[R] Two-argument functions in tapply()

[Rashid Nassar]

Just be careful using weighted.means() within tapply(), as the result may
not be what one might expect (I think because of the recycling rule, if I
remember correctly) if one hasn't thought it through. (I should think the
same may apply also to aggregate() ).

Rashid Nassar

On 22 Mar 2001, Peter Dalgaard BSA wrote:

> Date: 22 Mar 2001 16:04:53 +0100
> From: Peter Dalgaard BSA <p.dalgaard at biostat.ku.dk>
> To: Michal Bojanowski <buoy at wp.pl>
> Cc: R-project Mailing List <r-help at stat.math.ethz.ch>
> Subject: Re: [R] Two-argument functions in tapply()
> 
> "Michal Bojanowski" <buoy at wp.pl> writes:
> 
> > I wanted to compute a means of X weighted by W within groups defined by F
> > with the function below:
> > 
> > 	wmean <- function(x,w)
> > 		{
> > 		wm <- sum( x*w/sum(w) )
> > 		wm
> > 		}
> 
> (Now whatever was wrong with weighted.mean()??)
> 
> > used within tapply() function, like:
> > 
> > 	tapply(x,f,wmean,w=w)
> > 
> > but I received some values with 2 warnings:
> > 
> > 	Warning messages:
> > 	1: longer object length
> > 	        is not a multiple of shorter object length in: x * w
> > 	2: longer object length
> >       	  is not a multiple of shorter object length in: x * w
> > 
> > What is the right way to get the results (how to use 2-argument function in
> > tapply()), or maybe there is another simple way to do this
> 
> A couple of ways, none really pretty:
> 
> c(by(dataframe,f, function(d) evalq(wmean(x,w), d)))
> 
> or equivalently
> 
> c(by(dataframe,f, eval, expr=quote(wmean(x,w))))
> 
> or more directly
> 
> ind<-seq(along=x)
> tapply(ind, f, function(i) wmean(x[i],w[i]))
> 
> And of course
> 
> tapply(x*w, f, sum) / tapply(w, f, sum)
> -- 
>    O__  ---- Peter Dalgaard             Blegdamsvej 3  
>   c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
>  (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
> ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
> -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
> r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
> Send "info", "help", or "[un]subscribe"
> (in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
> _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
> 
> 
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._