function to include factors in summary data frame

Hi all,

I have a dataframe that includes data on individuals that are distributed
across multiple rows.  I have aggregated the data using ddply, but I have
columns in the original data frame that are factors ( such as sites "A",
"B", and "C") that I would like to include in the new data frame.  I have
done this in a clunky way using match() and a loop, but am wondering if
there is a more elegant approach.  Here is an example data set.

#Example
a<-c(rep(1:5,6)); b<-sort(b)
b<-c(rep("A",10),rep("B",10),rep("C",10))
a<-c(rep(1:5,6)); b<-sort(b)
d<-c(2008,2008,2009,2009,2010,2010);d<-rep(d,5)
e<-rnorm(30,2,1)
df<-data.frame(a,b,d,e) ; names(df)<-c("ind","site","year","height")

I created a new factor using ind and year, and would basically like to
include site in the new dataframe. Does anyone know how this could easily
be
done?

Thanks in advance.

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