Python program to swap elements of matrix diagonal, using predefined method

The diagonal is the cross element in the matrix.

A square matrix has two diagonals. One is the main diagonal - from the upper left corner to the lower right corner of the square. The other is the subdiagonal - from the upper right corner to the lower left corner of the square.

Swapping the diagonal simply changes the main and sub-diagonal elements of the matrix.

Please check out the following scenario for a brief understanding

Input and output scenarios

Suppose we have a square matrix. The output matrix will be the result matrix with its diagonals swapped.

Input matrix: 
[1, 3, 4]
[4, 5, 6]
[7, 8, 3]
Output matrix: 
[4, 3, 1]
[4, 5, 6]
[3, 8, 7]

Let us consider a 4X4 matrix.

Input matrix: 
['o', 't', 'l', 'K']
['v', 'P', 's', 'm']
['E', 's', 'X', 'c']
['e', 'p', 'O', 'j']

Output matrix: 
['K', 't', 'l', 'o']
['v', 's', 'P', 'm']
['E', 's', 'X', 'c']
['j', 'p', 'O', 'e']

Using Python list methods

In Python, the index(), pop(), insert() and append() methods are all list methods. And here, the matrix is ​​created by using a list of lists so that we can use these list methods to swap the diagonals.

• index() − The index() method returns the position of the first occurrence of a given value.

• pop() − The pop method will remove the element at the specified position. By default it removes the last element.

• insert() − This method can be used to insert elements at any position. This method accepts two parameters, one is the element to be inserted and the other is the index of the position to be inserted.

• append() − method is used to add an element to the end of the list.

Example

In this example, the display() function will print the given matrix. And the exchangeDiagonals() function will exchange elements.

#function for displaying matrix
def display(matrix):
   for row in matrix:
      print(row)
   print()

# interchanging the diagonals elements
def interchangeDiagonals(matrix):
   for row in matrix:
      if matrix.index(row) != len(matrix) // 2:
         temp1 = row[-1]
         temp2 = row[0]
         row.pop()
         row.pop(0)
         row.insert(0, temp1)
         row.append(temp2)
   return matrix

# input matrix
matrix = [[1, 3, 4], [4, 5, 6], [7, 8, 3]]

# displaying original matrix
print("Original matrix: ")
display(matrix) 

# displaying changed matrix
print("Changed matrix: ")
display(interchangeDiagonals(matrix))

Output

Original matrix: 
[1, 3, 4]
[4, 5, 6]
[7, 8, 3]

Changed matrix: 
[4, 3, 1]
[4, 5, 6]
[3, 8, 7]

By using Python list methods, we successfully swapped the diagonal elements of the given matrix.

Note− The above method only applies to 3X3 matrices.

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