2,3,:
    E( 1, 2, 3, null ),

    // 1,3,::2,4::2
    E( 1, 3, S( null, null, 2 ), S( 4, null, 2 ) )
];

// Resolve the size of the first dimension for each slice...
var s;
var i;
for ( i = 0; i < slices.length; i++ ) {
    s = slice( x, slices[ i ] );
    console.log( '(%s) => %d', s.shape.join( ',' ), numelDimension( s, 0 ) );
}