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Signature Description Parameters 
template<typename T>
std::pair<size_type, size_type>
fl_valid_index(const char *col_name) const;
This returns a pair containing the first and last indices of non-NaN/valid values in the requested column. If the column is empty or contains all NaN values, both indices will be zero.
 T: Type of the named column
col_name: Name of the column. It can be a data column name or DF_INDEX_COL_NAME
 
static void test_fl_valid_index()  {

    std::cout << "\nTesting fl_valid_index( ) ..." << std::endl;

    const double                nval = std::numeric_limits<double>::quiet_NaN();
    MyDataFrame                 df;
    std::vector<unsigned long>  idxvec = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 };
    std::vector<double>         dblvec = { 0, 15, -14, 2, 1, 12, 11, 8, 7, 6, 5, 4, 3, 9, 10};
    std::vector<double>         dblvec2 = { 100, 101, nval, 103, 104, 103.9, 106.55, 106.34, 1.8, nval, 112, 111.5, 114, nval, nval};
    std::vector<double>         dblempty { };
    std::vector<double>         allnan = { nval, nval, nval, nval, nval, nval, nval, nval, nval, nval, nval, nval, nval, nval, nval};
    std::vector<std::string>    strvec = { "", "bb", "cc", "ww", "", "ff", "gg", "hh", "ii", "jj", "kk", "ll", "mm", "nn", "" };

    df.load_data(std::move(idxvec),
                 std::make_pair("dbl_col", dblvec),
                 std::make_pair("dbl_col_2", dblvec2),
                 std::make_pair("Empty Col", dblempty),
                 std::make_pair("All NaN Col", allnan),
                 std::make_pair("str_col", strvec));

    const auto  res1 = df.fl_valid_index<double>("dbl_col");

    assert(res1.first == 0);
    assert(res1.second == 14);

    const auto  res2 = df.fl_valid_index<double>("dbl_col_2");

    assert(res2.first == 0);
    assert(res2.second == 12);

    const auto  res3 = df.fl_valid_index<double>("Empty Col");

    assert(res3.first == 0);
    assert(res3.second == 0);

    const auto  res4 = df.fl_valid_index<double>("All NaN Col");

    assert(res4.first == 0);
    assert(res4.second == 0);

    const auto  res5 = df.fl_valid_index<std::string>("str_col");

    assert(res5.first == 1);
    assert(res5.second == 13);
}

C++ DataFrame