Dear All

First time poster. Using Stata 15.1 on Windows.

I am doing a epidemiologic register study on adverse events in colonoscopy. So for each colonoscopy I want to check if the same individual/same id came in with a bleeding or perforation the next 30 days. The data sett is very large with 32 million entries in two files.

This is the code I found that I was trying out, just to do a simple loop. What I want to do is just when colonoscopy == 1 then do a lot more only if colonoscopy == 1.

foreach var in colonoscopy {
if _rc==0 {
//Check if the same id has an Perforation the next 30 days.
//Only if colonoscopy == 1
}
}

But it it enters the loop even if colonoscopy is blank or 0.
How can i do this so it enters only if colonoscopy is equal to 1?

Here is sample of the dummy test dataset.

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input byte id float(colonoscopy Perforation)
1 . .
1 . .
1 . .
2 . .
2 . .
2 1 .
2 . .
2 . 1
2 . 1
2 . .
2 . .
2 . .
2 . .
2 . .
2 . .
2 . .
2 . .
1 . .
3 . .
3 . .
end


Thanks in advance
Bjarki