average among one factor in a nested dataframe

Hi Junquian:

I try your code (there is a typo, I believe)

a<-rnorm(6)
b<-rnorm(9)
f1<-c("x1","x2","x3")
f2<-c("y1","y2")
id<-c(1:6)
a_df<-data.frame(cbind(id,f1,"y1",a))
id<-c(1:9)
b_df<-data.frame(cbind(id,f1,"y2",b))

But I don't understand the "nested" databases.
I see that both have f1 variable but I do not see f2 variable in any of
them. So, what do you mean with "collapse f2"?

Maybe you need to first "merge()" de databases and then "aggregate()"
them.

Have a nice day!

El dom, 24-04-2011 a las 23:42 -0500, Junqian Gordon Xu escribi?:

I have two nested data frames:

a<-rnorm(6)
b<-rnorm(9)
f1<-c("x1","x2","x3"))
f2<-c("y1","y2")
id<-c(1:6)
a_df<-data.frame(cbind(id,f1,"y1",a))
id<-c(1:9)
b_df<-data.frame(cbind(id,f1,"y2",b))

I want to preserve id and f1, but want to collapse f2 and take the
corresponding mean values of a and b. Missing value in either dataframe
should be handled properly (i.e., just take the non-missing number
without dividing by 2).

I had a look at rowSum/Means and s/l/tapply, but couldn't figure out how
to handle this case cleanly. Any suggestions?

Thanks
Gordon