df_get_val_character Function

    function df_get_val_character(df, row_index, col_index) result(val)
        type(data_frame), intent(in) :: df
        integer, intent(in) :: row_index, col_index
        character(len=:), allocatable :: val

        type(column) :: data_col

        if (col_index < 1 .or. col_index > df % ncols()) error stop "column index out of range"

        data_col = df % get_data_col(col_index)
        if (data_col % get_type() /= CHARACTER_NUM) error stop "column is not character type"

        val = data_col % getch(row_index)
    end function df_get_val_character