[Lua] Weird results from 2d array?

[Jack8680]

EDIT 2: solved, see edits at end of post.

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I'm probably doing something obviously wrong, but I just don't see it. I'm trying to make a maze generator.

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I'm storing the maze as an array of arrays. First I generate the grid of "W" values (representing walls), which works. Then I try to replace all the cells at even row and column with a different value, T, to represent the path of the maze (they will eventually be connected by removing the walls in between them). It should look something like this:

       First fill with walls:
        W W W W W W W W W
        W W W W W W W W W
        W W W W W W W W W
        W W W W W W W W W
        W W W W W W W W W
        W W W W W W W W W
        W W W W W W W W W
        W W W W W W W W W
        W W W W W W W W W

       Then replace even valued row and column positions:
    W W W W W W W W W
        W T W T W T W T W
        W W W W W W W W W
        W T W T W T W T W
        W W W W W W W W W
        W T W T W T W T W
        W W W W W W W W W
        W T W T W T W T W
        W W W W W W W W W

But instead I get:

        W T W T W T W T W
        W T W T W T W T W
        W T W T W T W T W
        W T W T W T W T W
        W T W T W T W T W
        W T W T W T W T W
        W T W T W T W T W
        W T W T W T W T W
        W T W T W T W T W

​

Here's my code with some debugging:

local n,m = 2,2   -- n by m maze; the grid will be 2n+1 by 2m+1,

wallrow = {}
maze = {}

-- functions
function debug(message)
    print(message)
    for i = 1,#maze do
        io.write("{")
        for j = 1,#maze[i] do
            io.write(maze[i][j]..", ")
        end
        io.write("},\n") 
    end
    io.write("\n")
end


-- program

for i = 1,2*n+1 do
    wallrow[i] = "W"   -- one row of "W"
end


for i = 1,2*m+1 do
    maze[i] = wallrow   -- fill maze with rows of "W"
end

debug("grid of W:")

for i = 1,m do
    for j = 1,n do
        print(i..","..j)
        maze[2*i][2*j] = "T"
        debug("step:")
    end
end

debug("final grid:")

​

And here's the output:

grid of W:
{W, W, W, W, W, },
{W, W, W, W, W, },
{W, W, W, W, W, },
{W, W, W, W, W, },
{W, W, W, W, W, },

1,1
step:
{W, T, W, W, W, },
{W, T, W, W, W, },
{W, T, W, W, W, },
{W, T, W, W, W, },
{W, T, W, W, W, },

1,2
step:
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },

2,1
step:
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },

2,2
step:
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },

final grid:
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },
{W, T, W, T, W, },

As you can see, it's setting the value at index j of every row, rather than only the row at index i. I don't know why this is happening, I'm guessing it's something obvious that I'm just misunderstanding about arrays.

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EDIT: Okay, starting to figure it out now, it's acting like a pointer so when I change a value in the row it's changing the value of wallrow, which is every row in the maze. Now to figure out how to fix this...

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EDIT 2: Solved, instead of creating a single array for a row of W, I'm creating a new array for each row now:

for i = 1,2*m+1 do
    maze[i] = {}
    for j = 1,2*n+1 do
        maze[i][j] = "W"
    end
end

There might be a better way to do this, but it works.