Listing adjacent cells

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

Assuming that what you're trying to do is construct an eight-connected grid on the matrix, and that the position of item in the the matrix defines an x- and y- co-ordinate, you can use something like this:

def eight_connected_neighbours( xmax, ymax, x, y ):
    """The x- and y- components for a single cell in an eight connected grid

    Parameters
    ----------
    xmax : int
        The width of the grid

    ymax: int
        The height of the grid

    x : int
        The x- position of cell to find neighbours of

    y : int 
        The y- position of cell to find neighbours of

    Returns
    -------
    results : list of tuple
        A list of (x, y) indices for the neighbours    
    """
    results = []
    for dx in [-1,0,1]:
        for dy in [-1,0,1]:
            newx = x+dx
            newy = y+dy
            if (dx == 0 and dy == 0):
                continue
            if (newx>=0 and newx<xmax and newy >=0 and newy<ymax):
                results.append( (newx, newy) )
    return results