data x;
input Code        Year        ML        BL        LTU;
cards;
/*数据区*/
;run;

/*设每组code需要删除的year数目定义为n，若源数据每组year数目不足n的则定义为删除整组*/

%let n=3;
proc sql noprint;create table x_new as select *,count(*)/4 as d
from x group by code having d>&n ;
select * from x_new order by code , year desc;
create table final as select  * from x_new group by code
having min(year)+&n<=year<=max(year) order code ,year desc;quit;

proc sort data=x;
  by code descending year ;
run;

data final(drop count);
  set x;
  by code descending year;
  count+1;
  if first.code then count=1;
  if count>3;
run;

Here is one-step data step solution. It is assumed that data is sorted by code and year.

data a;
  do code=1,2,3;
     numyear=ceil(ranuni(567)*10)+3;
         do i=1 to numyear;
           year=2000+i;
           output;
         end;
end;
drop i numyear;
run;

data b;
n=0;
do until(last.code);
  set a;
  n+1;
  by code;
end;
l=0;
do until(last.code);
  set a;
  l+1;
  by code;
  if l<=n-3 then output;
end;
keep code year;
run;

proc print; run;

请问用二楼的方法怎么删除5年和10年的数据？
3年的删除很成功，不过把3改成5以后，后面几排数据就乱了。

说的太难了吧