Are you taking the same online course as Barth Riley, who posed a very
similar question only this morning?
On Mar 24, 2011, at 11:07 AM, Hui Du wrote:
Hi All,
Suppose I have data like
b[[1]] = matrix(1:4, 2, 2)
b[[2]] = matrix(10:13, 2, 2)
b[[3]] = matrix(20:23, 2, 2)
[[1]]
[,1] [,2]
[1,] 1 3
[2,] 2 4
[[2]]
[,1] [,2]
[1,] 10 12
[2,] 11 13
[[3]]
[,1] [,2]
[1,] 20 22
[2,] 21 23
Now I want to calculate the mean of each cell across
the list. For example mean of (b[[1]][1,1], b[[2]][1,1], b[[3]]
[1,1]), mean of (b[[1]][1,2], b[[2]][1,2], b[[3]][1,2]) etc. e.g.
mean of (1, 10, 20), mean of(3, 12, 22). Could somebody tell me how
to do it? Thank you in advance.
> vec <- do.call("c", b) # turns values into a long vector
> dim(vec) <- c(length(b[[1]], length(b)) # "folds" it, so it is
three columns "wide"
> rowMeans(vec)
[1] 10.33333 11.33333 12.33333 13.33333
This is done in row-major order as are all of R's matrix operations,
so it's not exactly what you asked for, but you will need to get used
to row-first order if you're going to use R.
--
David Winsemius, MD
West Hartford, CT
______________________________________________
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.
