Python matrix, matrice Python senza usare Numpy

In Python we can create matrix using a double for loop, or we can just use the Numpy library.

In this lesson we will create arrays using iterative instructions, later we will see the use of Numpy.

Python matrix – first exercise

In this first exercise we use a double for loop to create arrays with random numbers.

In particular, we will create a 3 x 3 matrix, but then we will generalize the algorithm by creating matrices of custom size.

First of all, since I have to generate random numbers, I import the random module and in particular randint.

After, I create an empty list and with the first for loop I go through all the lines. For each line it uses another for loop and I generate a list of 3 random numbers. At the end of the innermost loop I use Python’s append method to append the generated list to the starting matrix.

Here is a possible solution to create matrix in Python:


from random import randint

matrix = []

for i in range(3):
    n = []
    for j in range(3):
        number = randint(1,100)
        n.insert(i,number)

    matrix.append(n)


print(matrix)

We can populate an array with a while loop, but that’s not the optimal solution. In fact, remember that when we know exactly how many times a loop must be executed, we use the for. The while is used instead when I need to satisfy a condition.


from random import randint
matrix = []
i=0
while i < 3:
    j = 0
    n = []
    while j < 3:
        number = randint(1,100)
        n.insert(i,number)
        j = j+1
    matrix.append(n)
    i = i+1
print(matrix)

Let’s now create a function in Python to generate a matrix:


from random import randint

def matrix(x,y):
    matrix = []
    
    for i in range(x):
        n = []

        for j in range(y):
            number = randint(1,100)
            n.insert(i,number)

        matrix.append(n)

    return matrix
    

print(matrix(3,3))

In this way we can generate matrices of any size.

Python matrix – second exercise

We ask the user as input for the size of the matrix to be generated.


from random import randint

def matrix(x,y):
    matrix = []
    
    for i in range(x):
        n = []

        for j in range(y):
            number = randint(1,100)
            n.insert(i,number)

        matrix.append(n)

    return matrix

x = int(input('enter the x dimension of the matrix '))
y = int(input('enter the y dimension of the matrix '))

print(matrix(x,y))

Let’s try the code just generated in the compiler below:

In this Python lesson we developed matrix by simply using a double for loop. In the next few lessons we will study Numpy.

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