[R] aggregate, by tapply

[Petr Pikal]

Dear R users

I searched some sources but i did not find an answer.Please give 
me some hint to following problem.

I would like to compute a summary statistic for some vector for 
different factor levels. I know I can use tapply or aggregate but I 
do not know if there is a way how to use function with several 
(two) variable input (like weighted.mean).

I wrote a simple a function for factor weighted mean
fff<-function(x,fact,w)
{
ws<-tapply(w,fact,sum)
newx<-x*w
tapply(newx,fact,sum)/ws
}

which can handle particular case but does exist some more general 
solution how to use FUN(X1,X2) in aggregation procedures 
(tapply, aggregate, by) directly?

Thank you
Petr Pikal
petr.pikal at precheza.cz
p.pik at volny.cz


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