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https://github.com/stdlib-js/ndarray-ind2sub

Convert a linear index to an array of subscripts.
https://github.com/stdlib-js/ndarray-ind2sub

array idx ind2sub index javascript linear multidimensional ndarray node node-js nodejs shape stdlib sub2ind subscript types util utilities utility utils

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Convert a linear index to an array of subscripts.

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README 

        



  

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# ind2sub



[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] 



> Convert a linear index to an array of subscripts.



## Installation



```bash

npm install @stdlib/ndarray-ind2sub

```



Alternatively,



-   To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).

-   If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).

-   For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).



The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.



To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.



## 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.



## Examples



```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( '' );

    }

}

```



* * *



## See Also



-   [`@stdlib/ndarray-array`][@stdlib/ndarray/array]: multidimensional arrays.

-   [`@stdlib/ndarray-ctor`][@stdlib/ndarray/ctor]: multidimensional array constructor.

-   [`@stdlib/ndarray-sub2ind`][@stdlib/ndarray/sub2ind]: convert subscripts to a linear index.



* * *



## 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



[![Chat][chat-image]][chat-url]



---



## License



See [LICENSE][stdlib-license].



## Copyright



Copyright © 2016-2024. The Stdlib [Authors][stdlib-authors].



[npm-image]: http://img.shields.io/npm/v/@stdlib/ndarray-ind2sub.svg

[npm-url]: https://npmjs.org/package/@stdlib/ndarray-ind2sub



[test-image]: https://github.com/stdlib-js/ndarray-ind2sub/actions/workflows/test.yml/badge.svg?branch=main

[test-url]: https://github.com/stdlib-js/ndarray-ind2sub/actions/workflows/test.yml?query=branch:main



[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/ndarray-ind2sub/main.svg

[coverage-url]: https://codecov.io/github/stdlib-js/ndarray-ind2sub?branch=main



[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg

[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im



[stdlib]: https://github.com/stdlib-js/stdlib



[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors



[umd]: https://github.com/umdjs/umd

[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules



[deno-url]: https://github.com/stdlib-js/ndarray-ind2sub/tree/deno

[deno-readme]: https://github.com/stdlib-js/ndarray-ind2sub/blob/deno/README.md

[umd-url]: https://github.com/stdlib-js/ndarray-ind2sub/tree/umd

[umd-readme]: https://github.com/stdlib-js/ndarray-ind2sub/blob/umd/README.md

[esm-url]: https://github.com/stdlib-js/ndarray-ind2sub/tree/esm

[esm-readme]: https://github.com/stdlib-js/ndarray-ind2sub/blob/esm/README.md

[branches-url]: https://github.com/stdlib-js/ndarray-ind2sub/blob/main/branches.md



[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/ndarray-ind2sub/main/LICENSE



[@stdlib/ndarray/array]: https://github.com/stdlib-js/ndarray-array



[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray-ctor



[@stdlib/ndarray/sub2ind]: https://github.com/stdlib-js/ndarray-sub2ind