[R] list structure question

[Liaw, Andy]

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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