# expandDimensions
> Expand the shape of an array by inserting a new dimension of size one at a specified dimension index.
## Usage
```javascript
var expandDimensions = require( '@stdlib/ndarray/base/expand-dimensions' );
```
#### expandDimensions( x, dim, writable )
Expands the shape of an array `x` by inserting a new dimension of size one at a specified dimension index.
```javascript
var getShape = require( '@stdlib/ndarray/shape' );
var array = require( '@stdlib/ndarray/array' );
// Create a 2x2 ndarray:
var x = array( [ [ 1, 2 ], [ 3, 4 ] ] );
// returns [ [ 1, 2 ], [ 3, 4 ] ]
// Prepend a singleton dimension:
var y = expandDimensions( x, 0, false );
// returns [ [ [ 1, 2 ], [ 3, 4 ] ] ]
var sh = getShape( y );
// returns [ 1, 2, 2 ]
// Append a singleton dimension:
y = expandDimensions( x, 2, false );
// returns [ [ [ 1 ], [ 2 ] ], [ [ 3 ], [ 4 ] ] ]
sh = getShape( y );
// returns [ 2, 2, 1 ]
// Insert a singleton dimension:
y = expandDimensions( x, 1, false );
// returns [ [ [ 1, 2 ] ], [ [ 3, 4 ] ] ]
sh = getShape( y );
// returns [ 2, 1, 2 ]
```
The function accepts the following arguments:
- **x**: input ndarray.
- **dim**: dimension index at which to insert a singleton dimension.
- **writable**: boolean indicating whether a returned ndarray should be writable.
## Notes
- A provided dimension index must reside on the interval `[-N-1, N]`, where `N` is the rank (i.e., number of dimensions) of the provided input array. If provided a negative dimension index, the position at which to insert a singleton dimension is computed as `N + dim + 1`. Hence, if provided `-1`, the resolved position is `N` (i.e., a singleton dimension is appended to the input array).
- The `writable` parameter **only** applies to ndarray constructors supporting **read-only** instances.
## Examples
```javascript
var uniform = require( '@stdlib/random/uniform' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var expandDimensions = require( '@stdlib/ndarray/base/expand-dimensions' );
var x = uniform( [ 3, 3, 3 ], -10.0, 10.0 );
console.log( ndarray2array( x ) );
var y = expandDimensions( x, 1, false );
console.log( ndarray2array( y ) );
```