npm package: @stdlib/ndarray-base-next-cartesian-index
Description: Return the next Cartesian index (i.e., set of subscripts/dimension indices).
Author: The Stdlib Authors
Latest version: 0.2.3

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# nextCartesianIndex

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> Return the next Cartesian index (i.e., set of subscripts/dimension indices).

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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-next-cartesian-index
```

</section>

<section class="usage">

## Usage

```javascript
var nextCartesianIndex = require( '@stdlib/ndarray-base-next-cartesian-index' );
```

#### nextCartesianIndex( shape, order, idx, dim )

Returns the next Cartesian index (i.e., set of subscripts/dimension indices).

```javascript
var idx = nextCartesianIndex( [ 2, 2, 2 ], 'row-major', [ 0, 0, 1 ], -1 );
// returns [ 0, 1, 0 ]
```

The function accepts the following arguments:

-   **shape**: array shape.
-   **order**: index iteration order. Must be either `row-major` (C-style) or `column-major` (Fortran-style).
-   **idx**: current dimension indices.
-   **dim**: index of the dimension from which to start incrementing (inclusive).

The `order` parameter specifies the index iteration order. When `order` is `row-major`, the last indices change fastest, and, when the `order` is `column-major`, the first indices change fastest.

```javascript
var idx = nextCartesianIndex( [ 2, 2, 2 ], 'column-major', [ 0, 1, 0 ], 0 );
// returns [ 1, 1, 0 ]
```

The `dim` parameter controls which dimensions are incremented. When `order` is `row-major`, if `dim` equals `shape.length-1` (or equivalently `-1`), the function increments over all dimensions from right-to-left (last-to-first). Similarly, when `order` is `column-major`, if `dim` equals `0`, the function increments over all dimensions from left-to-right (first-to-last). To restrict which dimensions can be incremented, set `dim` to a value other than the respective end. For example,

```javascript
// Increment starting from the second-to-last dimension:
var idx = nextCartesianIndex( [ 2, 2, 2 ], 'row-major', [ 0, 0, 0 ], -2 );
// returns [ 0, 1, 0 ]

idx = nextCartesianIndex( [ 2, 2, 2 ], 'row-major', idx, -2 );
// returns [ 1, 0, 0 ]

idx = nextCartesianIndex( [ 2, 2, 2 ], 'row-major', idx, -2 );
// returns [ 1, 1, 0 ]
```

#### nextCartesianIndex.assign( shape, order, idx, dim, out )

Returns the next Cartesian index (i.e., set of subscripts/dimension indices) and assigns results to a provided output array.

```javascript
var out = [ 0, 0, 0 ];
var idx = nextCartesianIndex.assign( [ 2, 2, 2 ], 'row-major', [ 0, 0, 1 ], -1, out );
// returns [ 0, 1, 0 ]

var bool = ( out === idx );
// returns true
```

The function accepts the following arguments:

-   **shape**: array shape.
-   **order**: index iteration order. Must be either `row-major` (C-style) or `column-major` (Fortran-style).
-   **idx**: current dimension indices.
-   **dim**: index of the dimension from which to start incrementing (inclusive).
-   **out**: output array.

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## Notes

-   The function does not check whether the current index is the "last" index. Instead, if the function is provided dimension indices corresponding to the last element, the function will cycle back to the "first" index.
-   If provided an empty shape (i.e., a shape corresponding to a zero-dimensional ndarray) or a dimension index `dim` which is out-of-bounds, the function returns `null`.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var array = require( '@stdlib/ndarray-array' );
var zeroTo = require( '@stdlib/array-base-zero-to' );
var nextCartesianIndex = require( '@stdlib/ndarray-base-next-cartesian-index' );

// Create an ndarray:
var x = array( zeroTo( 27 ), {
    'shape': [ 3, 3, 3 ]
});

// Initialize a set of indices:
var idx = [ 0, 0, 0 ];

// Iterate over each element in the array...
var i;
for ( i = 0; i < x.length; i++ ) {
    console.log( 'x[%s] = %d', idx.join( ',' ), x.get.apply( x, idx ) );
    idx = nextCartesianIndex.assign( x.shape, x.order, idx, -1, idx );
}
```

</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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