90° Matrix Rotation Python

Question

I cannot understand why retrieved value of original Matrix isn't the good one. For instance, value of Matrix[0,3] should give 3 but gives 0 so that I am unable to get the correct 90° Matrix rotation:

import numpy as np
x = np.matrix(np.arange(16).reshape((4,4)))
print(x)

def rotate_90(matrix):
    rot_Mat = matrix
    len = matrix.shape[0]
    # len_range = range(len)
    # rev_range = reversed(len_range)
    for i in range(0, len):
        for j in range(0, len):

            value = matrix[i,j]
            print(i , j , value)
            
            rot_Mat[j,len - i -1] = value
    print(rot_Mat)

rotate_90(x)

It's on line 13, I enter Matrix in the function rotate_90 and the value of matrix[0,3] is printed on line 14 — Alan, Apr 03 '21 at 20:20

score 0 · Accepted Answer · answered Apr 03 '21 at 20:22

0

rot_Mat = matrix

This does not create a new array. rot_Mat is the same array as matrix, therefore you overwrite the values while reading them.

To create a new array with the same shape, use empty_like:

rot_Mat = np.empty_like(matrix)

answered Apr 03 '21 at 20:22

mkrieger1

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90° Matrix Rotation Python

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