npm package: @stdlib/ndarray-sub2ind
Description: Convert subscripts to a linear index.
Author: The Stdlib Authors
Latest version: 0.2.3

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# sub2ind

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> Convert subscripts to a linear index.

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/ndarray-sub2ind
```

</section>

<section class="usage">

## Usage

```javascript
var sub2ind = require( '@stdlib/ndarray-sub2ind' );
```

#### sub2ind( shape, ...subscripts\[, options] )

Converts subscripts to a linear index.

```javascript
var shape = [ 2, 2 ];

var idx = sub2ind( shape, 1, 0 );
// returns 2
```

The function supports the following `options`:

-   **mode**: specifies how to handle subscripts which exceed array dimensions. The following modes are supported:

    -   `throw`: specifies that the function should throw an error when a subscript exceeds array dimensions.
    -   `normalize`: specifies that the function should normalize negative subscripts and throw an error when a subscript exceeds array dimensions.
    -   `wrap`: specifies that the function should wrap around subscripts exceeding array dimensions using modulo arithmetic.
    -   `clamp`: specifies that the function should set subscripts exceeding array dimensions to either `0` (minimum index) or the maximum index along a particular dimension.

    If provided a `mode` array, each array element corresponds to a dimension. If provided fewer modes than dimensions, the function reuses modes using modulo arithmetic. Default: `[ 'throw' ]`.

-   **order**: specifies whether an array is `row-major` (C-style) or `column-major` (Fortran-style). Default: `'row-major'`.

By default, the function assumes a row-major array. To return a linear index for a column-major array, set the `order` option.

```javascript
var shape = [ 2, 2 ];
var opts = {};

opts.order = 'column-major';
var idx = sub2ind( shape, 1, 0, opts );
// returns 1
```

By default, the function throws an `error` if provided subscripts which exceed array dimensions. To specify alternative behavior, set the `mode` option.

```javascript
var shape = [ 2, 2 ];
var opts = {};

opts.mode = 'wrap';
var idx = sub2ind( shape, -2, 0, opts );
// returns 0

opts.mode = 'clamp';
idx = sub2ind( shape, 10, 10, opts );
// returns 3
```

To specify separate modes for each dimension, provide a `mode` array.

```javascript
var shape = [ 2, 2, 2 ];
var opts = {
    'mode': [
        'wrap',
        'clamp'
    ]
};

var idx = sub2ind( shape, -2, 10, -1, opts );
// returns 3
```

</section>

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<section class="notes">

</section>

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<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var numel = require( '@stdlib/ndarray-base-numel' );
var sub2ind = require( '@stdlib/ndarray-sub2ind' );

var shape = [ 3, 3, 3 ];
var len = numel( shape );

var arr = [];
var i;
for ( i = 0; i < len; i++ ) {
    arr.push( i );
}

var opts = {
    'order': 'column-major'
};

console.log( '' );
console.log( 'Dimensions: %s.', shape.join( 'x' ) );
console.log( 'View:' );
console.log( '' );

var slice;
var idx;
var row;
var j;
var k;
for ( k = 0; k < shape[ 2 ]; k++ ) {
    slice = 'A[:,:,'+k+'] = ';
    console.log( slice );
    for ( i = 0; i < shape[ 0 ]; i++ ) {
        row = '  ';
        for ( j = 0; j < shape[ 1 ]; j++ ) {
            idx = sub2ind( shape, i, j, k, opts );
            row += arr[ idx ];
            if ( j < shape[ 1 ]-1 ) {
                row += ', ';
            }
        }
        console.log( row );
    }
    console.log( '' );
}
```

</section>

<!-- /.examples -->

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</section>

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<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/ndarray-array`][@stdlib/ndarray/array]</span><span class="delimiter">: </span><span class="description">multidimensional arrays.</span>
-   <span class="package-name">[`@stdlib/ndarray-ctor`][@stdlib/ndarray/ctor]</span><span class="delimiter">: </span><span class="description">multidimensional array constructor.</span>
-   <span class="package-name">[`@stdlib/ndarray-ind2sub`][@stdlib/ndarray/ind2sub]</span><span class="delimiter">: </span><span class="description">convert a linear index to an array of subscripts.</span>

</section>

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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].

#### Community

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---

## License

See [LICENSE][stdlib-license].


## Copyright

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

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[@stdlib/ndarray/ctor]: https://www.npmjs.com/package/@stdlib/ndarray-ctor

[@stdlib/ndarray/ind2sub]: https://www.npmjs.com/package/@stdlib/ndarray-ind2sub

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