How do I reference adjacent elements in a matrix?

Question

I am trying to make some code so that a single element a matrix can reference elements adjacent to it. Sort of like how you can only move game pieces to spaces adjacent. For example, I want to be able to say something like:

if x matrix element is adjacent to y element:
     y_element_adjacent = True

I want to know how to accomplish the 'is adjacent' portion of this.

EDIT: I have tried making a list and assigning each element a number. So in a 100 element list (or a 10x10 game board), space 1x1 would be the 0th element and space 1x3 would be the 2nd element... Like this:

1, 2, 3, 4, 5, 6, 7, 8, 9, 10

11, 12, 13, 14, 15, 16, 17, 18, 19, 20

However, the problem with this is that if the x element was 10, my code would take + 1 to find an adjacent space, and 11 is NOT adjacent. I then realized that lists are not the correct way to do this and matrices would be a the way to go. I'm just a little confused on how I can use them differently than lists.

Any help is appreciated! Thanks.

There are many, many ways to do this, depending on how your code is organized. Can you be more specific about what you have and - more importantly - what you've tried yourself before asking this question? — TigerhawkT3, Jul 20 '16 at 23:43
Just take all 4 neighbors (+1 and -1 index for x, the same for y -> 2*2 combs; or 8 if diagonals are *adjacent*). But before indexing, check if within bounds (x+1 < x_length; x-1 >= 0; y+1 < y_length, y-1 >= 0) — sascha, Jul 20 '16 at 23:45
Thanks for the comments. Edited with my original thought process. — Jerfy, Jul 21 '16 at 15:17

score 1 · Accepted Answer · edited May 23 '17 at 10:28

Here's a simple way to obtain indices of all adjacent elements.

from itertools import product, starmap

x, y = (x_coordinate, y_coordinate) # matrix values here
cells = starmap(lambda a,b: (x+a, y+b), product((0,-1,+1), (0,-1,+1)))

For an input of x,y = (1,1), this returns (list(cells)[1:]) containing [(1, 0), (1, 2), (0, 1), (0, 0), (0, 2), (2, 1), (2, 0), (2, 2)].

Such an implementation might be of interest in your particular scenario (determining to which places a certain game piece may move). If you want to include border checking, you might try

X = max_board_X
Y = max_board_Y    
neighbors = lambda x, y : [(x2, y2) for x2 in range(x-1, x+2)
                                   for y2 in range(y-1, y+2)
                                   if (-1 < x <= X and
                                       -1 < y <= Y and
                                       (x != x2 or y != y2) and
                                       (0 <= x2 <= X) and
                                       (0 <= y2 <= Y))]

Other solutions (and sources for these) may be found here: Determining neighbours of cell two dimensional list

Thank you! This helps out quite a bit! – Jerfy Jul 26 '16 at 18:53 — Jerfy, Jul 26 '16 at 18:53

How do I reference adjacent elements in a matrix?

1 Answers1