Lua Array shuffle not working - lua

Question

I was working on a script to randomize the data inside of my array but I get and error
that says
unexpected symbol near "#"
When I go to that line, and I remove the "#" I get
attempt to perform arithmetic on local `n' (a table value)
Here is my shuffle function
function shuffle(array)
local array = array
local n = #array
local j
local random = math.random
for i=n-1, 1, -1 do
j = random(i)
array[j],array[i] = array[i],array[j]
end
return array
end
and here is what I am trying to randomize
shuffle(new_players)
for name,character in pairs(new_players) do
if (character.inside == true and character.death == 0) then
local player = getPlayerByName(name, map_copy)
if (player ~= nil) then
addState(player)
break
end
end
end
Here is my array
new_players= { }
new_players[charName] = { death = 0, inside= true }
Any help? If i am doing something completely wrong?

Answer 1

1) Try change charName from string to a number.
2) For shuffle you can use this code:
function swap(array, index1, index2)
array[index1], array[index2] = array[index2], array[index1]
end
function shuffle(array)
local counter = #array
while counter > 1 do
local index = math.random(counter)
swap(array, index, counter)
counter = counter - 1
end
end

Answer 2

If your Lua version is < 5.1 then there is no # operator. Use table.getn instead:
local n = table.getn(array);
(Update) Note that your function, while it does shuffle the items around, it does not really shuffle all elements. Also since you reduce the range with each iteration, you will almost certainly swap the first 10% of your array around multiple times. Now swapping them multiple times is not bad by itself, but that you are, by comparison, almost never swapping the other elements is.
So one option to solve this would be to always use the same range for your random variable. And I would go even further and select two random indexes to swap:
function shuffle(array)
local n, random, j = table.getn(array), math.random
for i=1, n do
j,k = random(n), random(n)
array[j],array[k] = array[k],array[j]
end
return array
end
The other option would be to select random elements from the source array and put them into a new output array:
local rnd,trem,getn,ins = math.random,table.remove,table.getn,table.insert;
function shuffle(a)
local r = {};
while getn(a) > 0 do
ins(r, trem(a, rnd(getn(a))));
end
return r;
end