Arrays

An array (or list) in Lua is a table with keys 1, 2, 3, ....

local fruits = {"apple", "banana", "cherry"}

print(fruits[1])
print(fruits[#fruits])
print(#fruits)
print(fruits[0])

fruits[#fruits + 1] = "date"
fruits[2] = "blueberry"
for i = 1, #fruits do
  print(i, fruits[i])
end

apple
cherry
3
nil
1	apple
2	blueberry
3	cherry
4	date

• Indexes start at 1 — fruits[0] is nil.
• #fruits is the length; fruits[#fruits + 1] = x appends.
• Loop with a numeric for from 1 to #t, or with ipairs (next lessons).

Holes break

# is only reliable for arrays without gaps (nil values in the middle):

local t = {1, 2, 3}
t[5] = 5
print(#t == 3 or #t == 5)

local u = {1, 2, 3}
u[2] = nil
print(u[1], u[2], u[3])

true
1	nil	3

With holes, # may return any "border", so the result isn't defined. To remove an element from the middle, use table.remove, which shifts the rest down.

Arrays of tables

local people = {
  {name = "Ada", age = 36},
  {name = "Linus", age = 28},
  {name = "Grace", age = 45},
}

local total = 0
for i = 1, #people do
  total = total + people[i].age
end
print(string.format("Average age: %.1f", total / #people))
print(people[2].name)

Average age: 36.3
Linus

A trailing comma after the last element is allowed and makes adding lines easier.

Practice

Create an array of five numbers and print the largest and the total.

local numbers = {12, 7, 31, 5, 18}
local largest, total = numbers[1], 0
for i = 1, #numbers do
  largest = math.max(largest, numbers[i])
  total = total + numbers[i]
end
print(largest, total)

31	73