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How to append the random no.s for different variables in the same data.frame

Hi
Why do you want to write csv files? Maybe it would be better to form this data frame directly.
As you did not provide any date here are some fake

mydf<-expand.grid(1:10,letters[1:3])
mydf$rnum<-rnorm(30)
mydf
   Var1 Var2        rnum
1     1    a  0.35928359
2     2    a  0.27431573
3     3    a  0.22948381
4     4    a -1.31041870
5     5    a  2.57832871
6     6    a  0.10697714
....................

29    9    c -0.33768297
30   10    c  0.85797343

To add mean and sd

mydf$m<-ave(dmydf$rnum, dmydf$Var2, FUN=mean)
dmydf$sd<-ave(dmydf$rnum, dmydf$Var2, FUN=sd)
AFAIK no. But you can store output values in list/vector/matrix/data frame so you can get more results in one return statement.

Regards
Petr