[R] help with tapply and weighted.mean

[Frank E Harrell Jr]

On Thu, 31 Jul 2003 22:00:13 +0400
Kosenkov Kirill <Kosenkov.Kirill at nac.spb.ru> wrote:

> Hello!
> 
> I have data frame with 'weights' in one of the columns. I need to 
> compute weighted mean on another column other factor variable and 
> i am trying to:
> 
> res<-tapply(data$k,list(data$model),weighted.mean,w=data$w,na.rm=T)
> 
> and i get:
> 
> 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
> 3: longer object length
> 	is not a multiple of shorter object length in: x * w
> 4: longer object length
> 	is not a multiple of shorter object length in: x * w
> 5: longer object length
> 	is not a multiple of shorter object length in: x * w
> 6: longer object length
> 	is not a multiple of shorter object length in: x * w
> 7: longer object length
> 	is not a multiple of shorter object length in: x * w
> 8: longer object length
> ....
> 
> What i am doing wrong? How i can pass vector of weights to the 
> 'weighted.mean' when using 'tapply'?
> 
> Thanks!
> 
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Here's an alternative that works.

install.packages('Hmisc')
library(Hmisc)
g <- function(y) wtd.mean(y[,1],y[,2])
summarize(cbind(y, wts), llist(stratvar1,stratvar2), g, stat.name='y')

llist is like list except it remembers the names of the arguments.  wtd.mean, llist, and summarize are in Hmisc.

---
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