Tables: Lua's Only Data Structure

Lua has exactly one built-in data structure, the table, and it does the job of arrays, dictionaries/maps, and even objects in other languages.

Tables as arrays

Lua

local scores = {90, 85, 100}

print(scores[1])       -- 90, indices start at 1
print(#scores)          -- 3, the length operator

table.insert(scores, 75)  -- appends to the end
table.remove(scores, 1)   -- removes the first element, shifts the rest down

for i, score in ipairs(scores) do
  print(i, score)
 end

local scores = {90, 85, 100}

print(scores[1])       -- 90, indices start at 1
print(#scores)          -- 3, the length operator

table.insert(scores, 75)  -- appends to the end
table.remove(scores, 1)   -- removes the first element, shifts the rest down

for i, score in ipairs(scores) do
  print(i, score)
 end

ipairs iterates a table in order from index 1 until the first nil, exactly what you want for array-like tables.

Tables as maps/objects

Lua

local player = {
  name = "Ada",
  xp = 250,
  ["favorite color"] = "blue", -- keys with spaces need bracket syntax
}

print(player.name)               -- dot syntax, sugar for player["name"]
print(player["favorite color"])  -- bracket syntax, required for non-identifier keys

player.level = 3 -- adding a new key is just an assignment

for key, value in pairs(player) do
  print(key, value)
end

local player = {
  name = "Ada",
  xp = 250,
  ["favorite color"] = "blue", -- keys with spaces need bracket syntax
}

print(player.name)               -- dot syntax, sugar for player["name"]
print(player["favorite color"])  -- bracket syntax, required for non-identifier keys

player.level = 3 -- adding a new key is just an assignment

for key, value in pairs(player) do
  print(key, value)
end

pairs iterates every key in a table, in an unspecified order, use it for map-style tables where order doesn't matter. player.name and player["name"] always refer to the exact same table entry, dot syntax is purely a convenience for string keys that are valid identifiers.

TIP

Because arrays, maps, and objects are all "just a table" in Lua, a single table can even mix both styles: numeric indices for a list part and named keys for extra fields on the same object.

Tables: Lua's Only Data Structure

Tables as arrays

Tables as maps/objects

📝 Tables Quiz