From: Gabor Grothendieck <ggrothendieck_at_gmail.com>

Date: Tue 10 Oct 2006 - 16:10:27 GMT

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Wed Oct 11 02:13:52 2006

Date: Tue 10 Oct 2006 - 16:10:27 GMT

Here are two ways:

f1 <- function(i) weighted.mean(X[i,1], X[i,2]) aggregate(list(wmean = 1:nrow(X)), as.data.frame(X[,3:5]), f1)

f2 <- function(x) data.frame(wmean = weighted.mean(x[,1], x[,2]), x[1, 3:5]) do.call(rbind, by(X, as.data.frame(X[,3:5]), f2))

Also you check out the na.rm= argument in ?weighted.mean which may or may not be relevant to you.

On 10/10/06, Young Cho <young.stat@gmail.com> wrote:

*> HI,
**>
*

> I am trying to figure out an efficient way to calculate group means and

*> associate each entry with it. I made up an example:
**>
**> A = rep(rep(0:1,each=2),3)
**> B = rep(rep(0:1,4),3)
**> C = rep(rep(c(0,0,1,1),2),3)
**> X =cbind(rnorm(24,0,1),runif(24,0,1),A,B,C)
**> A B C
**> [1,] -1.92926469 0.32213127 0 0 0
**> [2,] -0.83935617 0.77794096 0 1 0
**> [3,] -1.27799751 0.26276934 1 0 1
**>
**> Suppose I want to compute a weighted mean of X[,1] by for each group, which
**> is defined by unique vector (A,B,C) with weights are X[,2]. And then add a
**> column for the weighted group mean. How can I do this ? My matrix is fairly
**> large (few thousands) but, luckily, I have only a few factors (<10).
**>
**> Thanks a lot,
**>
**> Young.
**>
**> [[alternative HTML version deleted]]
**>
**> ______________________________________________
**> R-help@stat.math.ethz.ch mailing list
**> https://stat.ethz.ch/mailman/listinfo/r-help
**> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
**> and provide commented, minimal, self-contained, reproducible code.
**>
*

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Wed Oct 11 02:13:52 2006

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