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# spreadDimensions

> Expand the shape of an array to a specified dimensionality by spreading its dimensions to specified dimension indices and inserting dimensions of size one for the remaining dimensions.

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## Usage

```javascript
var spreadDimensions = require( '@stdlib/ndarray/base/spread-dimensions' );
```

#### spreadDimensions( ndims, x, dims, writable )

Expands the shape of an array to a specified dimensionality by spreading its dimensions to specified dimension indices and inserting dimensions of size one for the remaining dimensions.

```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 <ndarray>[ [ 1, 2 ], [ 3, 4 ] ]

// Prepend a singleton dimension:
var y = spreadDimensions( 3, x, [ 1, 2 ], false );
// returns <ndarray>[ [ [ 1, 2 ], [ 3, 4 ] ] ]

var sh = getShape( y );
// returns [ 1, 2, 2 ]

// Append a singleton dimension:
y = spreadDimensions( 3, x, [ 0, 1 ], false );
// returns <ndarray>[ [ [ 1 ], [ 2 ] ], [ [ 3 ], [ 4 ] ] ]

sh = getShape( y );
// returns [ 2, 2, 1 ]

// Insert a singleton dimension:
y = spreadDimensions( 3, x, [ 0, 2 ], false );
// returns <ndarray>[ [ [ 1, 2 ] ], [ [ 3, 4 ] ] ]

sh = getShape( y );
// returns [ 2, 1, 2 ]
```

The function accepts the following arguments:

-   **ndims**: number of dimensions in the output ndarray. Must be greater than or equal to the number of dimensions in the input ndarray.
-   **x**: input ndarray.
-   **dims**: dimension indices specifying where to place the dimensions of the input ndarray. Must resolve to normalized indices arranged in ascending order.
-   **writable**: boolean indicating whether a returned ndarray should be writable.

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## Notes

-   Each provided dimension index must reside on the interval `[-ndims, ndims-1]`. If provided a negative dimension index, the position at which to place a respective dimension is computed as `ndims + index`.
-   Provided dimension indices must resolve to normalized dimension indices arranged in ascending order.
-   The `writable` parameter **only** applies to ndarray constructors supporting **read-only** instances.

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## Examples

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

```javascript
var array = require( '@stdlib/ndarray/array' );
var getShape = require( '@stdlib/ndarray/shape' );
var numel = require( '@stdlib/ndarray/base/numel' );
var ind2sub = require( '@stdlib/ndarray/ind2sub' );
var spreadDimensions = require( '@stdlib/ndarray/base/spread-dimensions' );

// Create a 2-dimensional array:
var x = array( [ [ 1, 2 ], [ 3, 4 ] ], {
    'order': 'column-major'
});
// returns <ndarray>

// Spread dimensions:
var y = spreadDimensions( 5, x, [ 1, 3 ], false );
// returns <ndarray>

// Retrieve the shape:
var sh = getShape( y );
// returns [ 1, 2, 1, 2, 1 ]

// Retrieve the number of elements:
var N = numel( sh );

// Loop through the array elements...
var i;
for ( i = 0; i < N; i++ ) {
    console.log( 'Y[%s] = %d', ind2sub( sh, i ).join( ', ' ), y.iget( i ) );
}
```

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