try this:
Reduce("+", x) / length(x)
Best,
Dimitris
On 11/25/2010 3:42 PM, statmobile wrote:
Hello R-help,
Please cc me on all responses, as I only receive summary emails from
this list.
I'm wondering if anybody has any tips on how to accomplish this
efficiently. I have a list of matrices, and I'm trying to get the mean
of the [i,j]'th element of each matrix in a list.
So if I have a list of matrices, say
x <- list(a=matrix(rnorm(4),nrow=2),b=matrix(rnorm(4),nrow=2))
How would I get a 2x2 matrix, where the i,j'th element would be the mean
across the the list of each of the i,j'th elements in the list? That is,
where the [1,2] element would be the average of a[1,2] and b[1,2].
Of course my list and matrices are much larger, and I was hoping there
would be some trick with lapply that I may be missing here.
Thanks,
Brian
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--
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center
Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
Web: http://www.erasmusmc.nl/biostatistiek/
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