df_get_col_integer Function

    function df_get_col_integer(df, index) result(col)
        type(data_frame), intent(in) :: df
        integer, intent(in) :: index
        integer(ik), dimension(:), allocatable :: col

        type(column) :: data_col

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

        data_col = df % get_data_col(index)
        if (data_col % get_type() /= INTEGER_NUM) error stop "column is not integer type"

        col = data_col % geti()
    end function df_get_col_integer