I have a list of data frames like the following:

set.seed(123)
a<- data.frame(x=runif(10), y = runif(10), sample = seq(1,10))
b<- data.frame(x=runif(10), y = runif(10), sample = seq(1,10))
L<- list(a,b)

All data frames in the list have the same dimensions.  I need to calculate
the sample means for x and y.  The real data are lists of several thousand
quite large dataframes, so I need something that is pretty fast.  Here is
what I have so far:

y<- rowMeans(sapply(L,'[[','y'))
x<- rowMeans(sapply(L,'[[','x'))

this works great, but I'm only able to get the sample means for one column
at a time.  Is there a way to automate things a bit so that I can get the
sample means for several columns with one call?

Thanks for any suggestions,

Matthew

	[[alternative HTML version deleted]]

