Hi All,

Here's an example of the sort of dataset that I'm working with:

clear
input studyid edvisits frequent_user
1 0 1
1 2 1
1 1 1
1 0 1
1 0 1
2 0 0
2 0 0
2 0 0
2 0 0
2 0 0
3 1 1
3 0 1
3 2 1
3 0 1
3 0 1
4 1 0
4 0 0
4 0 0
4 0 0
4 1 0
end

I am trying to subset out the data to create 3 separate datasets: people with no ed visits, people with few ed visits, and people with frequent ed visits.

For example, the "few ed visits" dataset would contain all the records for the person with studyid #4 and the the "frequent ed visits" dataset would contain
all records for studyid # 1 and 3

By looking around the forums I think the code should look something like this:
*no edvisits*
bysort studyid (edvisits) : drop if edvisits[1] > 0

*few edvisits*
bysort studyid (edvisits) : drop if edvisits[1] == 0
bysort studyid (frequent_user) : drop if frequent_user == 1

*frequent edvisits*
bysort studyid (edvisits) : drop if edvisits[1] == 0
bysort studyid (frequent_user) : keep if frequent_user == 1

but I don't seem to be having any success so I'm clearly missing something.

think i've gotten close to the answer with these these two posts, but like I said, no luck so far. Any help would be much appreciated: https://www.stata.com/statalist/archive/2005-08/msg00361.html
https://www.statalist.org/forums/forum/general-stata-discussion/general/1396103-drop-whole-group-of-observations-if-one-fulfils-condition