Creating a random matrix in python

Question

I am trying to create a random square matrix of nxn random numbers with numpy. Of course I am able to generate enough random numbers but I am having trouble using numpy to create a matrix of variable length. This is as far as I have gotten thus far:

def testMatrix(size):
    a = []
    for i in range(0, size*size):
        a.append(randint(0, 5))

How can I put this list into an array of size x size?

What about numpy.random.randint(0, 5, size=(s,s))? Other approaches would be for example numpy.array(a).reshape((s,s)) (if a is flat = 1d). — sascha
– sascha, Commented Feb 3, 2018 at 0:30

xXx · Accepted Answer · 2022-09-30 07:57:50Z

4

Try

np.random.randint(0, 5, size=(s, s))

edited Sep 30, 2022 at 7:57

xXx

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answered Feb 3, 2018 at 0:32

ChootsMagoots

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Comments

kooshywoosh · Accepted Answer · 2018-02-03 00:58:43Z

0

Your test matrix is currently one dimensional. If you want to create a random matrix with numpy, you can just do:

num_rows = 3
num_columns = 3
random_matrix = numpy.random.random((num_rows, num_columns))

The result would be:

array([[ 0.15194989,  0.21977027,  0.85063633],
   [ 0.1879659 ,  0.09024749,  0.3566058 ],
   [ 0.18044427,  0.59143149,  0.25449112]])

You can also create a random matrix without numpy:

import random

num_rows = 3
num_columns = 3
random_matrix = [[random.random() for j in range(num_rows)] for i in range(num_columns)]

The result would be:

[[0.9982841729782105, 0.9659048749818827, 0.22838327707784145], 
[0.3524666409224604, 0.1918744765283834, 0.7779130503458696], 
[0.5239230720346117, 0.0224389713805887, 0.6547162177880549]]

Per the comments, I've added a function to convert a one dimensional array to a matrix:

def convert_to_matrix(arr, chunk_size):
    return [arr[i:i+chunk_size] for i in range(0, len(arr), chunk_size)]

arr = [1,2,3,4,5,6,7,8,9]
matrix = convert_to_matrix(arr, 3)
# [[1, 2, 3], [4, 5, 6], [7, 8, 9]] is the output

edited Feb 3, 2018 at 0:58

answered Feb 3, 2018 at 0:42

kooshywoosh

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4 Comments

J.Doe Over a year ago

That solution works perfectly for the question asked thanks! How would I modify that approach if my array was like a set of unique numbers 0 to n*n in a shuffled order. Is there a way to wrap an array into a numpy matrix?

kooshywoosh Over a year ago

@J.Doe If I'm understanding correctly, you want to take a shuffled one dimensional array and turn it into a numpy matrix? i.e. turn [4,3,2,1] into array([[4,3],[2,1]])

J.Doe Over a year ago

Sure that would accomplish it

kooshywoosh Over a year ago

@J.Doe Will add to my answer

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