Dear friends,
  i have a dataset like this:
x y z
1 2 3
2 3 1
3 2 1
1 1 3
2 1 2
3 2 3
2 1 1
I want to replace x with the following values:1<-a,2<-b,3<-c,4<-d;
             replace y with the following values:1<-b,2<-a,3<-c,4<-d;
             replace z with the following values:1<-d,2<-c,3<-b,4<-a;
Finally,select two subsets:
1. if x='a';
2.x='a' and y='a';
 thanks very much!



-- 
Kind Regards,
Zhi Jie,Zhang ,PHD
Department of Epidemiology
School of Public Health
Fudan University
Tel:86-21-54237149

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