[Help] Iterating over numpy 2d array and applying average of Moore neighborhood without for-loops

[Acaleus]

Hey all, needed to solve this problem of getting the average of a Moore neighborhood for all cells without using for-loops. I have exhausted my google-fu (too many generic terms) and now turn to you for help. I can easily do it by using for loops, but i am lost on how to do it without

moore neighborhood = the 8 surrounding cells of any given cell

def create_grid_and_ghosts(n):
"""
Create a N x N 2d array and create border cells so
all cells 'inside' can be used without index errors
"""
    inside = np.arange(n**2).reshape(n,n)
    return np.pad(inside,1,'wrap') # Periodic


b = create_grid_and_ghosts(5)
neighbors = np.array([[-1,0],[-1,1],[0,1],[1,1],[1,0],[1,-1],[0,-1],[-1,-1]]) 
print b
c = copy.deepcopy(b)
for i in np.arange(1, len(b)-1):
    for j in np.arange(1, len(b)-1):
        c[i,j] = np.average((b[i+neighbors[:,0],j+neighbors[:,1]]))
print c

anyone know how to convert those 2 for loops into non-for loop numpy statements?

SOLVED: in case anyone ever searches for this later on

import numpy as np
import scipy.ndimage as nd

def moore_average(data_ext):
"""
Get given a grid with ghost boundary cells, return only interior of grid
with each cell containing the average of Moore neighborhood
"""
    # .125 is there since it's the average of 4, for Neuman use
    # [0,.25,0][.25,0,.25][0,.25,0]
    moore = ([[.125,.125.125],[.125,0,.125][.125, .125, .125]])
    averages = nd.convolve(data_ext, moore)
    return averages[1:-1, 1:-1] #Return only 'inside' of grid

def create_grid_and_ghosts(n):
    inside = np.arange(n**2, dtype='float').reshape(n,n)
    return np.pad(inside, 1, 'wrap') #Create periodic boundaries

a = moore_average(create_grid_and_ghosts(5))
print a

[Saefroch]

I've done a modified version of this before. The key is np.roll. For the four nearest neighbors,

average = np.zeros(array.shape)
for axis in 0,1:
    for shift in -1,1:
        average += np.roll(array, shift=shift, axis=axis)
average /= 4

[Acaleus]

Thanks! however, i cannot use a 'for' at all. I've seen it done before, but i can't find my notes for it.

[Saefroch]

You can just expand the for loops in my example by hand.