lua: comparing entries of tables in tables

Question

I need to duplicate each 'pos' from {CLOSED} into {PATH}, but in order of where they 'came_from' starting with 'target'. It's the last part of a pathfinding method. I've been unsuccessful turning my pseudo-code into lua code and need help doing so. I think it would be easiest for me to understand if someone could convert the pseudocode into code as there are a few underlying fundamentals at play here I'm confusing with eachother.

i.e. path={{x=33,y=44},{x=22,y=25},{x=0,y=0}}

start={x=0,y=0}
target={x=33,y=44}
CLOSED={
    {pos={x=33,y=44},came_from={x=22,y=25}},
    {pos={x=0,y=0},came_from={x=nil,y=nil}},
    {pos={x=22,y=25},came_from={x=0,y=0}}
}
PATH={}

--outline:
current=target

while current~=start do
    add(path,current)
--??    current=CLOSED[i].came_from[current]??
--outstanding steps:
--check current against each 
--CLOSED[i].pos
--if we have a match, 
--current=closed[i].came_from
--repeat
end

Answer 1

Tables can't be compared unless specifically assigned to eachother (i.e. {a}={b}). So you have to grab and compare the individual values of all the keys of same variable (i.e. x and y). The functions below can do that, returning true if they get a hit. Another more specific method would be to convert the x,y coordinates from 2d to 1d and compare the integers(so with an nxm matrix its x+m*y).

start={x=0,y=0}
target={x=33,y=44}
closed={
    {pos={x=33,y=44},came_from={x=22,y=25}},
    {pos={x=0,y=0},came_from={x=nil,y=nil}},
    {pos={x=22,y=25},came_from={x=0,y=0}}
}
path={}

--outline:
current=target
function subset(a,b)
    for k,v in pairs(a) do
  if b[k]~=v then return false end
    end
 return true
end
function equal(a,b)
 return subset(a,b) and subset(b,a)
end

while current.x~=start.x and current.y~=start.y do
    --check current against each 
    --closed[i].pos
    --if we have a match, 
    --current=closed[i].came_from
    --repeat
 add(path,current)
    for i=1,#closed do
        if equal(current,closed[i].pos) then
            current=closed[i].came_from
            break
        end
    end
end
add(path,start)


--expected path={{x=33,y=44},{x=22,y=25},{x=0,y=0}}
--check:
for k,v in pairs(path) do
    for k,v in pairs(v) do
    print(k.."="..tostr(v))
    end
end