"explain it like im 5" tables

hi, whiile i found i could grasp most of the basic concepts of programming in lua through trial and error, i am perplexed by tables, for some reason i just cannot get them, and i have read through many posts about them, but still no luck. the most i can do is to utilize arguments when i run a program, so i was hoping someone could take me through creating a table, adding to the table, getting values from a table, and also getting data out of a table containing unknown data (such as from a peripheral). im sorry if i am asking a lot, but ive realized the only way i will be able to really use them if i understand what each step is doing and why, thanks!

Tables are something that can hold lots of different strings and numbers. Make a table like this:

table = {}

You have now made a table called 'table'! Change this to:

table = {"foo","bar"}

The table now has the string "foo" and the string "bar" inside it. You can access these strings with variables. For example:

print(table[1])

This will print the first string in the table called 'table' on the screen. Similarly, this:

print(table[2])

will print the second one. You can also store numbers and booleans in tables. For example:

table = {3,"foo",true,"bar",7,false}

will store all of these in one table as table[1], table[2], table[3] etc.

This is useful for having one variable with everything instead of tons of unnecessary ones. If you do this:

for i = 1, #table do
  print(table[i])
end

it will print every single thing in the table called 'table'.

You can also store these to names, rather than numbers, like this:

table = {"foo" = "bar","hello" = "world"}

This means that, while our for loop to print everything won't work anymore as it uses numbers, we can do this:

print(table[foo])

and it will print "bar" or

print(table[hello])

and it will print "world".

Tables can also hold functions, and even become function, but that's a lot more complicated, so I won't go over that for now. Check the CC wiki and the Lua 5.1 documentation for more.

Shnupbups100, on 21 March 2014 - 11:12 PM said:

-snip

Do note that you should never call a table 'table', because 'table' is a reserved keyword in Lua. In fact, never use any reserved keywords as an identifier (variable name).

If you haven't seen this tutorial you should check it out; it's a good place to begin - wish I had found it when I was starting with tables. Hope that helps :)/>

Shnupbups100, on 21 March 2014 - 11:12 PM said:

You can also store these to names, rather than numbers, like this:

table = {"foo" = "bar","hello" = "world"}

This means that, while our for loop to print everything won't work anymore as it uses numbers, we can do this:

print(table[foo])

and it will print "bar" or

print(table[hello])

and it will print "world".

Tables can also hold functions, and even become function, but that's a lot more complicated, so I won't go over that for now. Check the CC wiki and the Lua 5.1 documentation for more.

Those last two aren't quite right. You can either do:

local v = tab.key

or

local v = tab["key"]

Doing what you did would get the value of the globals foo and hello (which is nil) and throw back a nil index error.

Also for tables if you wanted to take multiple variables and wanted to line them up like doing usernames and passwords you can do this. This basically checks if user1 which is username1 matches to anything in the table of username. (Which is does)

username = {"username1", "username2", "username3"}
user1 = "username1"
	for i, v in pairs(username) do
		if user1 == v then
		   print("User exists!")
		else
				   print("No")
		end
	end

The loop isn't needed if you instead use the keyes for your values. This makes it a lot more efficent when working with large tables.

username = {username1 = true, username2 = true, username3 = true}
user1 = "username1"
if username[user1] then
		   print("User exists!")
		else
				   print("No")
		end

CometWolf, on 23 March 2014 - 03:51 PM said:

The loop isn't needed if you instead use the keyes for your values. This makes it a lot more efficent when working with large tables.

username = {username1 = true, username2 = true, username3 = true}
user1 = "username1"
if username[user1] then
		   print("User exists!")
		else
				   print("No")
		end

True ,but it is a lot more effective for for loops because you can use it for other things such as using each username and putting a different value to it like a password instead of doing another if statement.

Which again would be less efficent. Just store the password in the username key. All you need is still one if statment.

if password == username[user1] then

wow, thanks guys, and sorry for getting back late, some stuff came up again . interesting, that clears it up a bit, but im still a bit confused on them, so could i perhaps throw up some snippets of code and have you tell me if im doing it right?

Go for it! Don't forget to use CODE tags :)/>

after doing some tests, i have a basic understanding of tables that i create, and how to use them. i am still having problems with tables that i dont create, such as from a peripheral, how would i get the data out of those?

(for some background, i am trying to pull info out of a table that i got from a openp scanner, the player data table in particular) everything i try just leads me to either it printing "1", "1table:*number*" just the table and number or "attempt to concate string and table, i assume this means that the table i got from the scanner contains other tables, and if so i am even more confused than before, help?

wait! i managed to figure it out by complete chance, for some reason printing the key and the value separately prints it correctly, thank you guys! one step closer to the augmented reality program i am working on!

edit: im not sure how to delete a post, so sorry for posting multiple replies, i have more questions, turns out there was a table in that table (dawg), how would i access that table? and also, is there a way to print a large table to that it doesnt go off screen? (i may be able to do this myself, im working on it as i post these)

Let's say you did something like this:

for key,value in pairs(playerTable) do
	print(key.." is of the type "..type(value))
end

Say one of the keys in the table, "hunter239833" for eg, was identified as another table.

To list what's in that, you could then pull:

for key,value in pairs(playerTable["hunter239833"]) do
	print(key.." is of the type "..type(value))
end

that worked, but another sort of problem… another table! i expect i do exactly the same thing? (tableception, am i right?)

ok, it worked, im going to quit posting on this topic now