eq_real Function

    function eq_real(df, col, value) result(mask)
        type(data_frame), intent(in) :: df
        class(*), intent(in) :: col
        real(rk), intent(in) :: value
        type(boolean_mask) :: mask

        real(rk), dimension(:), allocatable :: col_data
        logical, dimension(:), allocatable :: result_mask
        integer :: col_index, i

        col_index = get_column_index(df, col)
        if (df % dtype(col_index) /= REAL_NUM) error stop "column is not real type"

        col_data = df_get_col_real(df, col_index)
        allocate (result_mask(size(col_data)))

        do i = 1, size(col_data)
            result_mask(i) = abs(col_data(i) - value) < 1.0e-10_rk
        end do

        call mask % new(result_mask)
        deallocate (col_data, result_mask)
    end function eq_real