How to create a random matrix (without using numpy)?

Question

I am trying to create an array. When the number of rows and columns are not same, an empty [] appears at the end.

I also want it to be displayed in correct matrix form of [m x n]

I am new to using Python language and this is my first question.

I hope to find a solution to the problem.

import random

m = int(input("Rows : "))
n = int(input("Columns : "))
Mat = []
for i in range(0,n):
    Mat.append([])
for i in range(0,m):
    for j in range(0,n):
        Mat[i].append(j)
        Mat[i][j] = 0
        Mat[i][j] = random.randint(1,100)
print(Mat)

Example:

Columns : 2
Rows : 3

Output:

[[7, 49, 61], [47, 2, 40], []]

I need it like this:

[[7, 49, 61],
 [47, 2, 40]]

mat = [[random.randint(1, 100) for _ in range(n)] for _ in range(m)] — Oleg Vorobiov
– Oleg Vorobiov, Commented Oct 11, 2019 at 17:08
you are not going to get the same kind of output, for your mat, as a numpy array when you print it out. unless you are using pprint.pprint(mat) or similar to print out mat. — Oleg Vorobiov
– Oleg Vorobiov, Commented Oct 11, 2019 at 17:15
In your inner loop, you could just be doing this instead of those three lines Mat[i].append(random.randint(1,100)) but the list comprehension above is much better — Dan
– Dan, Commented Oct 11, 2019 at 17:15

Prune · Accepted Answer · 2019-10-11 17:09:06Z

2

The problem is here, where you specifically add one row for every column the user requests:

for i in range(0,n):
    Mat.append([])

Instead, use the variable for rows:

for i in range(0, m):
    Mat.append([])

There are several places where you are doing extra work, such as setting a value and then immediately destroying it.

answered Oct 11, 2019 at 17:09

Prune

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2 Comments

mr Mad Over a year ago

Thank you mr Prune

Prune Over a year ago

Note that this is a fix for only the immediate problem. The various comments are very good refinements for your code.

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