How to find neighbors of element in matrix in python?

Question

I need help with a function that's supposed to return all neighbors of element in a matrix, I can't use numpy because it's a project for school.

For example for given matrix:

m =  [ 11 12 13
       21 22 23
       31 32 33 ] 

I need get_neigbors(x,y) function that returns all of elements around the element m[x][y]. for example get_neighbors(1,1) is supposed to return [12, 21, 22] And please, no one liners.! Thanks.

Answer 1

You can use a list of dx,dy offsets from the position given and return values for which the relative position is within the matrix's index ranges.

def get_neighbours(m,x,y):
    rows, cols = range(len(m)),range(len(m[0]))
    offsets = [(-1,-1),(-1,0),(-1,1),(0,-1),(0,1),(1,-1),(1,0),(1,1)]
    result = []
    for dy,dx in offsets:
        ny, nx = y-1+dy, x-1+dx
        if ny in rows and nx in cols:
            result.append(m[ny][nx])
    return result

output:

m =  [ [11, 12, 13],
       [21, 22, 23],
       [31, 32, 33] ]

print(get_neighbours(m,1,1)) # [12, 12, 22]

Note that, Python indexes are zero-based but your example assumes that (1,1) is the top-left corner, so I subtracted 1 from the parameter values to get actual indexes in the matrix. You also need to pass the matrix as parameter to the function in order to access its content.