Counting Fields in a Lua Table

The Lua # operator is intended for sequence-like tables with consecutive integer keys. It is not a general count of every field, especially when the table contains holes or string keys.

To count all entries whose value is not nil, iterate with pairs:

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

For { "a", "b", "c" }, #t is appropriate. For { name = "Ada", score = 10 }, use an explicit loop such as table.nums(t).