I tried to create this code to input an m by n matrix. I intended to input [[1,2,3],[4,5,6]]
but the code yields [[4,5,6],[4,5,6]
. Same things happen when I input other m by n matrix, the code yields an m by n matrix whose rows are identical.
Perhaps you can help me to find what is wrong with my code.
m = int(input('number of rows, m = '))
n = int(input('number of columns, n = '))
matrix = []; columns = []
# initialize the number of rows
for i in range(0,m):
matrix += [0]
# initialize the number of columns
for j in range (0,n):
columns += [0]
# initialize the matrix
for i in range (0,m):
matrix[i] = columns
for i in range (0,m):
for j in range (0,n):
print ('entry in row: ',i+1,' column: ',j+1)
matrix[i][j] = int(input())
print (matrix)
This code takes number of row and column from user then takes elements and displays as a matrix.
m = int(input('number of rows, m : '))
n = int(input('number of columns, n : '))
a=[]
for i in range(1,m+1):
b = []
print("{0} Row".format(i))
for j in range(1,n+1):
b.append(int(input("{0} Column: " .format(j))))
a.append(b)
print(a)
If you want to take n lines of input where each line contains m space separated integers like:
1 2 3
4 5 6
7 8 9
Then you can use:
a=[] // declaration
for i in range(0,n): //where n is the no. of lines you want
a.append([int(j) for j in input().split()]) // for taking m space separated integers as input
Then print whatever you want like for the above input:
print(a[1][1])
O/P would be 5 for 0 based indexing
I used numpy library and it works fine for me. Its just a single line and easy to understand. The input needs to be in a single size separated by space and the reshape converts the list into shape you want. Here (2,2) resizes the list of 4 elements into 2*2 matrix. Be careful in giving equal number of elements in the input corresponding to the dimension of the matrix.
import numpy as np
a=np.array(list(map(int,input().strip().split(' ')))).reshape(2,2)
print(a)
Input
array([[1, 2],
[3, 4]])
Output
you can accept a 2D list in python this way ...
simply
arr2d = [[j for j in input().strip()] for i in range(n)]
# n is no of rows
for characters
n = int(input().strip())
m = int(input().strip())
a = [[0]*n for _ in range(m)]
for i in range(n):
a[i] = list(input().strip())
print(a)
or
n = int(input().strip())
n = int(input().strip())
a = []
for i in range(n):
a[i].append(list(input().strip()))
print(a)
for numbers
n = int(input().strip())
m = int(input().strip())
a = [[0]*n for _ in range(m)]
for i in range(n):
a[i] = [int(j) for j in input().strip().split(" ")]
print(a)
where n is no of elements in columns while m is no of elements in a row.
In pythonic way, this will create a list of list
m,n=map(int,input().split()) # m - number of rows; n - number of columns;
matrix = [[int(j) for j in input().split()[:n]] for i in range(m)]
for i in matrix:print(i)
no_of_rows = 3 # For n by n, and even works for n by m but just give no of rows
matrix = [[int(j) for j in input().split()] for i in range(n)]
print(matrix)
row=list(map(int,input().split())) #input no. of row and column
b=[]
for i in range(0,row[0]):
print('value of i: ',i)
a=list(map(int,input().split()))
print(a)
b.append(a)
print(b)
print(row)
Output:
2 3
value of i:0
1 2 4 5
[1, 2, 4, 5]
value of i: 1
2 4 5 6
[2, 4, 5, 6]
[[1, 2, 4, 5], [2, 4, 5, 6]]
[2, 3]
Note: this code in case of control.it only control no. Of rows but we can enter any number of column we want i.e row[0]=2
so be careful. This is not the code where you can control no of columns.
Apart from the accepted answer, you can also initialise your rows in the following manner -
matrix[i] = [0]*n
Therefore, the following piece of code will work -
m = int(input('number of rows, m = '))
n = int(input('number of columns, n = '))
matrix = []
# initialize the number of rows
for i in range(0,m):
matrix += [0]
# initialize the matrix
for i in range (0,m):
matrix[i] = [0]*n
for i in range (0,m):
for j in range (0,n):
print ('entry in row: ',i+1,' column: ',j+1)
matrix[i][j] = int(input())
print (matrix)
Creating matrix with prepopulated numbers can be done with list comprehension. It may be hard to read but it gets job done:
rows = int(input('Number of rows: '))
cols = int(input('Number of columns: '))
matrix = [[i + cols * j for i in range(1, cols + 1)] for j in range(rows)]
with 2 rows and 3 columns matrix will be [[1, 2, 3], [4, 5, 6]], with 3 rows and 2 columns matrix will be [[1, 2], [3, 4], [5, 6]] etc.
You can make any dimension of list
list=[]
n= int(input())
for i in range(0,n) :
#num = input()
list.append(input().split())
print(list)
output:
a,b=[],[]
n=int(input("Provide me size of squre matrix row==column : "))
for i in range(n):
for j in range(n):
b.append(int(input()))
a.append(b)
print("Here your {} column {}".format(i+1,a))
b=[]
for m in range(n):
print(a[m])
works perfectly
rows, columns = list(map(int,input().split())) #input no. of row and column
b=[]
for i in range(rows):
a=list(map(int,input().split()))
b.append(a)
print(b)
input
2 3
1 2 3
4 5 6
output [[1, 2, 3], [4, 5, 6]]
If your matrix is given in row manner like below, where size is s*s here s=5
5
31 100 65 12 18 10 13 47 157 6 100 113 174 11 33 88 124 41 20 140 99 32 111 41 20
then you can use this
s=int(input())
b=list(map(int,input().split()))
arr=[[b[j+s*i] for j in range(s)]for i in range(s)]
your matrix will be 'arr'
a = []
b = []
m=input("enter no of rows: ")
n=input("enter no of coloumns: ")
for i in range(n):
a = []
for j in range(m):
a.append(input())
b.append(a)
Input : 1 2 3 4 5 6 7 8 9
Output : [ ['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9'] ]
If the input is formatted like this,
1 2 3
4 5 6
7 8 9
a one liner can be used
mat = [list(map(int,input().split())) for i in range(row)]
Source: Stackoverflow.com