Question about for loops

[SquareFish]

I have this code here for removing a bunch of zombies in the zombies table, each of the values in zombies is a individual zombie table:
for i,z in ipairs(zombies) do
zombies [ i ] = nil (1)
z = nil (2)
end

My question is, why does line (1) work and line (2) doesn't? When I try line 2 nothing happens. So far I have the understanding that using z is like using a for each loop, and it points to the first value/object in the table, then the next, and so on. I was just wondering why z = nil doesn't work as opposed to zombies = nil. My best guess is the fact that it has to do with z not wanting to be null because it has another index in the loop to go on to or something like that

Thanks a lot guys, I never use for each loops in java so they're pretty confusing to me with lua

[darkfrei]

Wrong:

Code: Select all

for i,z in ipairs(zombies) do
  zombies = nil -- the table zombies does not exist anymore 
  z = nil -- local / global z does not exist
end

Good:

Code: Select all

for i = #zombies, 1, -1 do -- backwards from last to first
  zombies[i] = nil
end

Also good:

Code: Select all

for i, z in ipairs(zombies) do
  zombies[i] = zombies[#zombies] -- the i-th zombie is gone, now the i-th zombie is exactly-same as last
  zombies[#zombies] = nil -- remove the last
end

[SquareFish]

Thanks, I realized that the forum text editor removed the [ i ] that I added after the zombies on line one, I edited my post to add it in. Thanks a lot though, both these options make sense. I've had a lot of trouble with removing objects in a list in the past and for some reason it never occurred to me to just iterate backwards.

[Andlac028]

Thanks, I realized that the forum text editor removed the [ i ]

Thats what [ code ] [/ code] tags are for (without spaces in [])

[darkfrei]

Extra question: what happens?

Code: Select all

for i = 1, 3 do
  i = 4
  print (i)
end

[pgimeno]

Here's the OP's code again surrounded with proper [code]...[/code] tags:

Code: Select all

for i,z in ipairs(zombies) do
        zombies[i] = nil (1)
        z = nil (2)
end

The answer to understand what's going on in numeric loops and predict the behaviour is in the manual's section 2.4.5.

More precisely, a for statement like

Code: Select all

     for v = e1, e2, e3 do block end

is equivalent to the code:

Code: Select all

     do
       local var, limit, step = tonumber(e1), tonumber(e2), tonumber(e3)
       if not (var and limit and step) then error() end
       while (step > 0 and var <= limit) or (step <= 0 and var >= limit) do
         local v = var
         block
         var = var + step
       end
     end

[...]

• var, limit, and step are invisible variables. The names shown here are for explanatory purposes only.

Note that altering v (the loop variable) is not going to influence the stop condition because it's stored in a new local with the same name after being assigned from var.

(Edited after realizing that I misunderstood a few things)