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rot90

Rotate an ndarray 90 degrees in a specified plane.

Usage

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

rot90( x, dims, k, writable )

Rotates an ndarray 90 degrees in the plane specified by two dimension indices.

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 ] ]