Summing up matrices in a list

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