[R] sum

[Liaw, Andy]

> From: Peter Dalgaard BSA [mailto:p.dalgaard at biostat.ku.dk]
> 
> Barry Rowlingson <B.Rowlingson at lancaster.ac.uk> writes:
> 
> > Luis Silva wrote:
> > > Dear helpers
> > > I have a list where each element is a matrix (the list is obtained
> > > with lapply). I want to sum those matrices. Is there a function to
> > > do that? The sum function sums all the elements...
> 
> >   Here's a one-liner that converts your list into an array (by
> > unlisting it and then packing into an array with the right three
> > dimensions) and then runs apply(...,c(1,2),sum) to get the 
> answer you
> > want:
> 
> Didn't someone do an abind() function at some point? (Generalizing
> cbind/rbind) 

I believe there's an abind for Splus on StatLib, if I remember correctly by
Tony Plate & Rich Heiberger.  Do not believe it was made available for R,
though I believe it'd be very useful.

[snipped]
> However, aren't we ignoring the obvious?:
> 
> s<-0;(for(a in l)s<-s+a)

Indeed!  (I guess somehow the evil of for loops in the old S in deeply
engrained in some of us.)  Altough I like Sundar's version, too.

Cheers,
Andy


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