npm package: @stdlib/ndarray-base-expand-dimensions
Description: Expand the shape of an array by inserting a new dimension of size one at a specified axis.
Author: The Stdlib Authors
Latest version: 0.3.1

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# expandDimensions

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> Expand the shape of an array by inserting a new dimension of size one at a specified dimension index.

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/ndarray-base-expand-dimensions
```

</section>

<section class="usage">

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

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

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

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

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

// Insert a singleton dimension:
y = expandDimensions( x, 1, false );
// returns <ndarray>[ [ [ 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.

</section>

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<section class="notes">

## 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.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```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 ) );
```

</section>

<!-- /.examples -->

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* * *

## Notice

This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].

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---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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