R help - Mar 2011 - Element by element mean of a list of matrices

Hi All,
is there any effiective and dense/compact method to calculate the mean of a list
of - of course coincident - matrices on an element by element basis? The
resulting matrix' [i, j]-th element is the mean of the list's
matrices' [i, j]-th elements respectively...
Iterating by for statement is quite straightforward, but I am seeking for a more
elegant solution, and my attempt with the apply family of functions did not
work.

Thank you,
by
Peter

Peter,

as the matrices in the list have the same shape, you can unlist them 
into an array and then use rowMeans.

HTH

Claudia

Am 15.03.2011 21:17, schrieb hihi:
> Hi All,
> is there any effiective and dense/compact method to calculate the mean of a
list of - of course coincident - matrices on an element by element basis? The
resulting matrix' [i, j]-th element is the mean of the list's
matrices' [i, j]-th elements respectively...
> Iterating by for statement is quite straightforward, but I am seeking for a
more elegant solution, and my attempt with the apply family of functions did not
work.
>
> Thank you,
> by
> Peter
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Try this:

l <- list(matrix(rnorm(9), 3), matrix(rnorm(9), 3), matrix(rnorm(9), 3))
Reduce('+', l) / length(l)


On Tue, Mar 15, 2011 at 5:17 PM, hihi <v.p.mail@freemail.hu> wrote:
> Hi All,
> is there any effiective and dense/compact method to calculate the mean of a
> list of - of course coincident - matrices on an element by element basis?
> The resulting matrix' [i, j]-th element is the mean of the list's
matrices'
> [i, j]-th elements respectively...
> Iterating by for statement is quite straightforward, but I am seeking for a
> more elegant solution, and my attempt with the apply family of functions
did
> not work.
>
> Thank you,
> by
> Peter
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

	[[alternative HTML version deleted]]

On Tue, Mar 15, 2011 at 1:17 PM, hihi <v.p.mail at freemail.hu>
wrote:
> Hi All,
> is there any effiective and dense/compact method to calculate the mean of a
list of - of course coincident - matrices on an element by element basis? The
resulting matrix' [i, j]-th element is the mean of the list's
matrices' [i, j]-th elements respectively...
> Iterating by for statement is quite straightforward, but I am seeking for a
more elegant solution, and my attempt with the apply family of functions did not
work.
Hi,

in the package WGCNA (I'm the maintainer) we have functions pmean,
pmedian, pquantile etc. if you have your list of matrices in the
variable matList, you should be able to do something like

do.call(pmean, matList)

Example:


library(WGCNA)
a = matrix(c(1:9), 3, 3);
b = a + sample(c(-1, 1), 9, replace = TRUE);
matList = list(a=a, b=b);
do.call(pmean, matList)

results:
> a
     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9
> b
     [,1] [,2] [,3]
[1,]    0    5    8
[2,]    1    4    9
[3,]    4    7   10
> do.call(pmean, matList)
     [,1] [,2] [,3]
[1,]  0.5  4.5  7.5
[2,]  1.5  4.5  8.5
[3,]  3.5  6.5  9.5


HTH,

Peter

Thank you all, it will help :-)
Bye,
Peter