Attempt to index field ? (a nil value)

Question

I am writing a small RPG game engine with Lua/love2d, and I need to parse a file to a 2d array, but it don't work, and I am getting errors...

main.lua :

local fmap = love.filesystem.read("map.txt")
map = {}
for c in fmap:gmatch(".") do
    if c == "\n" then
        y = 0
        x = x + 1
    else
        map[x][y] = c -- this won't work
        y = y + 1
    end
end

map.txt :

6777633333
6558633333
6555614133
7757711112
2111111112
2111111112
2222222222

Answer 1

You can't use multi-dimensional array like this. See Matrices and Multi-Dimensional Arrays

You can transform your code like this :

local fmap = love.filesystem.read("map.txt")
map = {}
x = 0
y = 0
map[x] = {}
for c in fmap:gmatch(".") do
    if c == "\n" then
        y = 0
        x = x + 1
        map[x] = {}
    else
        map[x][y] = c -- this won't work
        y = y + 1
    end
end

Answer 2

I know that this has already been answered, but you'd probably find my (in progress) tile tutorial useful. The strings section deals with exactly the issue you are having.