Re: [R] optimal way to compute matrix subtotals?

From: Prof Brian Ripley <>
Date: Fri 12 May 2006 - 20:14:20 EST

On Fri, 12 May 2006, Werner Wernersen wrote:

> 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)

I suggest you look at rowsum (on a transpose of your matrix). It will not handle NAs, though, if you have any.

Brian D. Ripley,        
Professor of Applied Statistics,
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

______________________________________________ mailing list
PLEASE do read the posting guide!
Received on Fri May 12 20:17:42 2006

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.1.8, at Fri 12 May 2006 - 22:10:08 EST.

Mailing list information is available at Please read the posting guide before posting to the list.