I thought this was a good candidate for the plyr package, but it seems  
that l*ply functions are meant to operate only on separate list  
elements:

> Lists are the simplest type of input to deal with because they are  
> already naturally
> divided into pieces: the elements of the list. For this reason, the  
> l*ply functions don’t
> need an argument that describes how to break up the data structure.
> (from: plyr: divide and conquer, Hadley Wickham 2008)


  Perhaps a new case to consider?

   Best wishes,

baptiste




On 30 Dec 2008, at 15:33, Stephan Kolassa wrote:

> Dear useRs,
>
> I have a list, each entry of which is a matrix of constant dimensions.
> Is there a good way (i.e., not using a for loop) to apply a mean to  
> each
> matrix entry *across list entries*?
>
> Example:
>
> foo <- list(rbind(c(1,2,3),c(4,5,6)),rbind(c(7,8,9),c(10,11,12)))
> some.sort.of.apply(foo,FUN=mean)
>
> I'm looking for a componentwise mean across the two entries of foo,
> i.e., the following output:
>
>      [,1] [,2] [,3]
> [1,]    4    5    6
> [2

_____________________________

Baptiste Auguié

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag
______________________________


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