taking n*n matrix input by user in python

Question

I am starting to code in python. When I was to take two inputs from user with a space between the two inputs my code was like

 min, p = input().split(" ") 
min=int(min)
p=float(p)

which worked fine. In another such problem I am to take a n*n matrix as user input which I declared as arr=[[0 for i in range(n)] for j in range(n)] printing the arr gives a fine matrix(in a single row though) but I am to replace each element '0'with a user input so I use nested loops as

for i in range(0,n)
 for j in range(0,n)
 arr[i][j]=input()

this also worked fine but with a press of 'enter' button after each element. In this particular problem the user will input elements in one row at space instead of pressing 'enter' button. I wanted to know how to use split in this case like in first case above, keeping in mind the matrix is n*n where we don't know what is n. I prefer to avoid using numpy being a beginner with python.

• Youka: What stops you from reading an input line, splitting her to a list, checking number of elements and possible conversion to numbers and copying them to your matrix as one row?

Answer 1

You can do this:

rows = int(input("Enter number of rows in the matrix: "))
columns = int(input("Enter number of columns in the matrix: "))
matrix = []
print("Enter the %s x %s matrix: "% (rows, columns))
for i in range(rows):
 matrix.append(list(map(int, input().rstrip().split())))

Now you input in the console values like this:

Enter number of rows in the matrix: 2
Enter number of columns in the matrix: 2
Enter the 2 x 2 matrix:
1 2
3 4

Answer 2

#Take matrix size as input
n=int(input("Enter the matrix size"))
import numpy as np
#initialise nxn matrix with zeroes
mat=np.zeros((n,n))
#input each row at a time,with each element separated by a space
for i in range(n):
 mat[i]=input().split(" ")
print(mat) 

Answer 3

You can try this simple approach (press enter after each digit...works fine)::

m1=[[0,0,0],[0,0,0],[0,0,0]]
for x in range (0,3):
 for y in range (0,3):
 m1[x][y]=input()
print (m1)

• Mohsen_Fatemi: and if you want to enter 1000*1000 matrix what should you do ?
• Pratik Vyas: just change the values in range (for loops) for both 'row for loop' and 'column for loop': "for x in range (0,1000)" and "for y in range (0,1000)"
• Mohsen_Fatemi: so describe it in your answer

Answer 4

Try something like this instead of setting the matrix one by one using existing list(s):

# take input from user in one row
nn_matrix = raw_input().split()
total_cells = len(nn_matrix)
# calculate 'n'
row_cells = int(total_cells**0.5)
# calculate rows
matrix = [nn_matrix[i:i+row_cells] for i in xrange(0, total_cells, row_cells)]

Example:

>>> nn_matrix = raw_input().split()
1 2 3 4 5 6 7 8 9
>>> total_cells = len(nn_matrix)
>>> row_cells = int(total_cells**0.5)
>>> matrix = [nn_matrix[i:i+row_cells] for i in xrange(0, total_cells, row_cells)]
>>> matrix
[['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']]
>>> 

Answer 5

>>> import math
>>> line = ' '.join(map(str, range(4*4))) # Take input from user
'0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15'
>>> items = map(int, line.split()) # convert str to int
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
>>> n = int(math.sqrt(len(items))) # len(items) should be n**2
4
>>> matrix = [ items[i*n:(i+1)*n] for i in range(n) ]
[[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11], [12, 13, 14, 15]]

Answer 6

Well if matrix is n*n that means with first input line you know number of input lines (and no, it's impossible for input() to not end with key enter is pressed). So you need something like this:

arr = []
arr.append(input().split())
for x in range(len(arr[0]) - 1):
 arr.append(input().split())

I used range(len(arr[0]) - 1) so it inputs rest of lines (because matrix width and height is same and one first line is already read from input).

Also I used .split() without " " as parameter because it's default parameter.

Answer 7

Try with below,

r=int(input("enter number of rows"));
c=int(input("enter number of columns"));
mat=[];
for row in range(r):
 a=[]
 for col in range(c):
 a.append(row*col);
 mat.append(a)
print mat;

Answer 8

print("Enter The row and column :")
row,col=map(int,input().split())
matrix = [] 
print("Enter the entries rowwise:") 
# For user input 
for i in range(row): # for loop for row entries 
a =[] 
for j in range(col): # for loop for column entries 
 a.append(int(input())) 
matrix.append(a) 
for i in range(row): 
 for j in range(col): 
 print(matrix[i][j], end = " ") 
print()

• Agnel Vishal: Code not intended
• Suraj Verma: You can copy and paste this as it is ,then it will run
• Agnel Vishal: a =[] is not intended

Answer 9

n= 10 # n is the order of the matrix

matrix = [[int(j) for j in input().split()] for i in range(n)]

print(matrix)

Answer 10

r = int(input("Enret Number of Raws : "))
c = int(input("Enter Number of Cols : "))
a=[]
for i in range(r):
 b=[]
 for j in range(c):
 j=int(input("Enter Number in pocket ["+str(i)+"]["+str(j)+"]"))
 b.append(j)
 a.append(b)
for i in range(r):
 for j in range(c):
 print(a[i][j],end=" ")
 print()