I have a question regarding the most efficient way to select a substring of a vector: I have a vector of value v, and I want to select a subspace of this vector called w such that: w=v[1:n] where sum(w) = x I am interested in what you thing would be the most efficient way to do this - I would like to avoid slowing down my simulations as much as possible. Thank you very much for any help that anyone is able to give. [[alternative HTML version deleted]]
Hi Benjamin, There may be faster ways, but v <- 1:100 x <- 10 n <- which(cumsum(v) == x) w <- v[1:n] seems pretty straightforward. Best, Ista On Wed, Mar 2, 2011 at 10:42 AM, Benjamin Hartley <benhartley903 at googlemail.com> wrote:> I have a question regarding the most efficient way to select a substring of > a vector: > > I have a vector of value v, and I want to select a subspace of this vector > called w such that: > > w=v[1:n] > > where > > sum(w) = x > > I am interested in what you thing would be the most efficient way to do this > - I would like to avoid slowing down my simulations as much as possible. > > Thank you very much for any help that anyone is able to give. > > ? ? ? ?[[alternative HTML version deleted]] > > ______________________________________________ > R-help at 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. >-- Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org
Is this what you want? I don't know what your v looks like, but this
won't
work if there are cases in which v won't sum to exactly x.
x <- 20
v <- sample(0:1, 100, T)
w <- v[1:which(cumsum(v)==x)]
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r-help-bounces at r-project.org wrote on 03/02/2011 10:42:12 AM:
> [image removed]
>
> [R] Vector manipulations
>
> Benjamin Hartley
>
> to:
>
> r-help
>
> 03/02/2011 11:08 AM
>
> Sent by:
>
> r-help-bounces at r-project.org
>
> I have a question regarding the most efficient way to select a substring
of> a vector:
>
> I have a vector of value v, and I want to select a subspace of this
vector> called w such that:
>
> w=v[1:n]
>
> where
>
> sum(w) = x
>
> I am interested in what you thing would be the most efficient way to do
this> - I would like to avoid slowing down my simulations as much as possible.
>
> Thank you very much for any help that anyone is able to give.
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at 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.