💡 Problem Formulation: This article demonstrates how to swap elements between the first and last rows of a two-dimensional matrix, using Python. Given a matrix, the aim is to replace the elements of the first row with those of the last row and vice versa. For example, if the input matrix is [[1, 2, 3], [4, 5, 6], [7, 8, 9]], the desired output should be [[7, 8, 9], [4, 5, 6], [1, 2, 3]].
Method 1: Using Indexing
The indexing method involves directly accessing the first and last rows by their index and swapping them. This method is straightforward and is one of the simplest ways to perform the required interchange.
Here’s an example:
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] matrix[0], matrix[-1] = matrix[-1], matrix[0] print(matrix)
Output:
[[7, 8, 9], [4, 5, 6], [1, 2, 3]]
In this snippet, matrix[0] refers to the first row, and matrix[-1] refers to the last row. The assignment matrix[0], matrix[-1] = matrix[-1], matrix[0] swaps the two rows in one line of code, providing an efficient solution.
Method 2: Using Tuple Unpacking
By employing tuple unpacking, we can achieve the interchange of the first and last rows of the matrix in a clear and Pythonic way. The rows are treated as tuples and they are unpacked and repacked in the desired order.
Here’s an example:
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] first_row, *middle_rows, last_row = matrix matrix = [last_row] + middle_rows + [first_row] print(matrix)
Output:
[[7, 8, 9], [4, 5, 6], [1, 2, 3]]
This code first unpacks the matrix into the first row, middle rows, and the last row. The new matrix is then constructed by repacking the rows in the order of the last row, middle rows, and the first row.
Method 3: Using a Function
Creating a separate function to swap rows encapsulates our logic and offers reusability. This approach also improves code readability and makes complex matrix operations more manageable.
Here’s an example:
def swap_first_last(matrix):
matrix[0], matrix[-1] = matrix[-1], matrix[0]
return matrix
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
print(swap_first_last(matrix))
Output:
[[7, 8, 9], [4, 5, 6], [1, 2, 3]]
The function swap_first_last() takes a matrix as input, swaps the first and last rows, and returns the modified matrix. When called with our example matrix, it produces the desired result.
Method 4: Using Slicing
Matrix slicing in Python allows us to select rows and columns with ease. In this method, we use slicing to isolate the first and last rows, and then reassemble the matrix with the rows swapped.
Here’s an example:
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] matrix = [matrix[-1]] + matrix[1:-1] + [matrix[0]] print(matrix)
Output:
[[7, 8, 9], [4, 5, 6], [1, 2, 3]]
Slicing here allows us to directly define the new order of the matrix rows, with the first element being the last row of the original matrix, followed by the middle rows, and finalized with the original first row.
Bonus One-Liner Method 5: Using List Comprehension
Python’s list comprehension provides a concise way to create lists. Below is a creative one-liner that utilizes list comprehensions to perform the row interchange.
Here’s an example:
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] matrix = [row if i != 0 and i != len(matrix) - 1 else matrix[-i] for i, row in enumerate(matrix)] print(matrix)
Output:
[[7, 8, 9], [4, 5, 6], [1, 2, 3]]
This one-liner iterates over the matrix rows and for each row, it decides whether to keep the current row or to swap it with the last row, based on the index i.
Summary/Discussion
- Method 1: Indexing. Simple and direct. Can be less clear in more complex operations.
- Method 2: Tuple Unpacking. Pythonic and clear. Creates additional variables which may confuse in more complex data manipulations.
- Method 3: Using a Function. Very good for repeated tasks and improves readability. Slightly overkill for one-time operations.
- Method 4: Slicing. Flexible and handy for more complex slicing operations. Can be less intuitive for beginners.
- Bonus Method 5: List Comprehension. Extremely concise. Can be cryptic and harder to debug for complex logic.