
I'd like to summarize several variables in a data frame, for multiple groups, and store the results in a data.frame. To do so, I'm using by(). For example:

df<-data.frame(a=1:10,b=11:20,c=21:30,grp1=c("x","y"),grp2=c("x","y"),grp3=c("x","y"))
dfsum<-by(df[c("a","b","c")], df[c("grp1","grp2","grp3")], range)

The result has a class of "by" and a mode of "list". I'm new to R and can't find any documentation on this class, and don't see methods for it associated with the as.data.frame.  How should I go about coercing this to a data frame?  Is there a comprehensive source that I'm might be missing, which can tell me such things?

Cheers
 		 	   		  
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