Tables

A table is a useful way to store multiple values in one value. It is called a table because it acts like a grid with two columns:

Key	Value

The key column is used to find a row in the table, and the value is the value that is stored in that row. Both the key and value can be any Lua value (numbers, strings, the values of variables, Parts etc., even other tables!) except nil.

Creating a table

To create a table we use a pair of curly brackets ({}). We can then store the table in a variable:

myTable = {}

Indexing a table

Getting values into and out of a table is called indexing. First we need the key for the row we want to get or change the value in. We write this in square brackets ([]) after the table is in. For example, to get or change the row with the key 1 in the table myTable, we would write myTable[1]. We can then use this exactly like a variable: we can use its value in other places, or we can set it. For example, to store the string "A value" in myTable in the row with the key 1, we would write:

myTable[1] = "A value"

Now we can use myTable[1] in other places:

print(myTable[1]) -- prints: A value

If there is already a row in the table with the key we're trying to set, the old one will be changed:

myTable[1] = "A new value"
print(myTable[1]) -- prints: A new value

If there isn't a row with the key we're using when we try to get a value, we will get nil:

print(myTable[2]) -- prints: nil

More on creating tables

We can add keys to the table while we are creating a table in a very similar way to indexing. Inside the curly brackets, we can put lines that are very similar to indexing, but without the name of the table, and separated by commas.

myOtherTable = {
    [1] = "A value",
    ["A string key"] = "Another value",
    [2] = 5
}
print(myOtherTable[1], myOtherTable["A string key"], myOtherTable[2]) -- prints: A value Another value 5

The commas are important! If they are not there, Lua will give an error message saying it expects the "}".

Arrays

An array, or list, is a table were all the keys are whole numbers (e.g. 1, 2, 3, 4...). This is very useful for creating lists of things, such as a list of people who can use a tool.

When we are creating arrays, we can miss out the ["key"] = part, and just write the values separated by commas, and Lua will automatically use the numbers 1, 2, 3, 4, 5... as the keys:

myArray = {"First value", "Second value", "Third value"}
print(myArray[1]) -- prints: First value
print(myArray[2]) -- prints: Second value
print(myArray[3]) -- prints: Third value

We can get the number of values in an array (but not a normal table, only number keys are counted) by using the # operator:

print(#myArray) -- prints: 3

Lua's table manipulation functions allow you to easily do things such as add and remove values from an array.

Note: Normally, nil should not be used as a value in an array. # and Lua's table manipulation functions use nil to tell where an array ends. Putting them in the middle of your table may make Lua think the array ends there.

Loops through tables

We can use the pairs and ipairs functions to write a loop that goes through every value in an array:

for key, value in pairs(myOtherTable) do
    print(key, "=", value)
end

Outputs:
1 = A value
A string key = Another value
2 = 5

for key, value in ipairs(myArray) do
    print(key, "=", value)
end

Outputs:
1 = First value
2 = Second value
3 = Third value

The difference between pairs and ipairs is that ipairs is designed for arrays - it only goes through the keys 1, 2, 3... until it finds a nil value. pairs goes through all the keys, but might not go through them in a set order.

Pass by reference

An important thing to understand when setting more than one variable to the same table is that tables are passed by reference. This means that the variable doesn't directly contain the table itself, but that it holds a reference to it. This means that when more than one variable is set to a table, the variables don't each have a copy of the table, they refer to the same table, so any changes will be noticed by both variables:

var1 = {}
var2 = var1
var2["key"] = "value"
print(var1["key"]) -- prints "value"!

See Also

Metatables

2.5 - Tables

3.6 - Table Constructors

11.2 - Matrices and Multi-Dimensional Arrays