do  -- Shannon entropy - translated from the Lua sample

    local function log2 ( x : number ) : number return math.log(x) / math.log(2) end

    local function entropy ( X : string ) : number
        local N, count, sum, i = X:len(), {}, 0
        for char = 1, N do
            i = X[char]
            if count[i] then
                count[i] += 1
            else
                count[i] = 1
            end
        end
        for n_i, count_i in pairs(count) do
            sum += count_i / N * log2(count_i / N)
        end
        return -sum
    end

    print( entropy( "1223334444" ) )
end