wrapping around slices in Python / numpy

Question

I have a numpy array, and I want to get the \"neighbourhood\" of the i\'th point. Usually the arrays I\'m using are two-dimensional, but the following 1D example illustrates

Answer 1

You can use the np.pad routine like this:

A = np.array([0,10,20,30,40,50,60,70,80,90])
A = np.pad(A, 2, 'wrap')
print(A)
[80, 90,  0, 10, 20, 30, 40, 50, 60, 70, 80, 90,  0, 10]

Say you have a neighbor function:

def nbf(arr):
    return sum(arr)

To apply the neighbor function to every 5 you need to be careful about your start and end indices (in the range(...) command) and the relative slice you take from A.

B = [nbf(A[i-2:i+3]) for i in range(2,12)]
print(B)
[200, 150, 100, 150, 200, 250, 300, 350, 300, 250]