Get Random Value from Table

[bane_]

I use this mini-function to get random values from tables:

function tablerandom(tbl)
	local keys = {}
	for k in pairs(tbl) do
		table.insert(keys, k)
	end
	local randIndex = math.random(#keys) -- this is line 23
	local randKey = keys[randIndex]
	return tbl[randKey]
end

It's been working quite well for me, but now that I'm doing some AI-tuning (holy crap, how this **** is hard) I'm getting this error:

[32015.632] Runtime Error: C:\Users\bane_\Documents\My Games\Sid Meier's Civilization 5\MODS\Crane Clan (v 1)\Lua\Lib\DomotaiUtils.lua:23: bad argument #1 to 'random' (interval is empty)

It happens when it gets a nil interval (as explicitly told by the log ), BUT I wanna know why this is the first time I'm getting those.
I was using table.insert to put in IDs from workers, like this:

Spoiler :

for pUnit in pPlayer:Units() do
	if pUnit:GetUnitType() == GameInfoTypes["UNIT_KAKITA_ARTISAN"] and pUnit:GetPlot():GetOwner() == iPlayer then
		table.insert(CraneAvWorkers, pUnit:GetID())
		bCraneAvWorkers = true
		print("A Crane worker was inserted into the 'CraneAvWorkers' table")
	elseif pUnit:GetUnitType() == GameInfoTypes["UNIT_KAKITA_ARTISAN"] and not pUnit:IsBusy() and pUnit:GetPlot():GetOwner() ~= iPlayer and pUnit:GetPlot():GetOwner() >= 0 then
		local pPlot = pUnit:GetPlot()
		local iUnit = pUnit:GetID()
		LookForSuitableGardens(iUnit, pPlot, false)
		print("Looking for suitable place for a garden with boolean as 'false'.")
	end
end

So I suspect the problem is that the ID from the Worker will not be contiguously, leaving small breaches between one number and the other. I imagine using CraneAvWorkers[iUnitID] (with iUnitID defined, obviously) will result in the same eventual errors.

Any ideas how to fix this?

 

[whoward69]

The problem is almost certainly being caused by calling the tablerandom function with an empty tbl parameter, ie tablerandom({}), which will possibly happen when the player has no workers

 

[bane_]

But I'm getting the "A Crane worker was inserted into the 'CraneAvWorkers' table" print. Shouldn't there be an error with the prior 'table.insert' then?

 

[Bobert13]

function tablerandom(tbl)

	if tbl == nil then
		print("OHNOES! a nil value!")
		return 9000
	end

	local keys = {}
	for k in pairs(tbl) do
		table.insert(keys, k)
	end
	local randIndex = math.random(#keys) -- this is line 23
	local randKey = keys[randIndex]
	return tbl[randKey]
end

 

[whoward69]

If tbl was nil, you'd get a "bad argument #1 to 'pairs' (table expected, got nil)" error, the problem is being caused by tbl being empty, ie {}, and doing math.random(0), which will cause the "bad argument #1 to 'random' (interval is empty)" error

 

[whoward69]

The code in the spoiler does not call the tablerandom() function, so without the full mod, it is impossible to say under what circumstances you are effectively calling tablerandom({})

 

[LeeS]

DarkScythe put me onto this a while back, which is often useful to me for trouble-shooting little bits of lua behavior. lua demo page

You could dummy up some conditions and see which ones are going to cause a similar error, so you'll at least know which possible conditions you need to take action within your lua to avoid.

doing this:

function tablerandom(tbl)

	if tbl == nil then
		print("OHNOES! a nil value!")
		return 9000
	end

	local keys = {}
	for k in pairs(tbl) do
		table.insert(keys, k)
	end
	local randIndex = math.random(#keys) -- this is line 23
	local randKey = keys[randIndex]
	return tbl[randKey]
end
joe = {}
tablerandom(joe)

in that demo program gives me this error:

input:12: bad argument #1 to 'random' (interval is empty)

[edit]I also was under the impression that the keys (k) had to be numerical and sequential in order for #keys to return anything except a nil value.

 

[whoward69]

[edit]I also was under the impression that the keys (k) had to be numerical and sequential in order for #keys to return anything except a nil value.

keys will be numerical and sequential, because it has been constructed from table.insert() calls

if tbl is {"a"="xyz", "f"="lmn", "z"=12}
then keys[1]="a", keys[2]="f" and keys[3]="z", so #keys will be 3

exactly what is required

however if tbl = {}
then keys will be empty, so #keys will be 0, so math.random(0) will throw the error being reported

 

[LeeS]

table.insert(keys, k)

not sure how I overlooked that part.

Nice workaround for the table length issue, BTW, bane_. I may have to steal borrow this at some future point.

 

[bane_]

@Bobert13: The print won't help much, unfortunately, since I already have a confirmation when things go wrong. I need to find a way for them to NOT go wrong. Also, why return 9000? Didn't get that part.

so without the full mod

You are right. I should've posted it all at first. Here it is:

-AIHelper.lua

Spoiler :

for i = 0, GameDefines.MAX_MAJOR_CIVS - 1, 1 do
	print("Checking now if anyone is friend with the Crane. Only going forward if that's true and CraneAvWorkers isn't nil.")
	if Players[i]:IsDoF(iPlayer) and bCraneAvWorkers then
		for pCity in Players[i]:Cities() do
[B]			local iCraneWorker = tablerandom(CraneAvWorkers)[/B]
			local bCraneWorkerUsed = IsWorkerUsed(iCraneWorker)
			print("Checking if the Worker is already used. Is it?" ..tostring(bCraneWorkerUsed))
			[B]while bCraneWorkerUsed do
				print("It was true. Trying again...")
				iCraneWorker = tablerandom(CraneAvWorkers)
				bCraneWorkerUsed = IsWorkerUsed(iCraneWorker)
				print("Second Check: Is the Worker already used?" ..tostring(bCraneWorkerUsed))
			end[/B]
			table.insert(CraneAvWorkers, pUnit:GetID())
			local pUnit = pPlayer:GetUnitByID(iCraneWorker)
			local pPlot = Map.GetPlot(pCity:GetX(), pCity:GetY())
			for idX = -2, 2, 1 do
				for idY = -2, 2, 1 do
					local pTargetPlot = Map.PlotXYWithRangeCheck(pPlot:GetX(), pPlot:GetY(), idX, idY, 2)
					if pTargetPlot and pTargetPlot:GetOwner() == i and pTargetPlot:CanHaveImprovement(GameInfoTypes["IMPROVEMENT_FANTASTIC_GARDENS"], NO_TEAM) then
						pUnit:PushMission(MissionTypes.MISSION_MOVE_TO, pTargetPlot:GetX(), pTargetPlot:GetY(), 0, 0, 1)
						LookForSuitableGardens(iUnit, pPlot, true)
						print("Looking for suitable place for a garden with boolean as 'true'.")
						bBreakReal = true
						break
					end
					if bBreakReal then
						break
					end
				end
				if bBreakReal then
					bBreakReal = false
					break
				end
			end
		end
	end
end

-DomotaiUtils.lua

Spoiler :

iCraneClan = 0

function GetCranePlayer()
	for i = 0, GameDefines.MAX_MAJOR_CIVS - 1, 1 do
		Players[i]:SetNumFreePolicies(1)
		Players[i]:SetNumFreePolicies(0)
		if Players[i]:GetCivilizationType() == GameInfoTypes["CIVILIZATION_CRANE_CLAN"] then
			iCraneClan = i
			print("Crane Clan ID: " ..iCraneClan)
		end
	end
end

function GetRandom(iMin, iMax)
	return Map.Rand((iMax + 1) - iMin, "") + iMin
end

[B]function tablerandom(tbl)
	local keys = {}
	for k in pairs(tbl) do
		table.insert(keys, k)
	end
	local randIndex = math.random(#keys)
	local randKey = keys[randIndex]
	return tbl[randKey]
end[/B]

[...]

Nice workaround for the table length issue, BTW, bane_. I may have to steal borrow this at some future point.

Are you kidding? It's property of every one. It's already yours as well.