R help - Jan 2010 - How to calculate the row wise means for grouped columns in matrix?

Hi all,

 

I want to calculate the row wise mean of groups of columns in a matrix M. All
columns belonging to the same group have the same column name. My idea is to
create a new vector V containing these column names, but after first removing
the duplicates. Then I would calculate the means using for instance rowMean()
and by comparing the column names of M with the vector V, getting the indices of
the columns to use.

 

What do you think, is it a good idea or not? If yes, any suggestions how to do
it? If no, is there any alternative solution that might work better?

 

 

 

All the best,

 

Joel
 		 	   		  
_________________________________________________________________
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adapted from the help files of rowsum

x <- matrix(runif(100), ncol=5)
group <- sample(1:8, 20, TRUE)
xsum <- rowsum(x, group)
sweep(xsum, 1, table(group), "/")

or

aggregate(x, list(group), mean)[-1]

b

2010/1/15 Joel F?rstenberg-H?gg <joel_furstenberg_hagg at
hotmail.com>:
>
> Hi all,
>
>
>
> I want to calculate the row wise mean of groups of columns in a matrix M.
All columns belonging to the same group have the same column name. My idea is to
create a new vector V containing these column names, but after first removing
the duplicates. Then I would calculate the means using for instance rowMean()
and by comparing the column names of M with the vector V, getting the indices of
the columns to use.
>
>
>
> What do you think, is it a good idea or not? If yes, any suggestions how to
do it? If no, is there any alternative solution that might work better?
>
>
>
>
>
>
>
> All the best,
>
>
>
> Joel
>
> _________________________________________________________________
> Lagra alla dina foton p? Skydrive. Det ?r enkelt och s?kert!
> http://www.skydrive.live.com
>        [[alternative HTML version deleted]]
>
>
> ______________________________________________
> R-help at r-project.org 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.
>
>