A matrix is a two-dimensional data structure where numbers are arranged into rows and columns. For example:
This matrix is a 3x4 (pronounced "three by four") matrix because it has 3 rows and 4 columns.
Python Matrix
Python doesn't have a built-in type for matrices. However, we can treat a list of a list as a matrix. For example:
A = [[1, 4, 5],
[-5, 8, 9]]
We can treat this list of a list as a matrix having 2 rows and 3 columns.
Be sure to learn about Python lists before proceed this article.
Let's see how to work with a nested list.
A = [[1, 4, 5, 12],
[-5, 8, 9, 0],
[-6, 7, 11, 19]]
print("A =", A)
print("A[1] =", A[1]) # 2nd row
print("A[1][2] =", A[1][2]) # 3rd element of 2nd row
print("A[0][-1] =", A[0][-1]) # Last element of 1st Row
column = []; # empty list
for row in A:
column.append(row[2])
print("3rd column =", column)
When we run the program, the output will be:
A = [[1, 4, 5, 12], [-5, 8, 9, 0], [-6, 7, 11, 19]] A[1] = [-5, 8, 9, 0] A[1][2] = 9 A[0][-1] = 12 3rd column = [5, 9, 11]
Here are few more examples related to Python matrices using nested lists.