Whoops, of course you're right. When I play with things to work out code I usually don't keep the changes, so I mangle working datasets willy-nilly and didn't think to change the Conditioned keep to a conditioned list. The use of bysorting and _N is much neater and more flexible.

N.J.Cox wrote: >Whoa! The question was just about _listing_. >You just changed Raoul's dataset by throwing >much of it away.

* * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/