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

template<typename T, typename I = unsigned long>
struct SEMVisitor;

// -------------------------------------

template<typename T, typename I = unsigned long>
using sem_v = SEMVisitor<T, I>;
        
This functor class calculates the Standard Error of the Mean for a given column.
    explicit
    SEMVisitor (bool bias = true);
        
T: Column data type.
I: Index type.
static void test_SEMVisitor()  {

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

    std::vector<unsigned long>  idx =
        { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
          21, 22, 23, 24, 25, 26, 27, 28, 29, 31, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40 };
    std::vector<double> d1 =
        { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
          21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40 };
    MyDataFrame         df;

    df.load_data(std::move(idx), std::make_pair("col_1", d1));

    SEMVisitor<double>  sem_visitor;
    const auto          result = df.visit<double>("col_1", sem_visitor).get_result();

    assert(fabs(result - 1.84842) < 0.00001);
}