How to rotate an array in Python?

Question

I'm trying to rotate an array in Python. I've read the following post Python Array Rotation

Where I found this little snippet of code

arr = arr[numOfRotations:]+arr[:numOfRotations]

I've tried to put this into the following function:

def solution(A, K):
    A = A[K:] + A[:K]
    print(A)
    return A

Where A is my array and K is the number of rotations. Only I get the following error, ValueError: operands could not be broadcast together with shapes (3,) (2,).

I don't understand where I'm going wrong? Ideally I a solution that can solve this without using any Numpy inbuilt short cuts functions.

Cheers

Edit: This is the full program

A = np.array([1, 2, 3, 4, 5])

def solution(A, K):
    A = A[K:]+A[:K]
    print(A)
    return A

solution(A, 2)

Could you show us how you are calling your method ? The code you provided work well for me using solution([1,2,3], 1) — gcourtet
– gcourtet, Commented Oct 2, 2020 at 8:10
Really these don't work??? Worked for me with solution([1,2,3],1) in test — avarice
– avarice, Commented Oct 2, 2020 at 8:10
So when I call it the same way you two did it works fine, but this method provides a list as the argument and not an array. Which seems to be the issue — Mike5298
– Mike5298, Commented Oct 2, 2020 at 8:28

Ajay Verma · Accepted Answer · 2020-10-02 08:37:09Z

2

You need to use np.concatenate((A[K:],A[:K])) if A is an array, you function works when A is list

Lest try to look at from your example

A = np.array([1, 2, 3, 4, 5])
K = 2
print(A[K:])
print(A[:K])

Will give you [3 4 5] and [1 2] . in your code you are trying to add them using + sign. Since the these two values are of different shapes you cant add them, hence you will get ValueError: operands could not be broadcast together with shapes (3,) (2,)

The correct implementation for an array will be

import numpy as np
A = np.array([1, 2, 3, 4, 5])

def solution(A, K):
    A = np.concatenate((A[K:],A[:K]))
    print(A)
    return A

edited Oct 2, 2020 at 8:37

answered Oct 2, 2020 at 8:30

Ajay Verma

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