SAS9.2 中first. last. 的使用求助

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我想将数据库（按变量var4排序）中每个var4取值的记录中的第一条删除，建立一个新的数据集，在运行以下程序后，SAS 日志中提示：
“NOTE: 变量 first.var4 未初始化。
   NOTE: 有 1331 个从数据集 WORK.TRIAL 读取的观测。
   NOTE: 数据集 WORK.TRIAL2 有 1331 个观测和 35 个变量。
   NOTE: “DATA 语句”所用时间（总处理时间）:
      实际时间          0.01 秒
      CPU 时间          0.01 秒”
请问这是什么原因，是程序编写有错误还是软件或其他问题？请高手指点。

程序如下：
data trial2;
set trial;
if first.var4 then delete;
run;

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关键词：First Last FIRS SAS9 FIR 程序编写 数据库 记录 软件

在用first和last变量之前要根据前面的var4排序的，你排序了吗？

要想用first.variable，首先要有by语句，并且by后面必须要包括这个variable，不过这个变量不一定非要排序，可以用 notsorted 选项。

如：

1. data have;
   
2.         input num value;
   
3. cards;
   
4. 1 2
   
5. 1 5
   
6. 2 2
   
7. 2 3
   
8. 3 4
   
9. 1 5
   
10. 1 3
    
11. ;
    
12. 
    
13. data want;
    
14.         set have;
    
15.         by num notsorted;
    
16.         if first.num then delete;
    
17. run;

复制代码

谢谢楼上老师的指点！

chaoren2010 发表于 2012-7-18 19:14
谢谢楼上老师的指点！

言重啊，我不是老师。。

看来楼主没有排序

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~

lynette_89 发表于 2012-7-19 22:02
OK.
Let me try to solve it.

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.

chaoren2010 发表于 2012-7-28 12:12
Thank you very much for your help. I'd like to know what does 'hard-coding' mean? And what's the d ...

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~

lynette_89 发表于 2012-7-28 15:30
OK.
Let me try to make myself clear.
What I mean is you can choose some obs from a certain set ...

Thank you indeed for your excellent explanation.