Sort Part of a List

The reason why is that it is keeping Column B sorted. Column A is not alphabetical for the overall list, it is only alphabetical for each set of like-data in column B. Two-Column sort first sorts the first column, then sorts any grouped values in the second column.

ab - bb
ae - bb
ag - bb
aa - bc
ac - bd
ad -
af -

I need to imitate the possibility of
A. Sort column B (so empty space is on the bottom)
B. Sort column A where there is data in column B (B will become unsorted, but that is okay)

But even when doing that, Column A becomes fully re-sorted instead of just the selected data.