proc sort data=sashelp.zipcode out=ByZIP;
  where StateName="Delaware" and CountyNm="New Castle";
  by ZIP;
run;
data grouped;
  set ByZIP;
  if City ne lag(City)
  then Group+1;
run;
proc print data=grouped(obs=30);
  by Group City;
  id Group City;
  var ZIP Alias_City;
  title1 "ZIP Codes Grouped by City";
run;