RE: [R] list structure question

From: Liaw, Andy <andy_liaw_at_merck.com>
Date: Fri 02 Jul 2004 - 05:27:29 EST


Here's a test:

> n <- 1e4
> m <- 100
> x <- lapply(1:m, function(...) rnorm(n))
> gc(); system.time(ans1 <- rowMeans(as.data.frame(x)))

          used (Mb) gc trigger (Mb)
Ncells  432336 23.1     818163 43.7

Vcells 1125819 8.6 5012280 38.3
[1] 7.43 0.03 7.61 0.00 0.00
> gc(); system.time(ans2 <- rowMeans(do.call("cbind", x)))
          used (Mb) gc trigger (Mb)
Ncells  442338 23.7     818163 43.7

Vcells 1155810 8.9 6821883 52.1
[1] 0.03 0.00 0.03 0.00 0.00
> all(ans1 == ans2)

[1] TRUE HTH,
Andy

> From: Rajarshi Guha
>
> Hi,
> I have a list in which element is a vector (all of the same
> length and
> all numeric). I want to find the mean of the first elements of the
> vectors, the mean of the second elements of the vectors and so on.
>
> Currently I convert the list to a data.frame and apply rowMeans(). But
> is there a way to to do this directly on the list? I seem to recall a
> post in which there was such a function (or expression) but I
> just cant
> seem to find it.
>
> Could somebody point me in the right direction?
>
> -------------------------------------------------------------------
> Rajarshi Guha <rxg218_at_psu.edu> <http://jijo.cjb.net>
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R-help@stat.math.ethz.ch mailing list
https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Jul 02 05:31:02 2004

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