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@stdlib/ndarray-base-ind2sub - 0.2.2 | npmpackage.info

@stdlib/ndarray-base-ind2sub

Convert a linear index to an array of subscripts.

0.2.2

Apache-2.0

JavaScript

59.69 kB

4.3

Installations

npm install @stdlib/ndarray-base-ind2sub

Developer Guide

BETA

Typescript

Yes

Module System

CommonJS

Min. Node Version

>=0.10.0

Node Version

16.20.2

NPM Version

8.19.4 Pull Requests

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0

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0

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0

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Unable to fetch releases

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JavaScript

JavaScript (61.28%)

C (38.72%)

Developer

stdlib-js

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GitHub Statistics

Apache-2.0 License

5 Stars

65 Commits

3 Watchers

5 Branches

14 Contributors

Updated on May 26, 2025

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https://opencollective.com/stdlib

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View All 14 Contributors

Package Meta Information

Latest Version

0.2.2

Package Id

@stdlib/ndarray-base-ind2sub@0.2.2

Unpacked Size

59.69 kB

Size

13.54 kB

File Count

NPM Version

8.19.4

Node Version

16.20.2

Published on

Jul 28, 2024

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Dependencies

@stdlib/array-base-zeros @stdlib/math-base-special-trunc @stdlib/ndarray-index-modes @stdlib/ndarray-orders @stdlib/string-format @stdlib/utils-define-nonenumerable-read-only-property @stdlib/error-tools-fmtprodmsg

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!

ind2sub

Convert a linear index to an array of subscripts.

Installation

1npm install @stdlib/ndarray-base-ind2sub

Usage

1var ind2sub = require( '@stdlib/ndarray-base-ind2sub' );

ind2sub( shape, strides, offset, order, idx, mode )

Converts a linear index to an array of subscripts.

1var shape = [ 2, 2 ];
2var order = 'row-major';
3var strides = [ 2, 1 ];
4var offset = 0;
5
6var subscripts = ind2sub( shape, strides, offset, order, 1, 'throw' );
7// returns [ 0, 1 ]

The function supports the following modes:

throw: specifies that the function should throw an error when a linear index exceeds array dimensions.
normalize: specifies that the function should normalize negative 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.

1var shape = [ 2, 2 ];
2var order = 'row-major';
3var strides = [ 2, 1 ];
4var offset = 0;
5
6var idx = ind2sub( shape, strides, offset, order, -2, 'wrap' );
7// returns [ 1, 0 ]
8
9idx = ind2sub( shape, strides, offset, order, 10, 'clamp' );
10// returns [ 1, 1 ]

The order parameter specifies whether an array is row-major (C-style) or column-major (Fortran-style).

1var shape = [ 2, 2 ];
2var order = 'column-major';
3var strides = [ 1, 2 ];
4var offset = 0;
5
6var idx = ind2sub( shape, strides, offset, order, 2, 'throw' );
7// returns [ 0, 1 ]

ind2sub.assign( shape, strides, offset, order, idx, mode, out )

Converts a linear index to an array of subscripts and assigns results to a provided output array.

1var shape = [ 2, 2 ];
2var order = 'row-major';
3var strides = [ 2, 1 ];
4var offset = 0;
5
6var out = [ 0, 0 ];
7var subscripts = ind2sub.assign( shape, strides, offset, order, 1, 'throw', out );
8// returns [ 0, 1 ]
9
10var bool = ( subscripts === out );
11// returns true

Notes

When provided a stride array containing negative strides, if an offset is greater than 0, the function interprets the linear index as an index into the underlying data buffer for the array, thus returning subscripts from the perspective of that buffer. If an offset is equal to 0, the function treats the linear index as an index into an array view, thus returning subscripts from the perspective of that view.

1Dims: 2x2
2Buffer: [ 1, 2, 3, 4 ]
3
4View = [ a00, a01,
5         a10, a11 ]
6
7Strides: 2,1
8Offset: 0
9
10View = [ 1, 2,
11         3, 4 ]
12
13Strides: 2,-1
14Offset: 1
15
16View = [ 2, 1,
17         4, 3 ]
18
19Strides: -2,1
20Offset: 2
21
22View = [ 3, 4,
23         1, 2 ]
24
25Strides: -2,-1
26Offset: 3
27
28View = [ 4, 3,
29         2, 1 ]

1var shape = [ 2, 2 ];
2var order = 'row-major';
3var strides = [ -2, 1 ];
4var offset = 2;
5var mode = 'throw';
6
7// From the perspective of a view...
8var s = ind2sub( shape, strides, 0, order, 0, mode );
9// returns [ 0, 0 ]
10
11s = ind2sub( shape, strides, 0, order, 1, mode );
12// returns [ 0, 1 ]
13
14s = ind2sub( shape, strides, 0, order, 2, mode );
15// returns [ 1, 0 ]
16
17s = ind2sub( shape, strides, 0, order, 3, mode );
18// returns [ 1, 1 ]
19
20// From the perspective of an underlying buffer...
21s = ind2sub( shape, strides, offset, order, 0, mode );
22// returns [ 1, 0 ]
23
24s = ind2sub( shape, strides, offset, order, 1, mode );
25// returns [ 1, 1 ]
26
27s = ind2sub( shape, strides, offset, order, 2, mode );
28// returns [ 0, 0 ]
29
30s = ind2sub( shape, strides, offset, order, 3, mode );
31// returns [ 0, 1 ]

In short, from the perspective of a view, view data is always ordered.

Examples

1var discreteUniform = require( '@stdlib/random-base-discrete-uniform' );
2var shape2strides = require( '@stdlib/ndarray-base-shape2strides' );
3var strides2offset = require( '@stdlib/ndarray-base-strides2offset' );
4var numel = require( '@stdlib/ndarray-base-numel' );
5var randu = require( '@stdlib/random-base-randu' );
6var abs = require( '@stdlib/math-base-special-abs' );
7var ind2sub = require( '@stdlib/ndarray-base-ind2sub' );
8
9// Specify array characteristics:
10var shape = [ 3, 3, 3 ];
11var order = 'row-major';
12
13// Compute array meta data:
14var ndims = shape.length;
15var strides = shape2strides( shape, order );
16var len = numel( shape );
17
18// Determine stride indices to be used for formatting how views are displayed...
19var s0;
20var s1;
21if ( order === 'column-major' ) {
22    s0 = ndims - 1;
23    s1 = s0 - 1;
24} else { // row-major
25    s0 = 0;
26    s1 = s0 + 1;
27}
28
29// Initialize a linear array...
30var arr = [];
31var i;
32for ( i = 0; i < len; i++ ) {
33    arr.push( 0 );
34}
35
36// Generate random views and display the mapping of elements in the linear array to view subscripts...
37var offset;
38var row;
39var j;
40var s;
41for ( i = 0; i < 20; i++ ) {
42    // Randomly flip the sign of one of the strides...
43    j = discreteUniform( 0, ndims-1 );
44    strides[ j ] *= ( randu() < 0.5 ) ? -1 : 1;
45    offset = strides2offset( shape, strides );
46
47    // Print view meta data...
48    console.log( '' );
49    console.log( 'Dimensions: %s.', shape.join( 'x' ) );
50    console.log( 'Strides: %s.', strides.join( ',' ) );
51    console.log( 'View (subscripts):' );
52
53    // Print the mapping of elements in the linear array to view subscripts...
54    row = '  ';
55    for ( j = 0; j < len; j++ ) {
56        s = ind2sub( shape, strides, offset, order, j, 'throw' );
57        row += '(' + s.join( ',' ) + ')';
58        if ( ndims === 1 && j === len-1 ) {
59            console.log( row );
60        } else if ( ndims === 2 && (j+1)%abs( strides[ s0 ] ) === 0 ) {
61            console.log( row );
62            row = '  ';
63        } else if ( ndims > 2 && (j+1)%abs( strides[ s1 ] ) === 0 ) {
64            console.log( row );
65            if ( (j+1)%abs( strides[ s0 ] ) === 0 ) {
66                console.log( '' );
67            }
68            row = '  ';
69        } else {
70            row += ', ';
71        }
72    }
73}

C APIs

Usage

1#include "stdlib/ndarray/base/ind2sub.h"

stdlib_ndarray_ind2sub( ndims, shape, strides, offset, order, idx, mode, *out )

Computes the minimum and maximum linear indices in an underlying data buffer accessible to an array view.

1#include "stdlib/ndarray/index_modes.h"
2#include "stdlib/ndarray/orders.h"
3#include <stdint.h>
4
5int64_t ndims = 2;
6int64_t shape[] = { 3, 3 };
7int64_t strides[] = { -3, 1 };
8int64_t offset = 6;
9
10int64_t out[ 2 ];
11
12int8_t status = stdlib_ndarray_ind2sub( ndims, shape, strides, offset, STDLIB_NDARRAY_ROW_MAJOR, 7, STDLIB_NDARRAY_INDEX_ERROR, out );
13if ( status == -1 ) {
14    // Handle error...
15}

The function accepts the following arguments:

ndims: [in] int64_t number of dimensions.
shape: [in] int64_t* array shape (dimensions).
strides: [in] int64_t* array strides.
offset: [in] int64_t index offset.
order: [in] enum STDLIB_NDARRAY_ORDER specifies whether an array is row-major (C-style) or column-major (Fortran-style).
idx: [in] int64_t linear index in an array view.
mode: [in] enum STDLIB_NDARRAY_INDEX_MODE specifies how to handle a linear index which exceeds array dimensions.
out: [out] int64_t* output array.

1int8_t stdlib_ndarray_ind2sub( const int64_t ndims, const int64_t *shape, const int64_t *strides, const int64_t offset, const enum STDLIB_NDARRAY_ORDER order, const int64_t idx, const enum STDLIB_NDARRAY_INDEX_MODE mode, int64_t *out );

Examples

1#include "stdlib/ndarray/base/ind2sub.h"
2#include "stdlib/ndarray/index_modes.h"
3#include "stdlib/ndarray/orders.h"
4#include <stdint.h>
5#include <stdio.h>
6#include <inttypes.h>
7
8int main( void ) {
9    int64_t ndims = 2;
10    int64_t shape[] = { 3, 3 };
11    int64_t strides[] = { -3, 1 };
12    int64_t offset = 6;
13
14    int64_t out[ 2 ];
15
16    stdlib_ndarray_ind2sub( ndims, shape, strides, offset, STDLIB_NDARRAY_ROW_MAJOR, 7, STDLIB_NDARRAY_INDEX_ERROR, out );
17
18    int i;
19    printf( "subscripts = { " );
20    for ( i = 0; i < ndims; i++ ) {
21        printf( "%"PRId64"", out[ i ] );
22        if ( i < ndims-1 ) {
23            printf( ", " );
24        }
25    }
26    printf( " }\n" );
27}

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.

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License

See LICENSE.

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Score

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Last Scanned on 2025-06-30

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Learn More

@stdlib/ndarray-base-ind2sub

Installations

Developer Guide

Yes

CommonJS

>=0.10.0

16.20.2

8.19.4

Pull Requests

0

0

0

Issues

0

0

0

Releases

Unable to fetch releases

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Developer

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Dependencies

ind2sub

Installation

Usage

ind2sub( shape, strides, offset, order, idx, mode )

ind2sub.assign( shape, strides, offset, order, idx, mode, out )

Notes

Examples

C APIs

Usage

stdlib_ndarray_ind2sub( ndims, *shape, *strides, offset, order, idx, mode, *out )

Examples

Notice

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10

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3

1

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4.3

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stdlib_ndarray_ind2sub( ndims, shape, strides, offset, order, idx, mode, *out )