st: Code to generate variable indicating date that CD4 drops below 250

["Polis, Chelsea B." <cpolis@jhsph.edu>]

Dear Statalisters,

I would like to create a variable in my dataset to indicate the date at
which a subjects CD4 counts dropped below 250.  My data is currently in
wide format, and each subject had anywhere from 1 to 19 visits.  For each
subject, I have up to 19 variables that indicate cd4 count (i.e., cd41 cd42
cd43 cd44 and so on), and up to 19 variables that indicate visit  date
(visitdate1 visitdate2 visitdate3 visitdate4 etc.).  I'd like to create a
variable to indicate the first date at which CD4 count dropped below 250,
if it ever dropped below 250.

Any suggestions on how to write such a code?

Many thanks,
Chelsea

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