data ccc;
        set bbb;
        by id x x1;
        if last.x then output;
run;

试试这个
data aa;
set bbb;
idx=compress(id," ")||compress(x," ");
run;
proc sql;
create table a as
select id,x,max(x1) as x1
from aa
  group by idx;
quit;
proc sort data=a nodupkey;
by id  x;
run;