How to Transpose a Matrix in Python (List of Lists)

Swap rows and columns of a 2D list using nested loops to produce a transposed matrix.

Easy Python 3.6+ Aug 9, 2026 Lists & loops 13 views 0 copies

matrix transpose 2d-list nested-loops list-of-lists

Python code

29 lines

Python 3.6+

def transpose(matrix):
    # Number of rows and columns in the original matrix
    rows = len(matrix)
    cols = len(matrix[0]) if rows > 0 else 0
    
    # Create a new matrix with dimensions swapped
    result = []
    for j in range(cols):
        new_row = []
        for i in range(rows):
            new_row.append(matrix[i][j])
        result.append(new_row)
    return result


if __name__ == "__main__":
    # Example 3x2 matrix
    original = [
        [1, 2, 3],
        [4, 5, 6]
    ]
    
    transposed = transpose(original)
    print("Original matrix:")
    for row in original:
        print(row)
    print("\nTransposed matrix:")
    for row in transposed:
        print(row)

Output

stdout

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

Transposed matrix:
[1, 4]
[2, 5]
[3, 6]

How it works

The function determines the number of rows and columns from the input matrix. It then creates a result list with one row for each column of the original. Each new row is built by collecting the element at the same column index across all original rows, effectively swapping indices. This approach works for any rectangular matrix and leaves the original untouched. The outer loop iterates over columns, and the inner loop over rows, giving the transposed shape.

Common mistakes

Forgetting to check for an empty matrix, leading to IndexError
Assuming the matrix is square; the code handles rectangular matrices correctly
Modifying the original matrix while transposing
Using list comprehension incorrectly, which may be less readable for beginners

Variations

Use `list(zip(*matrix))` to transpose with the zip function
Use a list comprehension: `[[row[j] for row in matrix] for j in range(len(matrix[0]))]`

Real-world use cases

Preparing data for machine learning by converting feature rows to columns.
Reformatting spreadsheet data where rows and columns need to be swapped for analysis.
Rotating a grid-based game board by transposing its 2D array representation.

How to Transpose a Matrix in Python (List of Lists)

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Lists & loops

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