On Tue, Dec 7, 2010 at 9:47 AM, Alexander Senger
<sen...@physik.hu-berlin.de> wrote:
> Hello,
>
>
> my data is contained in nested lists (which seems not necessarily to be
> the best approach). What I need is a fast way to get subsets from the data.
>
> An example:
>
> test <- list(list(a = 1, b = 2, c = 3), list(a = 4, b = 5, c = 6),
> list(a = 7, b = 8, c = 9))
>
> Now I would like to have all values in the named variables "a", that is
> the vector c(1, 4, 7). The best I could come up with is:
>
> val <- sapply(1:3, function (i) {test[[i]]$a})
>
> which is unfortunately not very fast. According to R-inferno this is due
> to the fact that apply and its derivates do looping in R rather than
> rely on C-subroutines as the common [-operator.
>
> Does someone now a trick to do the same as above with the faster
> built-in subsetting? Something like:
>
> test[<somesubsettingmagic>]
>
>This does not involve apply. You could time it to see if its any faster: > test.un <- unlist(test) > unname(test.un[names(test.un) == "a"]) [1] 1 4 7 -- Statistics & Software Consulting GKX Group, GKX Associates Inc. tel: 1-877-GKX-GROUP email: ggrothendieck at gmail.com ______________________________________________ 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.
