Hi Petr,
probably I don't understand correctly your question. However
you can write any function with several arguments (input variables) and
after use tapply. That is:

fn<-function(arg1, arg2, arg3, ....){....}
tapply(arg1, factor, fn, arg2, arg3,....)

Furthermore you can you the three dots "..." to pass any argument in the
functions in your fn()

Hope this helps you!
vito


----- Original Message -----
From: "Petr Pikal" <petr.pikal@precheza.cz>
To: <r-help@stat.math.ethz.ch>
Sent: Thursday, January 24, 2002 7:56 AM
Subject: [R] aggregate, by tapply


> 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@precheza.cz
> p.pik@volny.cz
>
>
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