Python program: Swap the positions of the first and last elements in a matrix between columns

A matrix is ​​a two-dimensional array consisting of many numbers arranged in rows and columns. Python does not have any data type to represent matrices, but we can use nested lists or NumPy arrays as matrices.

See the following input and output scenarios to learn how to swap the first and last column elements of the matrix.

Input and output scenarios

Suppose we have a 3X3 matrix represented using a list of lists. The output matrix will be the resulting matrix of swapping the first and last column elements.

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 another matrix where the rows and columns are not equal.

Input matrix: 
['a', 'b']
['c', 'd', 'e']
['f', 'g', 'h', 'i']

Output matrix: 
['b', 'a']
['e', 'd', 'c']
['i', 'g', 'h', 'f']

Let's look at different ways of swapping the first and last elements in a matrix across columns.

Exchange columns

We can simply swap the first and last elements in the matrix across columns by swapping the first and last column elements of the matrix.

Example

Create a matrix using a list of lists so that we can apply list indexing techniques to swap elements.

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

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

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

# swap column elements
def swapColumns(matrix):
   for i in range(len(matrix)):
      t = matrix[i][0]
      matrix[i][0] = matrix[i][-1]
      matrix[i][-1] = t
   return matrix

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

Output

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

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

The given matrix is ​​a square matrix and we have successfully swapped the first and last elements of the given matrix across columns, this is done by using python positive and negative indexing.

Example

In this example, we will swap the column elements of a non-square matrix.

matrix = [['a', 'b'], ['c', 'd', 'e'], ['f', 'g', 'h', 'i']]

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

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

# swap column elements
def swapColumns(matrix):
   for i in range(len(matrix)):
      t = matrix[i][0]
      matrix[i][0] = matrix[i][-1]
      matrix[i][-1] = t
   return matrix

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

Output

Original matrix: 
['a', 'b']
['c', 'd', 'e']
['f', 'g', 'h', 'i']

Changed matrix: 
['b', 'a']
['e', 'd', 'c']
['i', 'g', 'h', 'f']

Use a for loop to iterate over the matrix rows and swap column elements using the index.

Use list operation methods

In Python, pop(), insert() and append() are list operation methods. And the matrix is ​​created using a list of lists so that we can swap the first and last elements of the matrix across columns using these list manipulation methods.

• pop() - The pop method deletes the element at the specified position. By default it removes the last element.

grammar

list_obj.pop(index)

• insert() - This method can be used to insert an element at any desired position. This method accepts two parameters, an element and the index at which the element must be inserted.

grammar

list_obj.insert(index, element)

• append() - Method is used to add an element at the end of the list.

grammar

list_obj.append(item)

Example

Let us take an example and apply the pop(), insert() and append() methods.

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

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

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

# interchanging the element between first and last columns
for row in matrix:
   temp1 = row[-1]
   temp2 = row[0]
   row.pop()
   row.pop(0)
   row.insert(0, temp1)
   row.append(temp2)

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

Output

Original matrix: 
[1, 3]
[4, 5, 6]
[7, 8, 3, 9]

Changed matrix: 
[3, 1]
[6, 5, 4]
[9, 8, 3, 7]

Using temporary variables and list manipulation methods, we successfully swapped column elements.

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