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

template<typename T, typename I = unsigned long>
struct DotProdVisitor;
This functor class calculates the dot-product of two given columns. It also calculates the magnitude, Euclidean distance, and Manhattan distaice of two columns.

get_result(): Returns the dot product of both columns
get_magnitude1(): Returns the magnitude of the first column
get_magnitude2(): Returns the magnitude of the second column
get_euclidean_dist(): Returns the Euclidean distance of two columns
get_manhattan_dist(): Returns the Manhattan distance of two columns
 T: Column data type.
I: Index type. 
static void test_view_visitors()  {

    std::cout << "\nTesting View visitors ..." << std::endl;

    MyDataFrame df;

    StlVecType<unsigned long>  idxvec = { 1UL, 2UL, 3UL, 4UL, 5UL, 6UL, 7UL, 8UL, 9UL, 10UL };
    StlVecType<double>         dblvec1 = { 1.1, 2.2, 3.3, 4.4, 5.5 };
    StlVecType<double>         dblvec2 = { 2.2, 3.3, 4.4, 5.5, 6.6 };
    StlVecType<double>         dblvec3 = { 0.0, 1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7, 8.8, 9.9 };
    StlVecType<double>         dblvec4 = { 5.9, 4.4, 1.0, 9.8, 5.3, 7.2, 3.8, 4.1 };
    StlVecType<double>         dblvec5 = { 1.1, 5.9, 4.4, 1.0, 9.8, 5.3, 7.2, 3.8, 4.1, 10.1 };
    StlVecType<double>         dblvec6 = { 1.1, 1.1, 3.3, 3.3, 1.1 };

    df.load_data(std::move(idxvec),
                 std::make_pair("dbl_col1", dblvec1),
                 std::make_pair("dbl_col2", dblvec2),
                 std::make_pair("dbl_col3", dblvec3),
                 std::make_pair("dbl_col4", dblvec4),
                 std::make_pair("dbl_col5", dblvec5),
                 std::make_pair("dbl_col6", dblvec6));

    typedef StdDataFrame128<unsigned long>::View MyDataFrameView;

    MyDataFrameView dfv = df.get_view_by_idx<double>(Index2D<unsigned long> { 2, 4 });

    assert(dfv.get_index().size() == 3);

    MeanVisitor<double> mean_visitor;

    assert(fabs(dfv.visit<double>("dbl_col1", mean_visitor).get_result() - 3.3) < 0.00001);

    DotProdVisitor<double>  dp_visitor;

    dfv.visit<double, double>("dbl_col1", "dbl_col2", dp_visitor);
    assert(fabs(dp_visitor.get_result() - 45.98) < 0.00001);
    assert(fabs(dp_visitor.get_magnitude1() - 5.92368) < 0.00001);
    assert(fabs(dp_visitor.get_magnitude2() - 7.77817) < 0.00001);
    assert(fabs(dp_visitor.get_eculidean_dist() - 1.90526) < 0.00001);
    assert(fabs(dp_visitor.get_manhattan_dist() - 3.3) < 0.00001);

    dfv.single_act_visit<double, double>("dbl_col1", "dbl_col2", dp_visitor);
    assert(fabs(dp_visitor.get_result() - 45.98) < 0.00001);
    assert(fabs(dp_visitor.get_magnitude1() - 5.92368) < 0.00001);
    assert(fabs(dp_visitor.get_magnitude2() - 7.77817) < 0.00001);
    assert(fabs(dp_visitor.get_eculidean_dist() - 1.90526) < 0.00001);
    assert(fabs(dp_visitor.get_manhattan_dist() - 3.3) < 0.00001);
}

C++ DataFrame