Signature Description Parameters
#include <DataFrame/DataFrameStatsVisitors.h>

template<typename T,
         typename I = unsigned long,
         typename =
             typename std::enable_if<std::is_arithmetic<T>::value, T>::type>
struct EntropyVisitor;
        
This visitor calculates the rolling values of information entropy
In information theory, the entropy of a random variable is the average level of "information", "surprise", or "uncertainty" inherent in the variable's possible outcomes. The concept of information entropy was introduced by Claude Shannon in his 1948 paper.
A die has higher entropy (p=1/6) versus a coin (p=1/2).
    explicit
    EntropyVisitor(size_type roll_count, value_type log_base = 2);
        
T: Column data type.
I: Index type.
static void test_EntropyVisitor()  {

    std::cout << "\nTesting EntropyVisitor{  } ..." << std::endl;

    std::vector<unsigned long>  idx =
        { 123450, 123451, 123452, 123453, 123454, 123455, 123456, 123457, 123458, 123459, 123460, 123461, 123462, 123466, 123467, 123468,
          123469, 123470, 123471, 123472, 123473, 22, 23, 24, 25, 26, 27, 28
        };
    std::vector<double>         close =
        { 1.80, 2.80, 1.90, 14.00, 1.10, 6.00, 13.00, 8.00, 9.00, 2.80, 1.90, 4.30, 20.00, 1.85, 3.00, 34.00, 67.00, 23.00, 87.00, 9.00, 45.00,
          1.00, 11.00, 456.00, 34.00, 7.00, 7778.00, 5.00
        };
    MyDataFrame                 df;

    df.load_data(std::move(idx), std::make_pair("close", close));

    EntropyVisitor<double>  e_v (5);

    df.single_act_visit<double>("close", e_v);

    assert(e_v.get_result().size() == 28);
    assert(std::isnan(e_v.get_result()[0]));
    assert(std::isnan(e_v.get_result()[7]));
    assert(std::abs(e_v.get_result()[8] - 2.18974) < 0.00001);
    assert(std::abs(e_v.get_result()[10] - 1.98477) < 0.00001);
    assert(std::abs(e_v.get_result()[14] - 1.7154) < 0.0001);
    assert(std::abs(e_v.get_result()[27] - 0.596666) < 0.00001);
    assert(std::abs(e_v.get_result()[25] - 0.822228) < 0.00001);
    assert(std::abs(e_v.get_result()[22] - 1.49397) < 0.0001);
}