[R] Two-argument functions in tapply()

[Peter Dalgaard BSA]

"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
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