nextCartesianIndex

Return the next Cartesian index (i.e., set of subscripts/dimension indices).

Installation

npm install @stdlib/ndarray-base-next-cartesian-index

Usage

var nextCartesianIndex = require( '@stdlib/ndarray-base-next-cartesian-index' );

nextCartesianIndex( shape, order, idx, dim )

Returns the next Cartesian index (i.e., set of subscripts/dimension indices).

var idx = nextCartesianIndex( [ 2, 2, 2 ], 'row-major', [ 0, 0, 1 ], -1 );
// returns [ 0, 1, 0 ]

The function accepts the following arguments:

• shape: array shape.
• order: index iteration order. Must be either row-major (C-style) or column-major (Fortran-style).
• idx: current dimension indices.
• dim: index of the dimension from which to start incrementing (inclusive).

The order parameter specifies the index iteration order. When order is row-major, the last indices change fastest, and, when the order is column-major, the first indices change fastest.

var idx = nextCartesianIndex( [ 2, 2, 2 ], 'column-major', [ 0, 1, 0 ], 0 );
// returns [ 1, 1, 0 ]

The dim parameter controls which dimensions are incremented. When order is row-major, if dim equals shape.length-1 (or equivalently -1), the function increments over all dimensions from right-to-left (last-to-first). Similarly, when order is column-major, if dim equals 0, the function increments over all dimensions from left-to-right (first-to-last). To restrict which dimensions can be incremented, set dim to a value other than the respective end. For example,

// Increment starting from the second-to-last dimension:
var idx = nextCartesianIndex( [ 2, 2, 2 ], 'row-major', [ 0, 0, 0 ], -2 );
// returns [ 0, 1, 0 ]

idx = nextCartesianIndex( [ 2, 2, 2 ], 'row-major', idx, -2 );
// returns [ 1, 0, 0 ]

idx = nextCartesianIndex( [ 2, 2, 2 ], 'row-major', idx, -2 );
// returns [ 1, 1, 0 ]

nextCartesianIndex.assign( shape, order, idx, dim, out )

Returns the next Cartesian index (i.e., set of subscripts/dimension indices) and assigns results to a provided output array.

var out = [ 0, 0, 0 ];
var idx = nextCartesianIndex.assign( [ 2, 2, 2 ], 'row-major', [ 0, 0, 1 ], -1, out );
// returns [ 0, 1, 0 ]

var bool = ( out === idx );
// returns true

The function accepts the following arguments:

• shape: array shape.
• order: index iteration order. Must be either row-major (C-style) or column-major (Fortran-style).
• idx: current dimension indices.
• dim: index of the dimension from which to start incrementing (inclusive).
• out: output array.

Notes

• The function does not check whether the current index is the "last" index. Instead, if the function is provided dimension indices corresponding to the last element, the function will cycle back to the "first" index.
• If provided an empty shape (i.e., a shape corresponding to a zero-dimensional ndarray) or a dimension index dim which is out-of-bounds, the function returns null.

Examples

var array = require( '@stdlib/ndarray-array' );
var zeroTo = require( '@stdlib/array-base-zero-to' );
var nextCartesianIndex = require( '@stdlib/ndarray-base-next-cartesian-index' );

// Create an ndarray:
var x = array( zeroTo( 27 ), {
    'shape': [ 3, 3, 3 ]
});

// Initialize a set of indices:
var idx = [ 0, 0, 0 ];

// Iterate over each element in the array...
var i;
for ( i = 0; i < x.length; i++ ) {
    console.log( 'x[%s] = %d', idx.join( ',' ), x.get.apply( x, idx ) );
    idx = nextCartesianIndex.assign( x.shape, x.order, idx, -1, idx );
}

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

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.