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How to rotate a matrix?

Posted on May 12, 2021April 5, 2022 By Luke K

Let’s learn how to rotate a matrix in Numpy. We are going to see a few tricks in that matter.
Numpy rotate over axes

Rotation by 90 degrees

With Numpy it is very easy to rotate matrix 90 degrees. There is dedicated rot90 Numpy method.

import numpy as np

my_array = np.array([[11, 12, 13],
                    [21, 22, 23],
                    [31, 32, 33]])
print(f"This is my array: \n{my_array}")

rotate_array = np.rot90(my_array)
print(f"Array rotated:  \n{rotate_array}")

Numpy how to rotate array

Rotation by 270 degrees

To rotate 270 degrees just add 3 as a parameter to rot90 function. This parameter makes 3 rounds of 90 degrees rotation (counter clockwise).

import numpy as np

my_array = np.array([[11, 12, 13],
                    [21, 22, 23],
                    [31, 32, 33]])
print(f"This is my array: \n{my_array}")

rotate_array = np.rot90(my_array, 3)
print(f"Array rotated 270 degrees:  \n{rotate_array}")

Numpy array rotate 270 degrees

This is 270 degrees rotation but we can also say that this is left rotation because this is how to rotate an matrix left direction.

See also  How to append to empty array in Numpy?

Rotation by 180 degrees

To rotate 180 put np.rot90(my_array, 2). Having np.rot90(my_array, 4) will not change the array at all.

You can also rotate an array over the axes.

import numpy as np

my_array = np.array([[11, 12, 13],
                    [21, 22, 23],
                    [31, 32, 33]])
print(f"This is my array: \n{my_array}")

rotate_array = np.rot90(my_array, axes=(1, 0))
print(f"Array rotated over axes=(1, 0):  \n{rotate_array}")

Numpy rotate over axes

I used np.rot90(my_array, axes=(1, 0)) and this is how it got rotated.

See also  Incredible trick on how to reshape to automatic value of dimension in Numpy
numpy Tags:array, axis, rotate

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