Checking for Duplicate Ids | SAS Code Fragments

data ids;
  input id;
cards;
1
2
3
4
4
5
6
7
7
8
8
9
;
run;

proc sort data=ids out=ids2;
  by id;
run;

data dupes;
  set ids2;
  by id;
  if not (first.id and last.id) then output;
run;

proc print data=dupes;
run;