Here you go:
data have;
infile datalines delimiter = ' ';
input week id year event_date;
datalines;
1 1 2015 1
1 1 2016 1
1 1 2021 2
2 1 2015 1
2 1 2016 1
2 1 2021 2
3 1 2015 1
3 1 2016 1
3 1 2021 2
1 2 2015 1
1 2 2016 1
1 2 2017 1
2 2 2015 1
2 2 2016 1
2 2 2017 1
3 2 2015 1
3 2 2016 1
3 2 2017 1
;
run;
proc sort data = have;
by week id year;
run;
data want;
set have;
by week id;
if last.id then output;
run;
Hopefully didn't miss something - let me know if I did.
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