[R] Summing up matrices in a list

[Liaw, Andy]

Here's a slight variation:

> lst <- list(matrix(1:4, 2, 2), matrix(5:8, 2, 2), matrix(9:12, 2, 2))
> m <- matrix(0, 2, 2)
> m[] <- rowSums(do.call("cbind", lapply(lst, c)))
> m
     [,1] [,2]
[1,]   15   21
[2,]   18   24

This can probably be simplified even more with the `abind' package...

Andy

> From: Dimitris Rizopoulos
> 
> try this:
> 
> matSums <- function(lis, na.rm=FALSE){
>     if(!is.list(lis) || !all(sapply(lis, is.matrix))) 
> stop("'lis' must 
> be a list containing 2-dimensional arrays")
>     dims <- sapply(lis, dim)
>     n <- dims[1, 1]
>     p <- dims[2, 1]
>     if(!all(n == dims[1, ]) || !all(p == dims[2, ])) stop("the 
> matrices must have the same dimensions")
>     mat <- matrix(unlist(lis), n * p, length(lis))
>     matrix(rowSums(mat, na.rm=na.rm), n, p)
> }
> #########
> mylist <- list(matrix(1:6, 2), matrix(7:12, 2))
> matSums(mylist)
> 
> 
> I hope it helps.
> 
> Best,
> Dimitris
> 
> ----
> Dimitris Rizopoulos
> Ph.D. Student
> Biostatistical Centre
> School of Public Health
> Catholic University of Leuven
> 
> Address: Kapucijnenvoer 35, Leuven, Belgium
> Tel: +32/16/336899
> Fax: +32/16/337015
> Web: http://www.med.kuleuven.ac.be/biostat/
>      http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm
> 
> 
> ----- Original Message ----- 
> From: "Vicky Landsman" <msvika at mscc.huji.ac.il>
> To: <r-help at stat.math.ethz.ch>
> Sent: Wednesday, March 16, 2005 5:21 PM
> Subject: [R] Summing up matrices in a list
> 
> 
> > 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,
> > Vicky Landsman.
> > [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide! 
> > http://www.R-project.org/posting-guide.html
> >
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
> 
> 
>