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# toRotl90

> Return a new ndarray where a matrix (or a stack of matrices) is rotated 90 degrees counterclockwise.

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## Usage

```javascript
var toRotl90 = require( '@stdlib/ndarray/base/to-rotl90' );
```

#### toRotl90( x, k )

Returns a new ndarray where a matrix (or a stack of matrices) is rotated 90 degrees counterclockwise.

```javascript
var array = require( '@stdlib/ndarray/array' );

var x = array( [ [ 1, 2 ], [ 3, 4 ] ] );
// returns <ndarray>[ [ 1, 2 ], [ 3, 4 ] ]

var y = toRotl90( x, 1 );
// returns <ndarray>[ [ 2, 4 ], [ 1, 3 ] ]
```

The function accepts the following arguments:

-   **x**: input ndarray.
-   **k**: number of times to rotate by 90 degrees. Positive values rotate counterclockwise. Negative values rotate clockwise.

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## Notes

-   If `k > 0`, the function rotates the matrix counterclockwise.
-   If `k < 0`, the function rotates the matrix clockwise.
-   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.

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## Examples

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```javascript
var array = require( '@stdlib/ndarray/array' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var toRotl90 = require( '@stdlib/ndarray/base/to-rotl90' );

// Create a 2x3 matrix:
var x = array( [ [ 1, 2, 3 ], [ 4, 5, 6 ] ] );

// Rotate 90 degrees counterclockwise:
var y = toRotl90( x, 1 );
var arr = ndarray2array( y );
// returns [ [ 3, 6 ], [ 2, 5 ], [ 1, 4 ] ]

// Rotate 180 degrees:
y = toRotl90( x, 2 );
arr = ndarray2array( y );
// returns [ [ 6, 5, 4 ], [ 3, 2, 1 ] ]

// Rotate 270 degrees counterclockwise (equivalent to 90 degrees clockwise):
y = toRotl90( x, 3 );
arr = ndarray2array( y );
// returns [ [ 4, 1 ], [ 5, 2 ], [ 6, 3 ] ]

// Rotate 360 degrees (equivalent to no rotation):
y = toRotl90( x, 4 );
arr = ndarray2array( y );
// returns [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]

// Rotate 90 degrees clockwise (equivalent to k=3):
y = toRotl90( x, -1 );
arr = ndarray2array( y );
// returns [ [ 4, 1 ], [ 5, 2 ], [ 6, 3 ] ]
```

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