Thanks.
I wanted to avoid loops (even inside functions) because I thought they were
much slower than vector operations, and I really need an efficient code (not
an exercise!).
However, after a few tentatives I'm coming to the conclusion that loops are
actually MORE efficient (at least in the type of problem I'm working with).
Any thoughts on this?
Best regards,
Eduardo Horta
On Wed, Nov 17, 2010 at 3:42 PM, William Dunlap <wdun...@tibco.com> wrote:
> Don't fixate on avoiding loops. Bury them in a function
> so you don't have to see them and then you just want something
> that does the right thing quickly enough. (I'm assuming
> this is not a homework/puzzle type problem where you are not
> allowed to use loops). E.g., the following does the job (with
> no error checking):
> Ybar <- function(u, Y) {
> result <- Y[[1]](u)
> for(Yi in Y[-1]) result <- result + Yi(u)
> result/length(Y)
> }
>
> You could probably shoehorn this into a call to Reduce but there
> must be a for loop in Reduce.
>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
>
> ------------------------------
> *From:* Eduardo de Oliveira Horta [mailto:eduardo.oliveiraho...@gmail.com]
>
> *Sent:* Tuesday, November 16, 2010 4:15 PM
> *To:* David Winsemius
> *Cc:* Phil Spector; r-help@r-project.org; www...@gmail.com; William Dunlap
>
> *Subject:* Re: [R] Vectors out of lists?
>
> Thanks, guys... but it seems these suggestions won't work.
>
> Let me try to be more specific with a simple example:
>
> Y<-list()
> Y[[1]]<-function(u) sqrt(u)
> Y[[2]]<-function(u) sin(u)
> Y[[3]]<-function(u) 1/2*u
>
> I wanted something equivalent to
>
> Ybar<-function(u){
> 1/3*(Y[[1]](u) + Y[[2]](u) + Y[[3]](u))
> }
>
> but with arbitrary length(Y) and without using any loops. Also, I can't
> allow for discretization, since I must be able to evaluate Ybar at any u, as
> I'm going to integrate it with the function "integrate".
>
> Thanks again,
>
> Eduardo Horta
>
>
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