[R] Summing up matrices in a list

[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
>