# Python Program to Interchange Elements of First and Last Rows in Matrix

In the previous article, we have discussed Python Program for Squares of Matrix Diagonal Elements

Given a matrix, the task is to interchange the elements of the first and the last rows of a given matrix.

What is a matrix:

A matrix is a rectangular sequence of numbers divided into columns and rows. A matrix element or entry is a number that appears in a matrix.

Example:

Above is the matrix which contains 5 rows and 4 columns and having elements from 1 to 20.

In this order, the dimensions of a matrix indicate the number of rows and columns.

Here as there are 5 rows and 4 columns it is called a 5*4 matrix.

Examples:

Example1:

Input:

Given Matrix :
2 3 4
1 7 45
8 2 3

Output:

The given matix after swapping the first and last row elements:
8 2 3
1 7 45
2 3 4

Example2:

Input:

Given Matrix :
1 2 3
4 5 6
7 8 9

Output:

The given matix after swapping the first and last row elements:
7 8 9
4 5 6
1 2 3

## Program to Interchange Elements of First and Last Rows in Matrix in Python

Below are the ways to interchange the elements of the first and the last rows of a given matrix in python:

### Method #1: Using For Loop (Static Input)

Approach:

• Give the matrix as static input and store it in a variable.
• Calculate the number of rows of the given matrix by calculating the length of the nested list using the len() function and store it in a variable mtrxrows.
• Calculate the number of columns of the given matrix by calculating the length of the first list in the nested list using the len() function and store it in a variable mtrxcolums.
• Loop till the given number of rows using the For loop.
• Inside the For loop, swap mtrx[0][itr], mtrx[mtrxrows-1][itr] using the comma(,) operator ( where itr is the iterator value and mtrxrows is the no of rows of matrix).
• To print all the elements of the given matrix.
• Loop till the given number of rows using the For loop.
• Inside the For loop, Iterate till the given number of rows using another Nested For loop(Inner For loop).
• Print the element of the matrix by printingÂ gvnmatrix[n][m]Â value where n is the iterator value of the parent For loop and m is the iterator value of the inner For loop.
• The Exit of the Program.

Below is the implementation:

# Give the matrix as static input and store it in a variable.
mtrx = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
# Calculate the number of rows of the given matrix by
# calculating the length of the nested list using the len() function
# and store it in a variable mtrxrows.
mtrxrows = len(mtrx)
# Calculate the number of columns of the given matrix by
# calculating the length of the first list in the nested list
# using the len() function and store it in a variable mtrxcols.
mtrxcols = len(mtrx[0])
print("The given matix after swapping the first and last row elements: ")
# Loop till the given number of rows using the For loop.
for itr in range(mtrxrows):
# Inside the For loop, swap mtrx[0][itr], mtrx[mtrxrows-1][itr] using the comma(,) operator
# ( where itr is the iterator value and mtrxrows is the no of rows of matrix).

mtrx[0][itr], mtrx[mtrxrows-1][itr] = mtrx[mtrxrows-1][itr], mtrx[0][itr]

# Loop till the given number of rows using the For loop.
for n in range(mtrxrows):
# Inside the For loop, Iterate till the given number of rows using another
# Nested For loop(Inner For loop).
for m in range(mtrxcols):
# Print the element of the matrix by printing gvnmatrix[n][m] value
# where n is the iterator value of the parent For loop and m is the iterator
# value of the inner For loop.
print(mtrx[n][m], end=' ')
print()


Output:

The given matix after swapping the first and last row elements:
7 8 9
4 5 6
1 2 3

### Method #2: Using For loop (User Input)

Approach:

• Give the number of rows of the matrix as user input using the int(input()) function and store it in a variable.
• Give the number of columns of the matrix as user input using the int(input()) function and store it in another variable.
• Take a list and initialize it with an empty value using [] or list() to sayÂ gvnmatrix.
• Loop till the given number of rows using the For loop
• Inside the For loop, Give all the row elements of the given Matrix as a list using the list(),map(),int(),split() functions and store it in a variable.
• Add the above row elements list toÂ gvnmatrixÂ using the append() function.
• Loop till the given number of rows using the For loop.
• Inside the For loop, swap mtrx[0][itr], mtrx[mtrxrows-1][itr] using the comma(,) operator ( where itr is the iterator value and mtrxrows is the no of rows of matrix).
• To print all the elements of the given matrix.
• Loop till the given number of rows using the For loop.
• Inside the For loop, Iterate till the given number of rows using another Nested For loop(Inner For loop).
• Print the element of the matrix by printingÂ gvnmatrix[n][m]Â value where n is the iterator value of the parent For loop and m is the iterator value of the inner For loop.
• The Exit of the Program.

Below is the implementation:

# Give the number of rows of the matrix as user input using the int(input()) function
# and store it in a variable.
mtrxrows = int(input('Enter some random number of rows of the matrix = '))
# Give the number of columns of the matrix as user input using the int(input()) function
# and store it in another variable.
mtrxcols = int(input('Enter some random number of columns of the matrix = '))
# Take a list and initialize it with an empty value using [] or list() to say gvnmatrix.
mtrx = []
# Loop till the given number of rows using the For loop
for n in range(mtrxrows):
# Inside the For loop, Give all the row elements of the given Matrix as a list using
# the list(),map(),int(),split() functions and store it in a variable.
l = list(map(int, input(
'Enter {'+str(mtrxcols)+'} elements of row {'+str(n+1)+'} separated by spaces = ').split()))
# Add the above row elements list to gvnmatrix using the append() function.

mtrx.append(l)

print("The given matix after swapping the first and last row elements: ")
# Loop till the given number of rows using the For loop.
for itr in range(mtrxrows):
# Inside the For loop, swap mtrx[0][itr], mtrx[mtrxrows-1][itr] using the comma(,) operator
# ( where itr is the iterator value and mtrxrows is the no of rows of matrix).

mtrx[0][itr], mtrx[mtrxrows-1][itr] = mtrx[mtrxrows-1][itr], mtrx[0][itr]

# Loop till the given number of rows using the For loop.
for n in range(mtrxrows):
# Inside the For loop, Iterate till the given number of rows using another
# Nested For loop(Inner For loop).
for m in range(mtrxcols):
# Print the element of the matrix by printing gvnmatrix[n][m] value
# where n is the iterator value of the parent For loop and m is the iterator
# value of the inner For loop.
print(mtrx[n][m], end=' ')
print()

Output:

Enter some random number of rows of the matrix = 3
Enter some random number of columns of the matrix = 3
Enter {3} elements of row {1} separated by spaces = 2 3 4
Enter {3} elements of row {2} separated by spaces = 1 7 45
Enter {3} elements of row {3} separated by spaces = 8 2 3
The given matix after swapping the first and last row elements:
8 2 3
1 7 45
2 3 4

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