[R] tapply and weighted means

[Dimitris Rizopoulos]

you need also to split the 'w' column, for each level of 'x'; you 
could use:

lapply(split(truc, truc$x), function(z) weighted.mean(z$y, z$w))


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://www.med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm



----- Original Message ----- 
From: "Florent Bresson" <f_bresson at yahoo.fr>
To: "R-help" <r-help at stat.math.ethz.ch>
Sent: Thursday, January 12, 2006 3:44 PM
Subject: [R] tapply and weighted means


> I' m trying to compute weighted mean on different
> groups but it only returns NA. If I use the following
> data.frame truc:
>
> x  y  w
> 1  1  1
> 1  2  2
> 1  3  1
> 1  4  2
> 0  2  1
> 0  3  2
> 0  4  1
> 0  5  1
>
> where x is a factor, and then use the command :
>
> tapply(truc$y,list(truc$x),wtd.mean, weights=truc$w)
>
> I just get NA. What's the problem ? What can I do ?
>
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