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sub2ind

Convert subscripts to a linear index.

Installation

npm install @stdlib/ndarray-sub2ind

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

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

Converts subscripts to a linear index.

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.

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.

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.

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

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

Examples

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( '' );
}

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See Also

• @stdlib/ndarray-array: multidimensional arrays.
• @stdlib/ndarray-ctor: multidimensional array constructor.
• @stdlib/ndarray-ind2sub: convert a linear index to an array of subscripts.

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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.