Radix sort not working in Lua - algorithm

Question

Firstly I should mention I've not been coding very long at all, although that much is probably obvious from my code :P
I'm having two problems, firstly the sort isn't functioning correctly but does sort the numbers by their length. Any help here would be appreciated.
Secondly it's changing both the table it grabs and the table it returns (not sure why). How do I prevent it changing the table it grabs?
I'd prefer if people didn't post a fully optisimised premade code as I'm not going to learn or understand anything that way.
function radix_sort(x)
pass, bucket, maxstring = 0, x, 2
while true do
pass = pass + 1
queue = {}
for n=#bucket,1,-1 do
key_length = string.len(bucket[n])
key = bucket[n]
if pass == 1 and key_length > maxstring then
maxstring = key_length
end
if key_length == pass then
pool = string.sub(key, 1,1)
if queue[pool + 1] == nil then
queue[pool + 1] = {}
end
table.insert(queue[pool + 1], key)
table.remove(bucket, n)
end
end
for k,v in pairs(queue) do
for n=1,#v do
table.insert(bucket, v[n])
end
end
if pass == maxstring then
break
end
end
return bucket
end

Answer 1

There's a lot of changes I made to get this working, so hopefully you can look through and pickup on them. I tried to comment as best I could.
function radix_sort(x)
pass, maxstring = 0, 0
-- to avoid overwriting x, copy into bucket like this
-- it also gives the chance to init maxstring
bucket={}
for n=1,#x,1 do
-- since we can, convert all entries to strings for string functions below
bucket[n]=tostring(x[n])
key_length = string.len(bucket[n])
if key_length > maxstring then
maxstring = key_length
end
end
-- not a fan of "while true ... break" when we can set a condition here
while pass <= maxstring do
pass = pass + 1
-- init both queue and all queue entries so ipairs doesn't skip anything below
queue = {}
for n=1,10,1 do
queue[n] = {}
end
-- go through bucket entries in order for an LSD radix sort
for n=1,#bucket,1 do
key_length = string.len(bucket[n])
key = bucket[n]
-- for string.sub, start at end of string (LSD sort) with -pass
if key_length >= pass then
pool = tonumber(string.sub(key, pass*-1, pass*-1))
else
pool = 0
end
-- add to appropriate queue, but no need to remove from bucket, reset it below
table.insert(queue[pool + 1], key)
end
-- empty out the bucket and reset, use ipairs to call queues in order
bucket={}
for k,v in ipairs(queue) do
for n=1,#v do
table.insert(bucket, v[n])
end
end
end
return bucket
end
Here's a test run:
> input={55,2,123,1,42,9999,6,666,999,543,13}
> output=radix_sort(input)
> for k,v in pairs(output) do
> print (k , " = " , v)
> end
1 = 1
2 = 2
3 = 6
4 = 13
5 = 42
6 = 55
7 = 123
8 = 543
9 = 666
10 = 999
11 = 9999

Answer 2

pool = string.sub(key, 1,1)
always looks at the first character; perhaps you meant string.sub(key, pass, 1)