In Lua, tables are versatile data structures that can be used as dictionaries, also known as associative arrays or hash tables. This powerful feature allows developers to store and retrieve data using key-value pairs efficiently.

Creating a Table as a Dictionary

To create a table that functions as a dictionary, simply use curly braces and assign key-value pairs:


local person = {
    name = "John Doe",
    age = 30,
    occupation = "Developer"
}

In this example, we've created a table called person with three key-value pairs.

Accessing and Modifying Values

You can access values using either dot notation or square bracket notation:


print(person.name)  -- Output: John Doe
print(person["age"])  -- Output: 30

-- Modifying values
person.occupation = "Designer"
person["age"] = 31

Dot notation is typically used for keys that are valid identifiers, while square bracket notation is more flexible and can handle any type of key.

Adding and Removing Key-Value Pairs

Adding new key-value pairs is straightforward:


person.email = "john@example.com"
person["phone"] = "555-1234"

To remove a key-value pair, simply assign nil to the key:


person.phone = nil

Iterating Over Dictionary Entries

Use the pairs() function to iterate over all key-value pairs in a table:


for key, value in pairs(person) do
    print(key .. ": " .. tostring(value))
end

Important Considerations

Lua tables are not ordered by default. If you need ordered key-value pairs, consider using an additional array to maintain the order.
Keys in Lua tables can be of any type except nil.
When using tables as dictionaries, be mindful of memory usage, especially with large datasets.

Common Operations

Checking if a Key Exists


if person.email then
    print("Email exists:", person.email)
else
    print("Email not found")
end

Getting the Number of Key-Value Pairs

Use the # operator with caution, as it only works reliably for sequence-like tables. For dictionaries, consider using a custom function:


local function tableLength(t)
    local count = 0
    for _ in pairs(t) do count = count + 1 end
    return count
end

print("Number of entries:", tableLength(person))

Related Concepts

To further enhance your understanding of Lua tables and their usage, explore these related topics:

By mastering tables as dictionaries, you'll unlock powerful data management capabilities in Lua, enabling you to create more efficient and flexible programs.