Message-ID: <3A822319EB35174CA3714066D590DCD5C4FA4C@usrymx25.merck.com>
Date: 2003-04-23T23:58:15Z
From: Liaw, Andy
Subject: sum
> 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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