[R] aggregate, by tapply

[Frank E Harrell Jr]

In the soon-to-be beta-released Hmisc library, you can do this with the summarize function (attached) in the following way:

summarize(cbind(y,weights), groups, function(x)g(x[,1],x[,2]))

I have attached code for summarize.  Also, Hmisc has several functions for weighted estimators. -Frank Harrell

On Thu, 24 Jan 2002 07:56:59 +0100
Petr Pikal <petr.pikal at precheza.cz> wrote:

> 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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-- 
Frank E Harrell Jr              Prof. of Biostatistics & Statistics
Div. of Biostatistics & Epidem. Dept. of Health Evaluation Sciences
U. Virginia School of Medicine  http://hesweb1.med.virginia.edu/biostat
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