/*  C04S6D01 */

/*  PROC SORT with NODUPKEY option  */

proc sort data = ia.DupRoutes out = dupRoutes nodupkey;
  by RouteID RouteStart RouteDestination ScheduledArrivalTime
       ScheduledDepartureTime;
run;

/*  PROC SORT followed by DATA step with FIRST. processing  */

proc sort data = ia.DupRoutes out = DupRoutes;
   by RouteID RouteStart RouteDestination ScheduledArrivalTime
        ScheduledDepartureTime;
run;
data duproutes;
		set duproutes;
    by RouteID RouteStart RouteDestination ScheduledArrivalTime 
     ScheduledDepartureTime;
    if first.ScheduledDepartureTime;
run;