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About stdlib...

We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

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To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

ind2sub

NPM version Build Status Coverage Status

Convert a linear index to an array of subscripts.

Usage

To use in Observable,

ind2sub = require( 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-ind2sub@umd/browser.js' )

To vendor stdlib functionality and avoid installing dependency trees for Node.js, you can use the UMD server build:

var ind2sub = require( 'path/to/vendor/umd/ndarray-ind2sub/index.js' )

To include the bundle in a webpage,

<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-ind2sub@umd/browser.js"></script>

If no recognized module system is present, access bundle contents via the global scope:

<script type="text/javascript">
(function () {
    window.ind2sub;
})();
</script>

ind2sub( shape, idx[, options] )

Converts a linear index to an array of subscripts.

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.

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.

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.

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

<!DOCTYPE html>
<html lang="en">
<body>
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-base-numel@umd/browser.js"></script>
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-ind2sub@umd/browser.js"></script>
<script type="text/javascript">
(function () {

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( '' );
    }
}

})();
</script>
</body>
</html>

See Also

Notice

This package is part of 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, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2025. The Stdlib Authors.