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loop through numpy array produces typerror output : only integer scalar arrays can be converted to a scalar index

February 14, 2022

Say I have the following array a and subset 2×2 matrices from it:

import numpy as np
np.random.seed(0)

a = np.random.randint(9,size=(3,2,2))

for i in range(a.shape[0]):
    m = a[i]
    print(type(m))
    print(m)

<class 'numpy.ndarray'>
[[5 0]
 [3 3]]
<class 'numpy.ndarray'>
[[7 3]
 [5 2]]
<class 'numpy.ndarray'>
[[4 7]
 [6 8]]

Now if I want to loop through each of the matrices I get an error:

for i in range(a.shape[0]):
    m = a[i]
    for j in range(m):
        print(j)

TypeError: only integer scalar arrays can be converted to a scalar index

Why is that ? Can’t really debug this typerror.

>Solution :

You are trying to take the range of the matrix m, which doesn’t exist and thus the error. Instead, you should take the range of its shape[0] as you did in the first line for matrix a.

If you want to loop into each position of each matrix, then

import numpy as np
np.random.seed(0)

a = np.random.randint(9,size=(3,2,2))

for i in range(a.shape[0]):
    m = a[i]
    print(type(m))
    print(m)
    
for i in range(a.shape[0]):
    m = a[i]
    print("---")
    for x in range(m.shape[0]):
        for y in range(m.shape[1]):
            print(m[x,y])