npm package: @stdlib/ndarray-ind2sub
Description: Convert a linear index to an array of subscripts.
Author: The Stdlib Authors
Latest version: 0.2.3

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# ind2sub

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> Convert a linear index to an array of subscripts.

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/ndarray-ind2sub
```

</section>

<section class="usage">

## Usage

```javascript
var ind2sub = require( '@stdlib/ndarray-ind2sub' );
```

#### ind2sub( shape, idx\[, options] )

Converts a linear index to an array of subscripts.

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

var s = ind2sub( shape, 2 );
// returns [ 1, 0 ]
```

The function supports the following `options`:

-   **mode**: specifies how to handle a linear index which exceeds array dimensions. The following modes are supported:

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

-   **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 subscripts for a column-major array, set the `order` option.

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

opts.order = 'column-major';
var s = ind2sub( shape, 1, opts );
// returns [ 1, 0 ]
```

By default, the function throws an `error` if provided a linear index which exceeds array dimensions. To specify alternative behavior, set the `mode` option.

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

opts.mode = 'wrap';
var s = ind2sub( shape, -5, opts );
// returns [ 1, 1 ]

opts.mode = 'clamp';
s = ind2sub( shape, 7, opts );
// returns [ 1, 1 ]
```

#### ind2sub.assign( shape, idx\[, options], out )

Converts a linear index to an array of subscripts and assigns results to a provided output array.

```javascript
var shape = [ 2, 2 ];
var out = [ 0, 0 ];

var subscripts = ind2sub.assign( shape, 1, out );
// returns [ 0, 1 ]

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

The function accepts the same `options` as above.

</section>

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</section>

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<section class="examples">

## Examples

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

```javascript
var numel = require( '@stdlib/ndarray-base-numel' );
var ind2sub = require( '@stdlib/ndarray-ind2sub' );

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 (subscripts):' );
console.log( '' );

var row;
var s;

row = '  ';
for ( i = 0; i < len; i++ ) {
    s = ind2sub( shape, i, opts );
    row += '(' + s.join( ',' ) + ')';
    if ( (i+1)%shape[0] === 0 ) {
        console.log( row );
        row = '  ';
    } else {
        row += ', ';
    }
    if ( (i+1)%(shape[0]*shape[1]) === 0 ) {
        console.log( '' );
    }
}
```

</section>

<!-- /.examples -->

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* * *

## 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-sub2ind`][@stdlib/ndarray/sub2ind]</span><span class="delimiter">: </span><span class="description">convert subscripts to a linear index.</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/array]: https://www.npmjs.com/package/@stdlib/ndarray-array

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

[@stdlib/ndarray/sub2ind]: https://www.npmjs.com/package/@stdlib/ndarray-sub2ind

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