Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com
> -----Original Message----- > From: r-help-boun...@r-project.org > [mailto:r-help-boun...@r-project.org] On Behalf Of William Dunlap > Sent: Wednesday, November 17, 2010 9:42 AM > To: Eduardo de Oliveira Horta > Cc: r-help@r-project.org > Subject: Re: [R] Vectors out of lists? > > 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) > } Here is a comparison of using that Ybar in integrate() with one that involved a call to Vectorize (which loops over the elemenents of the input vector). The results are identical but the one without Vectorize is much faster. > Y<-list() > Y[[1]]<-function(u) sqrt(u) > Y[[2]]<-function(u) sin(u) > Y[[3]]<-function(u) 1/2*u > > Ybar0 <- function(u)mean(sapply(Y,function(fun)fun(u))) > integrate(Vectorize(Ybar0),0,1) 0.4587882 with absolute error < 5.6e-05 > Ybar1 <- function(u) { + result <- Y[[1]](u) + for(Yi in Y[-1]) result <- result + Yi(u) + result/length(Y) + } > integrate(Ybar1,0,1) 0.4587882 with absolute error < 5.6e-05 > system.time(for(i in 1:1000)integrate(Vectorize(Ybar0), 0, 1)) user system elapsed 18.39 0.00 18.43 > system.time(for(i in 1:1000)integrate(Ybar1, 0, 1)) user system elapsed 0.28 0.00 0.29 If some of your functions in Y were not vectorized then you would have to vectorize them. > 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 > > > > [[alternative HTML version deleted]] > > ______________________________________________ > 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. > ______________________________________________ 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.
