sum of unknown number of matrices

try a simple for loop, it will be fast enough in this case, e.g.,

matSums <- function (lis) {
    out <- array(data = 0, dim = dim(lis[[1]]))
    for (i in seq(along = lis))
        out <- out + lis[[i]]
    out
}

a <- b <- c <- d <- matrix(1:4, 2, 2)
l <- list(a, b ,c, d)

matSums(l)


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Shubha Vishwanath Karanth" <shubhak at ambaresearch.com>
To: <r-help at stat.math.ethz.ch>
Sent: Wednesday, June 04, 2008 4:53 PM
Subject: [R] sum of unknown number of matrices

Hi R,



I have a list of matrices. I need to get the sum of all the matrices 
in
the list.



Example:

a=b=c=d=matrix(1:4,2,2)

l=list(a,b,c,d)





I need:

a+b+c+d

    [,1] [,2]

[1,]    4   12

[2,]    8   16



Something like do.call("+",l) is not working...why is this?





I may not be knowing the number of matrices in the list...



Thanks, Shubha



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