Question

I have a 570 x 800 matrix with id values. What I would like to do if find the adjacent neighbors for each item. The max number of neighbors would be 8 unless the cell is along a boundary. In that case, there would be three neighbors. I want to append the neighbors to a list. I saw the posting for finding neighbors when each cell has x and y coordinates which was very helpful, but how would modify the code with no coordinates. The ids come in as a string which is fine because I use it as a key in a dictionary. Any help would be appreciated.

Answer 1

code with no coordinates? Do you mean like this:

XMAX = 800
YMAX = 570

NEIGHBOURS = [(-1, -1), (0, -1), (1, -1), (-1, 0), (1, 0), (-1, 1), (0, 1), (1, 1)]

matrix = range(XMAX * YMAX)

def all_neighbours(m):
    for i in xrange(len(m)):
        ns = []
        y, x = divmod(i, XMAX)
        for u, v in NEIGHBOURS:
            ux = u + x
            vy = v + y
            if 0 <= ux < XMAX and 0 <= vy < YMAX:
                ns.append(ux + vy * YMAX)
        yield i, ns

if __name__ == '__main__':

    for field, neighbours in all_neighbours(matrix):
        print field, neighbours