Thank you all for your replys!

It is so much faster with rowsum(), thanks a million!
  Werner

Dimitris Rizopoulos <dimitris.rizopoulos@med.kuleuven.be> schrieb: probably you want ?rowsum(); 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: "Werner Wernersen" 

To: 
Sent: Friday, May 12, 2006 11:48 AM
Subject: [R] optimal way to compute matrix subtotals?


> Hi!
>
> I have large matrices, one column per variable and I have a vector 
> of factors / grouping symbols. Then I am computing subtotals for the 
> groups but it takes pretty long and thus I wanted to ask if there is 
> a better way to do it or if this is already the best way:
> subTotals <- function(x, groupvec) 
> do.call("rbind",lapply(split(x,groupvec),colSums,na.rm=T))
>
>
> Thanks reading my question and any hints!
> Werner
>
>
> ---------------------------------
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