npm package: @stdlib/ndarray-numel-dimension
Description: Return the size (i.e., number of elements) of a specified dimension for a provided ndarray.
Author: The Stdlib Authors
Latest version: 0.2.3

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# numelDimension

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> Return the size (i.e., number of elements) of a specified dimension for a provided [ndarray][@stdlib/ndarray/ctor].

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/ndarray-numel-dimension
```

</section>

<section class="usage">

## Usage

```javascript
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][@stdlib/ndarray/ctor].

```javascript
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`.

</section>

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<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## Notes

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

</section>

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<!-- Package usage examples. -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

<!-- eslint-disable new-cap -->

```javascript
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 ) );
}
```

</section>

<!-- /.examples -->

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<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/ndarray-array`][@stdlib/ndarray/array]</span><span class="delimiter">: </span><span class="description">multidimensional arrays.</span>
-   <span class="package-name">[`@stdlib/ndarray-ctor`][@stdlib/ndarray/ctor]</span><span class="delimiter">: </span><span class="description">multidimensional array constructor.</span>
-   <span class="package-name">[`@stdlib/ndarray-numel`][@stdlib/ndarray/numel]</span><span class="delimiter">: </span><span class="description">return the number of elements in an ndarray.</span>

</section>

<!-- /.related -->

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<section class="main-repo" >

* * *

## Notice

This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].

#### Community

[![Chat][chat-image]][chat-url]

---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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[umd]: https://github.com/umdjs/umd
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[deno-url]: https://github.com/stdlib-js/ndarray-numel-dimension/tree/deno
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[@stdlib/ndarray/ctor]: https://www.npmjs.com/package/@stdlib/ndarray-ctor

[@stdlib/ndarray/shape]: https://www.npmjs.com/package/@stdlib/ndarray-shape

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[@stdlib/ndarray/array]: https://www.npmjs.com/package/@stdlib/ndarray-array

[@stdlib/ndarray/numel]: https://www.npmjs.com/package/@stdlib/ndarray-numel

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