st: Creating drugs combination

[Michele Santacatterina <miksanta@hotmail.it>]

Dear StataList,

I have an issue. I am trying to create, from a HIV database, a variable containing the value of different drug combinations (name regimen) and the number of drugs (number of drugs)$

ID      treatstart      treatstop       drug            name_regimen    number_of_drugs
2       24-Aug-95       14-Nov-97       ZDV             ZDV+3TC                 2
2       24-Aug-95       13-Feb-03       3TC
2       7-Aug-96        14-Nov-97       LOV             ZDV+3TC+LOV             3
2       14-Nov-97       15-Jun-00       IDV             3TC+IDV+d4T             3
2       14-Nov-97       13-Feb-03       d4T
2       15-Jun-00       13-Feb-03       IDV             3TC+IDV+RTV             3
2       15-Jun-00       13-Feb-03       RTV

Patient 2 started ART at 24-Aug-95 with ZDV+3TC and at 7-Aug-96, LOV was added to the treatment becoming ZDV+3TC+LOV. At 14-nov-97 he finished with ZDV and LOV and he started with $

If I run the command 

by infcare_ID treatstart, sort: gen n_trt = _n

for the number of drugs, i obtain at 7-Aug-96 just one drug (LOV) and not 3 as I should have (ZDV+3TC+LOV).

Hoping I have been clear enough.
Someone knows how to do it?

Thank you in advance.

Michele



*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/