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.
The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.
When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.
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!
Convert subscripts to a linear index.
import sub2ind from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-base-sub2ind@esm/index.mjs';Converts subscripts to a linear index.
var shape = [ 2, 2 ];
var strides = [ 2, 1 ];
var offset = 0;
var mode = [ 'throw' ];
var idx = sub2ind( shape, strides, offset, 1, 0, mode );
// returns 2The function supports the following modes:
- 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.
var shape = [ 2, 2 ];
var strides = [ 2, 1 ];
var offset = 0;
var mode = [ 'wrap' ];
var idx = sub2ind( shape, strides, offset, -2, 0, mode );
// returns 0
mode = [ 'clamp' ];
idx = sub2ind( shape, strides, offset, 10, 10, mode );
// returns 3-
When provided fewer
modesthan dimensions, the function recyclesmodesusing modulo arithmetic.var shape = [ 2, 2, 2 ]; var strides = [ 4, 2, 1 ]; var offset = 0; var mode = [ 'wrap', 'clamp' ]; var idx = sub2ind( shape, strides, offset, -2, 10, -1, mode ); // returns 3
-
When provided a stride array containing negative strides, if an
offsetis greater than0, the function treats subscripts as mapping to a linear index in an underlying data buffer for the array, thus returning a linear index from the perspective of that buffer. If anoffsetis equal to0, the function treats subscripts as mapping to a linear index in an array view, thus returning a linear index from the perspective of that view.Dims: 2x2 Buffer: [ 1, 2, 3, 4 ] View = [ a00, a01, a10, a11 ] Strides: 2,1 Offset: 0 View = [ 1, 2, 3, 4 ] Strides: 2,-1 Offset: 1 View = [ 2, 1, 4, 3 ] Strides: -2,1 Offset: 2 View = [ 3, 4, 1, 2 ] Strides: -2,-1 Offset: 3 View = [ 4, 3, 2, 1 ]var shape = [ 2, 2 ]; var strides = [ -2, 1 ]; var offset = 2; var mode = [ 'throw' ]; // From the perspective of a view... var idx = sub2ind( shape, strides, 0, 0, 0, mode ); // returns 0 idx = sub2ind( shape, strides, 0, 0, 1, mode ); // returns 1 idx = sub2ind( shape, strides, 0, 1, 0, mode ); // returns 2 idx = sub2ind( shape, strides, 0, 1, 1, mode ); // returns 3 // From the perspective of an underlying buffer... idx = sub2ind( shape, strides, offset, 0, 0, mode ); // returns 2 idx = sub2ind( shape, strides, offset, 0, 1, mode ); // returns 3 idx = sub2ind( shape, strides, offset, 1, 0, mode ); // returns 0 idx = sub2ind( shape, strides, offset, 1, 1, mode ); // returns 1
In short, from the perspective of a view, view data is always ordered.
<!DOCTYPE html>
<html lang="en">
<body>
<script type="module">
import discreteUniform from 'https://cdn.jsdelivr.net/gh/stdlib-js/random-base-discrete-uniform@esm/index.mjs';
import shape2strides from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-base-shape2strides@esm/index.mjs';
import strides2offset from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-base-strides2offset@esm/index.mjs';
import numel from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-base-numel@esm/index.mjs';
import randu from 'https://cdn.jsdelivr.net/gh/stdlib-js/random-base-randu@esm/index.mjs';
import sub2ind from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-base-sub2ind@esm/index.mjs';
var shape = [ 3, 3 ];
var strides = shape2strides( shape, 'row-major' );
var mode = [ 'throw' ];
var len = numel( shape );
var arr = [];
var i;
for ( i = 0; i < len; i++ ) {
arr.push( i );
}
var offset;
var idx;
var row;
var j;
var n;
var m;
for ( i = 0; i < 20; i++ ) {
j = discreteUniform( 0, shape.length-1 );
strides[ j ] = ( randu() < 0.5 ) ? -1 : 1;
offset = strides2offset( shape, strides );
console.log( '' );
console.log( 'Dimensions: %s.', shape.join( 'x' ) );
console.log( 'Strides: %s.', strides.join( ',' ) );
console.log( 'View:' );
for ( n = 0; n < shape[ 0 ]; n++ ) {
row = ' ';
for ( m = 0; m < shape[ 1 ]; m++ ) {
idx = sub2ind( shape, strides, offset, n, m, mode );
row += arr[ idx ];
if ( m < shape[ 1 ]-1 ) {
row += ', ';
}
}
console.log( row );
}
}
</script>
</body>
</html>This package is part of stdlib, a standard library 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.
See LICENSE.
Copyright © 2016-2025. The Stdlib Authors.