[R] Assigning rank based on total count

[ws]

Hi all,

I am using ACS micro data (PUMS) with one of the columns as a 
factor for the place of birth (POBPF).  I would like to create 
a column (POBR) containing a rank 
corresponding to the place of the observation 
in the POBPF rankings.  For example, 
if a person is from Oregon, Oregon is 
the most popular Place of Birth, so each 
person who came from Oregon should have a 1 
in their POBR.  Each row from 
California would have POBR 2, etc.  

This way I can subset on the most populous sending 
places when doing analyses.

For the life of me I can't figure this out.  
I think some combination of "sort()", 
"xtabs()" and "merge()" should work, 
but my brain seems to be fried.

Tx