# toRotr90
> Return a new ndarray where a matrix (or a stack of matrices) is rotated 90 degrees clockwise.
## Usage
```javascript
var toRotr90 = require( '@stdlib/ndarray/base/to-rotr90' );
```
#### toRotr90( x, k )
Returns a new ndarray where a matrix (or a stack of matrices) is rotated 90 degrees clockwise.
```javascript
var array = require( '@stdlib/ndarray/array' );
var x = array( [ [ 1, 2 ], [ 3, 4 ] ] );
// returns [ [ 1, 2 ], [ 3, 4 ] ]
var y = toRotr90( x, 1 );
// returns [ [ 3, 1 ], [ 4, 2 ] ]
```
The function accepts the following arguments:
- **x**: input ndarray.
- **k**: number of times to rotate by 90 degrees. Positive values rotate clockwise. Negative values rotate counterclockwise.
## Notes
- If `k > 0`, the function rotates the matrix clockwise.
- If `k < 0`, the function rotates the matrix counterclockwise.
- If provided an ndarray with fewer than two dimensions, the function does not perform a rotation and simply returns a copy of the input ndarray.
## Examples
```javascript
var array = require( '@stdlib/ndarray/array' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var toRotr90 = require( '@stdlib/ndarray/base/to-rotr90' );
// Create a 2x3 matrix:
var x = array( [ [ 1, 2, 3 ], [ 4, 5, 6 ] ] );
// Rotate 90 degrees clockwise:
var y = toRotr90( x, 1 );
var arr = ndarray2array( y );
// returns [ [ 4, 1 ], [ 5, 2 ], [ 6, 3 ] ]
// Rotate 180 degrees:
y = toRotr90( x, 2 );
arr = ndarray2array( y );
// returns [ [ 6, 5, 4 ], [ 3, 2, 1 ] ]
// Rotate 270 degrees clockwise (equivalent to 90 degrees counterclockwise):
y = toRotr90( x, 3 );
arr = ndarray2array( y );
// returns [ [ 3, 6 ], [ 2, 5 ], [ 1, 4 ] ]
// Rotate 360 degrees (equivalent to no rotation):
y = toRotr90( x, 4 );
arr = ndarray2array( y );
// returns [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]
// Rotate 90 degrees counterclockwise (equivalent to 270 degrees clockwise):
y = toRotr90( x, -1 );
arr = ndarray2array( y );
// returns [ [ 3, 6 ], [ 2, 5 ], [ 1, 4 ] ]
```