You can count occurrences of t > 0 separately by patient. 
egen tcount = sum(t > 0), by(patient)  
Then counting patients, not recordings, is possible e.g. by tagging, say
egen tag = tag(patient) 
count if tag & tcount 
For much more detail, see the thread started on 18 March by Daniel
McNeil. 
Bill Gould gave the first principles answer, while I gave an -egen-
answer. 
They are complementary. 
Nick 
Johannes Geyer
I have some results on 236 patients and each patient has 57 recordings 
stored in a single variable t. I am trying to count how many of these 
patients have a score of t>0. I tried the following code:
gen tcount=0
forvalues i=1/236{
    forvalues j=1/57{
    if patient==`i' & t>0 {
    then tcount==tcount+1 
    continue
}
I think a loop is unnecessary here  - you just want to count, right?
There 
are many solutions, e.g.
count if t >0 & t<.
(saved in r(N))
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