用first判断是否是新数据，再加一个自增数值

data aaa;
input x$;
cards;
a
b
a
c
b
c
c
.
;
run;
data aaa;
set aaa;
id=_n_;
run;
proc sort data=aaa out=aaasort;
by x;
run;
data aaasort;
set aaasort;
by x;
if missing(x) then y=.;
else if not missing(x) then  if first.x=1 then y+1;
output;
run;
proc sort data=aaasort out=aaa;
by id;
run;
data aaa;
set aaa;
drop id;
run;

data aaa;
input x$;
cards;
a
b
a
c
b
c
c
.
;
run;

data dataset1;
      set aaa;
          if x ne '' then rank='1';
          else rank='2';  
run;


proc sql;
      create table dataset2 as
          select distinct *
          from dataset1
      order by rank;
quit;


data dataset3;
      set dataset2;
      y=_n_;
          if x='' then y=.;
          drop rank;
run;
          
data dataset4;
      set aaa;
      rank=_n_;
run;

proc sql;
      create table dataset5 as
          select a.x,b.y
          from dataset4 as a left join dataset3 as b
          on a.x=b.x
      order by rank;
quit;