proc sort data=sashelp.cars out=cars; 

  by Make DriveTrain Cylinders;

run;

​

data cars;

  set cars;

  by Make DriveTrain Cylinders;

​

  if first.Cylinders then grp_id + 1;

​

  * this answer gives you bonus information ! ;

  if first.Cylinders 

    then seq_in_group = 1; 

    else seq_in_group + 1;

run;