Re: [R] Summing up matrices in a list

From: Sundar Dorai-Raj <sundar.dorai-raj_at_pdf.com>
Date: Thu 17 Mar 2005 - 03:31:11 EST

Vicky Landsman wrote on 3/16/2005 10:21 AM:
> 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]]
>

Hi Vicky,

This question is in the archives several times:

http://finzi.psych.upenn.edu/R/Rhelp02a/archive/10963.html

My answer last time was the following:

m <- list(matrix(rnorm(4),2,2),

           matrix(rnorm(4),2,2),
           matrix(rnorm(4),2,2))

mexpr <- paste("m[[", seq(along = m), "]]", collapse="+") eval(parse(text = mexpr))

HTH, --sundar



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