Lua game development, table seems to delete itself after each interation - list

Question

What I am trying to do is a little addon which would let me know how much time I have spent casting during combat in %,
function()
local spell, _, _, _, _, endTime = UnitCastingInfo("player")
-- getting information from the game itself whether im "Casting"
local inCombat = UnitAffectingCombat("player")
-- getting information form the game if combat is true (1) or not (nil)
local casting = {}
local sum = 0
if inCombat == 1 then
if spell then
table.insert(casting, 1)
else
table.insert(casting, 0)
end
else
for k in pairs (casting) do
casting [k] = nil
end
end
for i=1, #casting, 1 do
sum = sum + casting[i]
end
return( sum / #casting ) end
-- creating a list which adds 1 every frame I am casting and I am in combat,
-- or adds 0 every frame I'm not casting and I'm not in combat.
-- Then I sum all the numbers and divide it by the number of inputs to figure
-- out how much % I have spent "casting".
-- In case the combat condition is false, delete the list
For some reason these numbers don't add up at all, I only see "1" when both conditions are satisfied, or 0 if the combat condition is satisfied.
There might be some better approach I'm sure, but I am kind of new to lua and programming in general.

Answer 1

You say you're new to Lua, so I will attempt to explain in detail what is wrong and how it can be improved, so brace yourself for a long read.
I assume that your function will be called every frame/step/tick/whateveryouwanttocallit of your game. Since you set sum = 0 and casting = {} at the beginning of the function, this will be done every time the function is called. That's why you always get 0 or 1 in the end.
Upvalues to the rescue!
Lua has this nice thing called lexical scoping. I won't go into much detail, but the basic idea is: If a variable is accessible (in scope) when a function is defined, that function remembers that variable, no matter where it is called. For example:
local foo
do
local var = 10
foo = function() return var end
end
print(bar) -- nil
print(foo()) -- 10
You can also assign a new value to the variable and the next time you call the function, it will still have that new value. For example, here's a simple counter function:
local counter
do
count = 0
counter = function() count = count + 1; return count; end
end
print(counter()) -- 1
print(counter()) -- 2
-- etc.
Applying that to your situation, what are the values that need to persist from one call to the next?
Number of ticks spent in combat
Number of ticks spent casting
Define those two values outside of your function, and increment / read / reset them as needed; it will persist between repeated calls to your function.
Things to keep in mind:
You need to reset those counters when the player is no longer casting and/or in combat, or they will just continue where they left off.
casting doesn't need to be a table. Tables are slow compared to integers, even if you reuse them. If you need to count stuff, a number is more than enough. Just make casting = 0 when not in combat and increase it by 1 when in combat.

Answer 2

Thank you for feedback everyone, in the end after your suggestions and some research my code looks like this and works great:
function()
local spell, _, _, _, startTime, endTime, _, _, _ = UnitCastingInfo("player")
local inCombat = UnitAffectingCombat("player")
local inLockdown = InCombatLockdown()
local _, duration, _, _ = GetSpellCooldown("Fireball")
casting = casting or {}
local sum = 0
if inCombat == 1 or inLockdown == 1 then
if spell or duration ~= 0 then
casting[#casting+1] = 1
elseif spell == nil or duration == 0 then
casting[#casting+1] = 0
end
else
local next = next
local k = next(casting)
while k ~= nil do
casting[k] = nil
k = next(casting, k)
end
end
for i=1, #casting, 1 do
sum = sum + casting[i]
end
return(("%.1f"):format( (sum / #casting)*100 ).. "%%") end
what i noticed is there was a problem with reseting the table in the original code:
for k in pairs (casting) do
casting [k] = nil
it seemed like either some zeros stayed there, or the table size didnt "shrink" i dont know.
Maybe intereger would be faster then a table, but honestly i dont see any performance issues even when the table gets ridicolously big (5 min, 60 fps, thats 18k inputs) also for the sake of learning a new language its better to do it harder way in my opinion
Regards