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rot90

Rotate an ndarray 90 degrees in a specified plane.

Installation

npm install @stdlib/ndarray-base-rot90

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 rot90 = require( '@stdlib/ndarray-base-rot90' );

rot90( x, dims, k, writable )

Rotates an ndarray 90 degrees in a specified plane.

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

var x = array( [ [ 1, 2 ], [ 3, 4 ] ] );
// returns <ndarray>[ [ 1, 2 ], [ 3, 4 ] ]

var y = rot90( x, [ 0, 1 ], 1, false );
// returns <ndarray>[ [ 2, 4 ], [ 1, 3 ] ]

The function accepts the following arguments:

• x: input ndarray.
• dims: dimension indices defining the plane of rotation. Must contain exactly two unique dimension indices. If a dimension index is provided as an integer less than zero, the dimension index is resolved relative to the last dimension, with the last dimension corresponding to the value -1.
• k: number of times to rotate by 90 degrees. Positive values rotate counterclockwise. Negative values rotate clockwise.
• writable: boolean indicating whether a returned ndarray should be writable.

Notes

• If k > 0, the function rotates the plane from the first specified dimension toward the second specified dimension. This means that, for a two-dimensional ndarray and dims = [0, 1], the function rotates the plane counterclockwise.
• If k < 0, the function rotates the plane from the second specified dimension toward the first specified dimension. This means that, for a two-dimensional ndarray and dims = [1, 0], the function rotates the plane clockwise.
• Each provided dimension index must reside on the interval [-ndims, ndims-1].
• The writable parameter only applies to ndarray constructors supporting read-only instances.
• The returned ndarray is a view of the input ndarray. Accordingly, writing to the original ndarray will mutate the returned ndarray and vice versa.

Examples

var array = require( '@stdlib/ndarray-array' );
var ndarray2array = require( '@stdlib/ndarray-to-array' );
var rot90 = require( '@stdlib/ndarray-base-rot90' );

// Create a 2x3 matrix:
var x = array( [ [ 1, 2, 3 ], [ 4, 5, 6 ] ] );

// Rotate 90 degrees counterclockwise in the (0,1) plane:
var y = rot90( x, [ 0, 1 ], 1, false );
var arr = ndarray2array( y );
// returns [ [ 3, 6 ], [ 2, 5 ], [ 1, 4 ] ]

// Rotate 180 degrees:
y = rot90( x, [ 0, 1 ], 2, false );
arr = ndarray2array( y );
// returns [ [ 6, 5, 4 ], [ 3, 2, 1 ] ]

// Rotate 270 degrees counterclockwise (equivalent to k=-1):
y = rot90( x, [ 0, 1 ], 3, false );
arr = ndarray2array( y );
// returns [ [ 4, 1 ], [ 5, 2 ], [ 6, 3 ] ]

// Rotate 360 degrees (equivalent to no rotation):
y = rot90( x, [ 0, 1 ], 4, false );
arr = ndarray2array( y );
// returns [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]

// Rotate 90 degrees clockwise (equivalent to k=3):
y = rot90( x, [ 0, 1 ], -1, false );
arr = ndarray2array( y );
// returns [ [ 4, 1 ], [ 5, 2 ], [ 6, 3 ] ]

// Supports negative dimension indices:
y = rot90( x, [ -2, -1 ], 1, false );
arr = ndarray2array( y );
// returns [ [ 3, 6 ], [ 2, 5 ], [ 1, 4 ] ]

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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 © 2016-2026. The Stdlib Authors.