Signature Description Parameters

template<typename ... Ts>
DataFrame<I>
get_data(const std::vector<const char *> col_names) const;
        
This returns a DataFrame with index and col_names copied from the original DataFrame Ts: List types of col_names
col_names: List of column names

template<typename ... Ts>
View
get_view(const std::vector<const char *> col_names);
        
It behaves like get_data(), but it returns a View. A view is a DataFrame that is a reference to the original DataFrame. So if you modify anything in the view the original DataFrame will also be modified.
NOTE: There are certain operations that you cannot do with a view. For example, you cannot add/delete columns, etc.
Ts: List types of col_names
col_names: List of column names

template<typename ... Ts>
ConstView
get_view(const std::vector<const char *> col_names) const;
        
Same as above view, but it returns a const view. You can not change data in const views. But if the data is changed in the original DataFrame or through another view, it is refelcted in the const view. Ts: List types of col_names
col_names: List of column names
static void test_get_data()  {

    std::cout << "\nTesting get_[data|view]() ..." << std::endl;

    StlVecType<unsigned long>  idx =
        { 123450, 123451, 123452, 123453, 123454, 123455, 123456, 123457, 123458, 123459, 123460, 123461, 123462, 123466 };
    StlVecType<double> d1 = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 };
    StlVecType<double> d2 = { 8, 9, 10, 11, 12, 13, 14, 20, 22, 23, 30, 31, 32, 1.89 };
    StlVecType<double> d3 = { 15, 16, 17, 18, 19, 20, 21, 0.34, 1.56, 0.34, 2.3, 0.1, 0.89, 0.45 };
    StlVecType<int>    i1 = { 22, 23, 24, 25, 99, 100, 101, 3, 2 };
    MyDataFrame        df;

    df.load_data(std::move(idx),
                 std::make_pair("col_1", d1),
                 std::make_pair("col_2", d2),
                 std::make_pair("col_3", d3),
                 std::make_pair("col_4", i1));

    auto    df2 = df.get_data<double, int>({ "col_1", "col_4"});

    assert((! df2.has_column("col_2")));
    assert((! df2.has_column("col_3")));
    assert((df2.get_column<double>("col_1")[11] == 12));
    assert((df2.get_column<int>("col_4")[8] == 2));
    assert((df2.get_index()[3] == 123453));

    typedef MyDataFrame::View MyDataFrameView;
    typedef MyDataFrame::ConstView MyDataFrameConstView;

    const MyDataFrame       &const_df = df;
    MyDataFrameView         df3 = df.get_view<double, int>({ "col_1", "col_4"});
    MyDataFrameConstView    const_df3 = const_df.get_view<double, int>({ "col_1", "col_4"});

    assert((! df3.has_column("col_2")));
    assert((! df3.has_column("col_3")));
    assert((df3.get_column<double>("col_1")[11] == 12));
    assert((df3.get_column<int>("col_4")[8] == 2));
    assert((df3.get_index()[3] == 123453));

    df3.get_index()[3] = 100;
    df3.get_column<int>("col_4")[8] = 101;
    df3.get_column<double>("col_1")[11] = 102.2;

    assert((df3.get_column<double>("col_1")[11] == 102.2));
    assert((df3.get_column<int>("col_4")[8] == 101));
    assert((df3.get_index()[3] == 100));
    assert((df.get_column<double>("col_1")[11] == 102.2));
    assert((df.get_column<int>("col_4")[8] == 101));
    assert((df.get_index()[3] == 100));

    assert((const_df3.get_column<double>("col_1")[11] == 102.2));
    assert((const_df3.get_column<int>("col_4")[8] == 101));
    assert((const_df3.get_index()[3] == 100));
}
C++ DataFrame