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


npm install @stdlib/ndarray-numel-dimension


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.


  • 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.


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


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.






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  • stdlib-bot
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