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ind2sub

Convert a linear index to an array of subscripts.

Installation

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 available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md 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

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

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

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( '' );
    }
}

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See Also

• @stdlib/ndarray-array: multidimensional arrays.
• @stdlib/ndarray-ctor: multidimensional array constructor.
• @stdlib/ndarray-sub2ind: convert subscripts to a linear index.

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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 © 2016-2024. The Stdlib Authors.