[R] Summing up matrices in a list

[Marc Schwartz]

John,

That is correct. I took the example perhaps too literally, depending
upon what Vicky requires. If indeed the data structure is comprised of
>2 matrices, the approach using do.call() will not work.

Thanks for pointing that out.  I see that Adai had a similar idea.

Best regards,

Marc


On Wed, 2005-03-16 at 12:00 -0500, John Fox wrote:
> Dear Mark,
> 
> I believe that your solution won't work if there are more than two matrices
> to sum.
> 
> Regards,
>  John
> 
> --------------------------------
> John Fox
> Department of Sociology
> McMaster University
> Hamilton, Ontario
> Canada L8S 4M4
> 905-525-9140x23604
> http://socserv.mcmaster.ca/jfox 
> -------------------------------- 
> 
> > -----Original Message-----
> > From: r-help-bounces at stat.math.ethz.ch 
> > [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Marc Schwartz
> > Sent: Wednesday, March 16, 2005 11:30 AM
> > To: Vicky Landsman
> > Cc: R-Help
> > Subject: Re: [R] Summing up matrices in a list
> > 
> > On Wed, 2005-03-16 at 18:21 +0200, Vicky Landsman wrote:
> > > Dear all,
> > > I think that my question is very simple but I failed to solve it. 
> > > I have a list which elements are matrices like this:
> > >  
> > > >mylist
> > > [[1]]
> > >      [,1] [,2] [,3]
> > > [1,]    1    3    5
> > > [2,]    2    4    6
> > > 
> > > [[2]]
> > >      [,1] [,2] [,3]
> > > [1,]    7    9   11
> > > [2,]    8   10   12
> > > 
> > > I'd like to create a matrix M<-mylist[[1]]+mylist[[2]]
> > >      [,1] [,2] [,3]
> > > [1,]    8   12   16
> > > [2,]   10   14   18
> > > 
> > > Is there a way to create M without looping? 
> > > Thanks a lot,
> > 
> > 
> > > do.call("+", mylist)
> >      [,1] [,2] [,3]
> > [1,]    8   12   16
> > [2,]   10   14   18
> > 
> > See ?do.call for more information.
> > 
> > HTH,
> > 
> > Marc Schwartz
> > 
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