numelDimension

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

Installation

npm install @stdlib/ndarray-numel-dimension

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 ) );
}

See Also

• @stdlib/ndarray-array: multidimensional arrays.
• @stdlib/ndarray-ctor: multidimensional array constructor.
• @stdlib/ndarray-numel: return the number of elements in an ndarray.

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.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.