Filling null values

I have a table that looks like this:

homeid city date measurement pre/post
123 san francisco 1/2/2003 1458 pre
123 san francisco NULL 1932 post
124 los angeles 2/4/2005 938 pre
124 NULL NULL 266 pre
124 los angeles 7/4/2006 777 post

I'd like to write a query so that I get the following result:

homeid city date measurement pre/post
123 san francisco 1/2/2003 1458 pre
123 san francisco 1/2/2003 1932 post
124 los angeles 2/4/2005 938 pre
124 los angeles 2/4/2005 266 pre
124 los angeles 7/4/2006 777 post

If a city or date is null, then it will fill from other not null
values with the same homeid. If given the choice, it will
preferentially fill from a row where homeid AND pre/post match. But
if that doesn't match, then it will still fill from the same homeid.

Does anyone have ideas for this?

Thanks,
Jeff