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st: drop conditioning on 2 different variables


From   "Ann Miller" <MILLERA@hsph.harvard.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: drop conditioning on 2 different variables
Date   Fri, 01 May 2009 16:34:08 -0400

Dear Statalist, 

I am trying to clean some data, in which I have 2 different and contradictory lab results on the same date. Example:

id             cd4c	cd4cdate
1	325	01 Mar 06
1	352	01 Mar 06
1              500          03 Aug 06
2	167	20 Mar 06
2	302	20 Mar 06
2              900          12 Dec 06
3	118	20 Oct 05
3	178	20 Oct 05
3              450          01 May 06

I want to drop the row with the highest cd4c date when there's a date match. This is proving to be surprisingly hard to do. I tried
sort id cd4c cd4cdate
bysort imbd_id cd4cdate: gen min= cd4c[1]
and then tried to replace the cd4c with min, but in this case, min was not always the smallest cd4. I suspect that's because when I sort based on the date, it doesn't also sort by the cd4c value. Is there a way that I can reliably drop the row with the largest CD4c value when id and cd4cdate match? 

Many thanks!

--Ann



Ann C. Miller, PhD, MPH
Research Associate
FXB Center for Health and Human Rights
Harvard School of Public Health
651 Huntington Ave, 7th Floor
Boston, MA 02115
(617) 432-7297

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