嗯，谢谢！我最后是用的proc summary,输出N,然后merge了一下。

我在google group上找到了这样的解决方案(来源:https://groups.google.com/forum/#!topic/comp.soft-sys.sas/Pb-zj08QYBw):

The SQL solution,
proc sql;
  create table csLargeEnough as
  select * from tsdata
  group by csid having count(*)>= n
  ;
quit;
will limit the dataset csLargeEnough to groups of tuples (rows) in
each cross-section of at least n tuples.
少于n的横截面都会被删掉.希望能有帮助.