Mirror of Matrix Across Diagonal in Python

The mirror of a matrix across a diagonal means swapping the elements at position[i, j] with the elements at position[j, i]. 

Problem statement

You are given a 2-D matrix in Python in the form of a nested List, and you need to find the transpose, that is, the mirror is that matrix across the diagonal.

Example

Input: 
matrix = 
[[1, 2, 3],

[4, 5, 6],

[7, 8, 9]]

Output:
[[1, 4, 7],

[2, 5, 8],

[3, 6, 9]]

Mirror of a Matrix Using Nested for Loop

In this approach, we will use the nested for loop to find the mirror of the matrix across a diagonal.

Example

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

print("Original Matrix")
print(matrix)

# new nested list to store mirrormatrix
mirror_matrix = [[0 for i in range(len(matrix))] for j in range(len(matrix[0]))]

# nested for loop to iterate through lists
for i in range(len(matrix)):
    for j in range(len(matrix[0])):
        mirror_matrix[j][i] = matrix[i][j]

print("Mirror Matrix")
print(mirror_matrix)

Output

Original Matrix
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Mirror Matrix
[[1, 4, 7], [2, 5, 8], [3, 6, 9]]

Mirror of a Matrix Using List Comprehension

In this approach, we will use the concept of list comprehension to find the mirror of the matrix across a diagonal.

Example

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

print("Original Matrix")
print(matrix)

# mirror matrix using list comprehension
mirror_matrix = [
    [matrix[i][j] for i in range(len(matrix))] for j in range(len(matrix[0]))
]

print("Mirror Matrix")
print(mirror_matrix)

Output

Original Matrix
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Mirror Matrix
[[1, 4, 7], [2, 5, 8], [3, 6, 9]]