Multidimensional array by user input in python

Question

I used Jupyter notebook, I am new to Python, I try to fetch value from user in multidimensional array how I do that? I write a little code, after put first value I get error that I don't understand

Error:

Traceback (most recent call last)
 <ipython-input-64-4d8986a5e412> in <module>
 5 for i in range(lengthrow):
 6 for j in range(lengthcol):
 ----> 7 arr[i][j]=int(input("enter value"))
 8 print(arr)

IndexError: index 0 is out of bounds for axis 0 with size 0

code:

from numpy import*
arr = array([[],[]])
lengthrow=int(input("enter array row length"))
lengthcol=int(input("enter array col length"))
for i in range(lengthrow):
 for j in range(lengthcol):
 arr[i][j]=int(input("enter value"))
print(arr)

• hpaulj: You made arr a (2,0) shape array. arr[0] is a (0,) shape array. Trying to index that with [0] produces the error.

Answer 1

I took @Austin great answer and made some little changes:

import numpy as np
n_rows = int(input("Enter number of rows: "))
n_cols = int(input("Enter number of columns: "))
arr = [[int(input("Enter value for {}. row and {}. column: ".format(r + 1, c + 1))) for c in range(n_cols)] for r in range(n_rows)]
print(np.array(arr))

The output is:

Enter number of rows: 2
Enter number of columns: 3
Enter value for 1. row and 1. column: 1
Enter value for 1. row and 2. column: 2
Enter value for 1. row and 3. column: 3
Enter value for 2. row and 1. column: 4
Enter value for 2. row and 2. column: 5
Enter value for 2. row and 3. column: 6
[[1 2 3]
 [4 5 6]]

You got an exception, because you initialized an empty array and used invalid indices. With this answer you generate the array after you have entered the users input.

---

Here is the long version of the one-liner (arr = [[...) which gives you the same result:

outer_arr = []
for r in range(n_rows):
 inner_arr = []
 for c in range(n_cols):
 num = int(input("Enter value for {}. row and {}. column: ".format(r + 1, c + 1)))
 inner_arr.append(num)
 outer_arr.append(inner_arr)
print(np.array(outer_arr))

• DevWebTk: Thanks Darius Morawec, this method as also great actually I need this output thanks a lot.Can you suggest some reference to learn two dimensional array I need to deeply learn about it.Thank you :)
• Darius: Sure, multidimensional arrays are matrices in linear algebra, which allows you do to powerful operations. Here are some introductions: #1, #2, #3 and #4.
• DevWebTk: Again Thanks a lot @Darius Morawiec :)
• DevWebTk: Can you explain this line [[int(input("Enter value for {}. row and {}. column: ".format(r + 1, c + 1))) for c in range(n_cols)] for r in range(n_rows)] i don't really understand how flow of for loop
• Darius: @ToufikKhan Sure, I edited the answer and added a longer version of the same code. We use two for loops to create a list of lists which we convert to a two-dimensional array.

Answer 2

You can use a list-comprehension here as the final result is a list of lists:

lengthrow = int(input("enter array row length: "))
lengthcol = int(input("enter array col length: "))
arr = [[int(input("enter value: ")) for _ in range(lengthcol)] for _ in range(lengthrow)]
print(arr)

Problem with your code:

arr = array([[],[]])
print(arr.shape)
# (2, 0)

That means you have a size 0 column in array, so when you do arr[0][0], for example, it throws error.

Answer 3

The problem is the shape of the initial array:

In [1]: arr = np.array([[], []])
In [2]: arr
Out[2]: array([], shape=(2, 0), dtype=float64)
In [3]: arr[0]
Out[3]: array([], dtype=float64)
In [4]: arr[0][0]
... 
IndexError: index 0 is out of bounds for axis 0 with size 0

Think of this array as 2 rows, 0 columns. You can't reference a non-existent column. And, in contrast to some other languages, you can't grow an array simply by referencing a new index. Once created the size is fixed.

While others have shown nice list comprehension approaches, I'll show how to use your approach correctly:

In [8]: lengthrow, lengthcol = 2,3 # or user input
In [9]: arr = np.zeros((lengthrow, lengthcol), dtype=int) # large enough array
In [10]: arr
Out[10]: 
array([[0, 0, 0],
 [0, 0, 0]])
In [11]: for i in range(2):
 ...: for j in range(3):
 ...: arr[i,j] = int(input(f'{i},{j}:'))
 ...: 
0,0:0
0,1:1
0,2:2
1,0:3
1,1:4
1,2:5
In [12]: arr
Out[12]: 
array([[0, 1, 2],
 [3, 4, 5]])

• DevWebTk: Thanks for your valuable replay, this salutation is really good. once again thank you :)
• DevWebTk: np.array() function convert the list to numpy array