[R] newbie question: ROW average

[A Ezhil]

Hi,

Thank you all (Dimitris, Peter, Rolf, Gabor) for your
suggestions. I tried with all your suggestions. I am
getting different answers when I use:

rowsum(mat, gl(nrow(mat)/4, 4)) / 4 

and 

m.new <-
t(apply(array(t(m.old),dim=c(74,4,992/4)),c(1,3),mean))

When I tried with (assuming 'M' is my old matrix): 

dim(M) <- c(4,248,74)
mn <- apply(M, c(2,3), mean)

the following error occured:
Error: dim<- : dims [product 73408] do not match the
length of object [74]

When I manually checked the answers, it seems that 
rowsum(mat, gl(nrow(mat)/4, 4)) / 4 gives me the
correct answer. 

Thanks again for your time & suggestions.

Regards,
Ezhil




--- Dimitris Rizopoulos
<dimitris.rizopoulos at med.kuleuven.be> wrote:

> yes you're right; it was my mistake.
> 
> 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://med.kuleuven.be/biostat/
>     
>
http://www.student.kuleuven.be/~m0390867/dimitris.htm
> 
> 
> ----- Original Message ----- 
> From: "Rolf Turner" <rolf at math.unb.ca>
> To: <dimitris.rizopoulos at med.kuleuven.be>;
> <ezhil02 at yahoo.com>
> Cc: <r-help at stat.math.ethz.ch>
> Sent: Monday, May 29, 2006 1:55 PM
> Subject: Re: [R] newbie question: ROW average
> 
> 
> > Dimitris Rizopoulos wrote:
> > 
> >> look at ?rowMeans; you can also use "apply(mat,
> 1, mean)" but 
> >> rowMeans() is better.
> > 
> > By my reading of the question, this is not what
> > Ezhil wants.  He said:
> > 
> > ``I have a 992 x 74 matrix. I would like to form a
> new matrix
> >   by averaging each 4 rows from the original
> one.''
> > 
> > I.e. he wants (I think) the first row of the new
> matrix
> > to be the mean of the first 4 rows of the old one,
> the
> > second row of the new matrix to be the mean of
> rows 5
> > through 8 of the old one, and so on.
> > 
> > One way this could be done is via
> > 
> > > m.new <-
>
t(apply(array(t(m.old),dim=c(74,4,992/4)),c(1,3),mean))
> > 
> > cheers,
> > 
> > Rolf Turner
> > rolf at math.unb.ca
> >
> 
> Disclaimer:
> http://www.kuleuven.be/cwis/email_disclaimer.htm
> 
>