如何得到每个个体在不同时间点的均值

1. data aaa;
   
2. input no time x;
   
3. cards;
   
4. 1 8 1
   
5. 1 8 2
   
6. 1 9 1
   
7. 1 9 2
   
8. 1 9 3
   
9. 1 10 2
   
10. 2 8 4
    
11. 2 9 5
    
12. 2 9 6
    
13. 2 9 7
    
14. ;
    
15. run;
    
16. 
    
17. /* 希望得到的数据 */
    
18. 1 8 1.5
    
19. 1 9 2
    
20. 1 10 2
    
21. 2 8 4
    
22. 2 9 6

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如何得到每个个体（id）在不同时间点（time）x的均值？谢谢！

proc sql;
select no,time,avg(x) as avg from aaa  group by no,time;
quit;

proc sql noprint;
create table want as
select no,time,mean(x) as mean from have group by no,time order by no,time;
quit;

proc sql noprint;
create table want as
select no,time,mean(x) as mean from have group by no,time order by no,time;
quit;

都是用SQL的 提供一个data步的思路

1. data aaa1;
   
2.         set aaa;
   
3.         by no time;
   
4.         retain x_ n_;
   
5.         if first.time then do; x_=0; n_=0; end;
   
6.         x_=x+x_;
   
7.         n_+1;
   
8.         y=x_/n_;
   
9.         if last.time;
   
10.         keep no time y;
    
11. run;

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data bbb(keep=no time mean);
set aaa;
by no time;
if first.no and first.time then do; num=0; total=0; end; /*防止上一号最大time与下一号最小time相同*/
if first.time then do; num=0; total=0; end;
total+x;
num+1;
if  last.time then do;
mean=total/num; output;
end;
run;

datastep ，proc sql，proc means ，proc summary，proc iml太多了。。。。。。。。。。