OK.
Let me try to solve it.

That is:
*** sort data ***;
proc sort data=trial out=trial_1;
    by var4;
run;

*** set by sorted var ***;
data trial_2;
    set trial_1;
    by var4;
    if not first.var4;
run;

"Delete" seems to be some kind of hard-coding, so I recommend to use method shown above.

Hope it helped you~

Best regards~

Thank you very much for your help. I'd like to know what does 'hard-coding' mean? And what's the difference between “if not first.var4” and “if first.var4 then delete”? Thank you.

OK.
Let me try to make myself clear.
What I mean is you can choose some obs from a certain set, but you'd better not to use dellete,update ect. It seems to be you change the original data by your will.
And hard-coding means you do sth without enough support by logical or statistical provement.
eg, if a=1 then b=3;
but you can't supply the logical relationship between them, then that's kind of hard-coding.
But all that above is my own opinion.
May it helps you~

Thank you indeed for your excellent explanation.

表酱索嘛~~~~人家要不好意思的拉~~~~偶是一只菜菜鸟~~~~

原来如此

先排序啊。。。。

多谢！

学习了！

by 语句后的变量加上notsorted 就可以不用排序了么   学习到了