[Lua] A small introduction to tables

[Dynashock]

[Disclaimer]: This guide's written with in mind that you have at least a basic knowledge of Lua.
Update! Spawning example has been added.

Intro
I am writing this (small) introduction to tables, because at a certain point I felt I had 'mastered' the Lua used of WoW scripting, however I couldn't be any more wrong. Lua at MMOwned isn't very complex, and it only covers certain (basic) aspects of Lua scripting, in terms of guides and releases (besides some exceptions). Lua is far stronger than that and is capable at more than you'd think, especially in use with the GuaEngine (or any 'upgraded' engine). This guide will cover the basic aspects of tables and how to use them, I hope you'll enjoy reading it and may it be of any use to you.


Tables - basics
What are tables? See it as a sort of closet with various drawers. In each drawer you can store something. But together they are part of a much greater whole. In our case of tables; a table is the closet in which you store your information in. It's not like a 'variable' though, which can only contain a single piece of information, because a table has 'drawers' which allows a table to store much more information, each apart of each other, while they all can still be called by the table's name. The information gets stored in an organised way in the drawers assigned to keys or indexes.

Example:

The variable  'pie' could contain 'cherrypie'. 
		The table 'pie' could contain 'cherrypie', 'applepie', 'blueberrypie'.

Syntax and tables
I'll be covering the following stuff:

Creating a table:
- table
- 'dictionary'

Basic syntaxes of a table:
- table.insert
- table.remove
- for k,v in pairs(table) do

Creating a table
Table
Creating a table is very easy and are created by the table constructers { and }. It's the same how you would create a variable instead you put the information between { } and each bit of information is seperated by a comma. A piece of information is also referred to as a value. If you want to store a string you will have to use " and ", else it might try to store a table/variable instead. Numbers do not require " ". The Lua engine will automatically assign an index to each 'drawer'. Note: you can also of course store numbers, variables, tables and even functions in a table! You can show what's in a table with tablename[index/key].

Example:

pie = {"cherrypie", "applepie", "blueberrypie"}
		In this case the indexes of cherrypie would be 1, applepie would have 2, and blueberrypie 3.
		Thus pie[2] = applepie.

Dictionary
A dictionary is more or less the same as a table however it allows you to give a name to each 'drawer' instead of an index number. You create one the same way you'd create a table (thus with {""}) but this time you define each name like NameOfDrawer = "1". An example to clarify:

Example:

deliciousness = {pie = "blueberrypie", cake = "chocolatecake"}
		This will store the value blueberrypie in the drawer with the key value 'pie' and the value chocolatecake in the drawer with the key value 'chocolatecake'. 
Thus deliciousness[cake] = chocolatecake.

Basic syntaxes of a table
Table.insert(table, position, value)
Position is not neccessary, if you won't provide it Lua will put the value as the last one in the row.

Example:

pie = {"cherrypie", "applepie", "blueberrypie"} 	-- Creating the table.
		table.insert(pie, 2, "blackberrypie")		-- Inserting blackberrypie at index number 2 in the table pie.
		The result of this would be that blackberrypie will now have the 2 as index which means that applepie will now have 3 as index.

Table.remove(table, position)
Pretty straightforward, it removes a defined 'drawer'. Position is the index or key value of the 'drawer'.

Example:

	pie = {"cherrypie", "applepie", "blueberrypie"} 	-- Creating the table.
		table.remove(pie, 1)				-- Removes the drawer with 1 as index, which is cherrypie.
		Cherrypie won't exist in the table pie anymore.

For k,v in pairs(table) do
This will go through all the elements of the table till the table's end and perform, if defined, an action on it. For instance I could print out every element as in key-value. This means that they'll show up as KEY VALUE. This is guaranteed to work with either a dictionary or a table. i,k (index-key) will also work if you're using a normal table.

Example:

pie = {"cherrypie", "applepie", "blueberrypie"} 	-- Creating the table.
		for k,v in pairs(pie) do				-- Tells the engine to go through all of the table and put the keys and values of the table in pairs and then do something with them.
		print(pie)					-- prints out the table as in KEY	VALUES.
		end						-- Ends the expression 'for'.
	Output:
		1	cherrypie
		2	applepie
		3	blueberrypie

Why would you want to use tables?
Simple. It can save time (both writing the script and running the script) and can avoid unneccesary loading. It also allows loading from external files and it can help if you want to add some easy user customisation.

Tables and a simple (or not so simple?) announcer
Now that we've had a basic introduction to tables, let's see what this can do for us in WoW.

announce1 = "Let's rock this thing!"		-- asigns the string "Let's rock this thing!"	 to the variable announce1.
announce2 = "I haven't used tables before."		-- asigns the string "I haven't used tables before." to the variable announce2.
announce3 = "What the heck?"				-- asigns the string "What the heck?" to the variable announce3.
announce = {announce1, announce2, announce3}		-- puts the variables announce1, announce2 and announce3 in the table. (If you will use " " here you'll store announce1 exactly, not the variable containing the information!

function Announcer_onSpawn(pUnit, Event)
pUnit:RegisterEvent("RandomAnnounce", 60000, 0)	-- Registers the event RandomAnnounce for pUnit to do every 60000 miliseconds (= 60 seconds).
end

function RandomAnnounce(pUnit, Event)
pUnit:SendChatMessage(14, 0, announce[math.random(1,3)])	-- This is where the magic happens. I'll explain this under here.
end

RegisterUnitEvent(ENTRYID, 18, "Announcer_onSpawn")

A closer look at this line.

pUnit:SendChatMessage(14, 0, announce[math.random(1,3)])

It sends out a chat message for pUnit but now we've replaced the string we are used to do with our announce table. It cannot yell out our table because we need to select which drawer it should use. As explained before table[index/key] will show the value for that index/key. Instead of a static number we have replaced it with a randomisation, which will draw a random number between 1 and 3 (including 1 and 3 of course).
So what if math.random(1,3) rolls 3? This means that the element/value with the index 3 will be called, which in this case is "What the heck?". Thus pUnit will now yell out "What the heck?".

Another example of tables in WoW
Another possibility of tables: spawning. This is not the whole script just the spawning part.

CreatureID = {57000, 57001, 57003, 57004, 57005}	-- These are entry ids of the mobs we want to spawn.
coordslocation = {500, -500, 10, 3} 				-- !Made up coordinates!. These are X, Y, Z, O.

function CreatureSpawning(pUnit, Event)
for k,v in pairs(CreatureID) do
pUnit:SpawnCreature(v, coordslocation[1]+math.random(-5,5), coordslocation[2]+math.random(-5,5), coordslocation[3], coordslocation[4], FACTION, DURATION) -- if you're using GuaEngine you'll also have equip1, equip2 and equip3
end	-- end for closing the 'for' statement
end	-- end for closing the function

A closer look at this:

for k,v in pairs(CreatureID) do
pUnit:SpawnCreature(v, coordslocation[1]+math.random(-5,5), coordslocation[2]+math.random(-5,5), coordslocation[3], coordslocation[4], FACTION, DURATION)

First of all we're putting the table in pairs again. Then we proceed to spawn a creature with entryid v which is value. The values are the elements in the CreatureID table. Because we're using in pairs it'll go through all of the table and use all of the values. So actually this tells the Lua engine to run that line with each v(alue) from the table until it reaches the end of the table, which in our case is three times (= 3 mobs!).
It's not neccessary to put the coordinates in a table. But I'm showing it this time, because it allows easier customisation and loading from an external (text) file. Anyway, I'll explain it nonetheless.
Coordslocation[1] means it'll open up the drawer with index 1, which is 500. It fills in 500 as X, but what's that? It's our friend math.random(-5,5) which will randomise our location a bit. It will draw a number between -5 and 5 and ADD it to the X coordinate. Same goes for the Y coordinate (= coordslocation[2]). Our Z coordinate is coordslocation[3] (= 10). And our O coordinate is coordslocation[4] (= 3)
Now because it actually runs the line 3 times seperately it means it will also do math.random(-5,5) 3 times. This means that the location of the spawning will change for each of the mob.

Note: You don't have to use different entryids for each mob. You can enter 57000 as many times as you'd like to and then the script will run the spawning line with entryid 57000 until the end of the table.


Additional notes
Thank you for reading. I hope it's been of any help to you.
Pay Lua.org a visit. It's a great source of information and there's even more to tables than 'just' this.
Keep on practising and messing around and you will get better.

[stoneharry]

Easy on the eyes to read and explained well +Rep
You should give some examples of what tables can be used for in terms of WoW to interest people into wanting to try and do that for themselves.

[Dynashock]

Yeah, I might come up with another example besides the announcer later this night. Thanks for the rep and comment.

[Troys]

+rep gave me a good idea of what a table is and how i can use this

[AngelSandy]

Here is an Example:

local SpellTable =
{123,345,567,890}

function SpellChoice(pUnit,event)
      pUnit:FullCastSpellOnTarget(math.random([SpellTable]),pUnit:GetRandomPlayer(0))
end

This should be a valid function.
What it does, is that it chooses a random spell in the Table I defined and casts it on a random Player in range.

(If it's not entirely correct please tell me ^^)

[Dynashock]

Here is an Example:

local SpellTable =
{123,345,567,890}

function SpellChoice(pUnit,event)
      pUnit:FullCastSpellOnTarget(math.random([SpellTable]),pUnit:GetRandomPlayer(0))
end

This should be a valid function.
What it does, is that it chooses a random spell in the Table I defined and casts it on a random Player in range.

(If it's not entirely correct please tell me ^^)

Not entirely correct.

It should be (the rest of your code is correct):

pUnit:FullCastSpellOnTarget(SpellTable[math.random(1,4)], pUnit:GetRandomPlayer(0))

What this tells Lua is: open drawer math.random(1,4) (so that's either 1, 2, 3 or 4) from the SpellTable table. So if it's 3, it'll open drawer 3 with as value 567.

You cannot use tables in math.random unless you define which values in the tables you want to use, like SpellTable[1]. Also you put SpellTable between [] and that tells Lua to open a table with SpellTable as key. But you haven't defined which table you want to open so it just doesn't work.

[AngelSandy]

Ah yes.

I couldn't remember if it was that way or, the other way around ^^
FIXED EXAMPLE

local SpellTable =
{123,345,567,890}

function SpellChoice(pUnit,event)
      pUnit:FullCastSpellOnTarget(SpellTable[math.random(1,4)], pUnit:GetRandomPlayer(0))
end

[Sounddead]

This is actually really good. +repx2

[Heliumz]

Oua ! love it! very useful! Thxss +Rep

[svedin]

Thanks, didn't know this. so Thanks

+Rep x2

[Mildan]

Awesome guide! Will surely come in handy! +rep