# numelDimension
> Return the size (i.e., number of elements) of a specified dimension for a provided [ndarray][@stdlib/ndarray/ctor].
## 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
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`][@stdlib/ndarray/shape] when **only** a single dimension size is needed. For retrieving multiple dimension sizes, use [`@stdlib/ndarray/shape`][@stdlib/ndarray/shape] directly.
## Examples
```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
// 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 ) );
}
```
[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray/tree/main/ctor
[@stdlib/ndarray/shape]: https://github.com/stdlib-js/ndarray/tree/main/shape
[@stdlib/ndarray/array]: https://github.com/stdlib-js/ndarray/tree/main/array
[@stdlib/ndarray/numel]: https://github.com/stdlib-js/ndarray/tree/main/numel