table

A table is the most important data structure of Lua. They are used to construct arrays, objects and more. They are initalized with the {} constructor.

myTable = {}

Technically, tables are associative arrays with an automatic numeric key that starts at 1, so tables are used for arrays as well as objects.

Ordered tables

An example of an ordered table array:

fruits = {'apple', 'banana', 'tangerine', 'fig'}

Lua is 1-indexed. To get the first item from the array:

print(fruits[1]) --"apple"

Length of an ordered table

Tables have the special # keyword. Prepending this to the table name returns the table's length.

fruits = {'apple', 'banana', 'tangerine', 'fig'}
print("I have "..#fruits.." fruits.") --"I have 4 fruits."
print("The last one is "..fruits[#fruits]) --"The last one is fig."

You can easily add an item to the end of an ordered table using the length of the table and adding 1. This added item becomes the new end of the table.

fruits[#fruits + 1] = 'lemon'
print(fruits[#fruits]) --"lemon"

Looping through an ordered table

There is the special function ipairs to loop through an ordered table. The i references index, the number that counts forward through the table.

for i,fruit in ipairs(fruits) do
  print(fruit)
end
--prints out:
apple
banana
tangerine
fig

Associative tables

Tables can be used to build objects made up of more complex key-value pair structures.

me = {
  ['name'] = 'Mario',
  ['job'] = 'Plumber'
}

You can access values from the table in two different ways, through the [key] construct or dot notation:

print(me['name']) --'Mario'

print(me.name) --'Mario'

You can loop through key-value pairs in a table through the special pairs function.

for key,val in pairs(me) do
  print(key,val)
end
--prints
job Plumber
name    Mario

Table manipulation

Lua has a number of functions specific to working with tables. See the Table Manipulation in the Lua Reference Manual for more information.

table.concat(list [,separator]) --concatenates all items in the table, optionally with a separator
table.insert (list, [pos,] value) --inserts item to end of table, or at optionally specified location 
table.move(a1, f, e, t, [a2]) --moves items from a table within or to another
table.pack(...) --returns a table with all arguments
table.remove(list [,pos]) --removes an element from the end of table, or at optionally specified location
table.sort(list [,comp]) --sorts a list by alphanumeric or an optionally given order
table.unpack(list) --returns elements from a list

Advanced use of tables

Tables are used for other data constructors. You can create an array of objects; build object-oriented programming classes; and mimic inheritance, all with metatables.

Syntax

myTable = {}

myTable = {n1, n2, n3, .....}

myTable = {
  [key] = value,
  [key] = value,
  .....
}

etc.

Related

• function()
• for