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
Dimitris Rizopoulos
2010-Nov-25 14:44 UTC
[R] Applying function to elements of matrices in a list
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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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
>
--
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/