Lua - Tables Length

Size of the Table is the number of elements that are present inside the table. In case of numerically sized table, we've Lua operator # to get the table size correctly.

Lua does provide us a function to get the size of numerically sized array −

• #− used to get the size of numerically sized array.

Syntax

-- get the length of array using # operator
n = # (t)

• t− array

• n− size of the array

Example - Size of Numerically Indexed Table

# operator returns the size of the numerically indexed table. A table size will be one less than first integer index with nil value. In case of non-numeric keys, behaviour of # operator is not certain. Consider the following code:

main.lua

-- initialize a table
table = { 1, 2, 3}

-- print the length of the table as 3
print(#table)

-- add a non-numeric key to the table
table["a"] = 4

-- print the length of the table as 3
print(#table)

-- set one entry as nil
table[2] = nil

-- print the length of the table as 0
print(#table)

Output

When you build and execute the above program, it produces the following result −

3
3
3

Example - Computing Correct Size using counting method.

We can count each element using a for loop in the table, and then get the size of it.

main.lua

-- initialize a table
table = { 1, 2, 3}
table["a"] = 4

local count = 0
for _ in pairs(table) do 
   count = count + 1 
end
print(count)

Output

When you build and execute the above program, it produces the following result −

4

Example - Computing length of Table

Now let's encapsulate our counting logic within a function as len() and cover all the scenarios as discussed above in first example.

main.lua

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

-- initialize a table
table = { 1, 2, 3}

-- print the length of the table as 3
print(len(table))

-- add a non-numeric key to the table
table["a"] = 4

-- print the length of the table as 4
print(len(table))

-- set one entry as nil
table[2] = nil

-- print the length of the table as 2
print(len(table))

Output

When you build and execute the above program, it produces the following result −

3
4
3