That's perfect, thanks a lot! Tonja Gesendet: Mittwoch, 10. Oktober 2012 um 21:37 Uhr Von: "William Dunlap" <[email protected]> An: "[email protected]" <[email protected]>, "[email protected]" <[email protected]> Betreff: RE: [R] own function: computing time Your original method would be the following function f <- function (x, y) { xy <- cbind(x, y) outside <- function(z) { !any(x > z[1] & y > z[2]) } j <- apply(xy, 1, outside) which(j) } and the following one quickly computes the same thing as the above as long as there are no repeated points (if there are repeated points it chooses one of them). f1 <- function (x, y) { o <- order(x, decreasing = TRUE) yo <- y[o] j <- logical(length(y)) j[o] <- yo == cummax(yo) which(j) } Think of the problem as finding the "ladder points" (Feller's term) of a sequence of points, the places where the sequence reaches a new high point. Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf > Of William Dunlap > Sent: Wednesday, October 10, 2012 9:52 AM > To: [email protected]; [email protected] > Subject: Re: [R] own function: computing time > > No, the desired points are not a subset of the convex hull. > E.g., x=c(0,1:5), y=c(0,1/(1:5)). > > Bill Dunlap > Spotfire, TIBCO Software > wdunlap tibco.com > > > > -----Original Message----- > > From: William Dunlap > > Sent: Wednesday, October 10, 2012 9:46 AM > > To: '[email protected]'; [email protected] > > Subject: RE: [R] own function: computing time > > > > Are the points you are looking for (those data points with no other data > > points above or to the right of them) a subset of the convex hull of the > > data points? If so, chull(x,y) can quickly give you the points on the convex > > hull (typically a fairly small number) and you can look through them for > > the ones you want. > > > > Bill Dunlap > > Spotfire, TIBCO Software > > wdunlap tibco.com > > > > > > > -----Original Message----- > > > From: [email protected] [mailto:[email protected]] On > Behalf > > > Of [email protected] > > > Sent: Wednesday, October 10, 2012 3:16 AM > > > To: [email protected] > > > Subject: [R] own function: computing time > > > > > > Hi all, > > > > > > I wrote a function that actually does what I want it to do, but it tends to be very slow > > for > > > large amount of data. On my computer it takes 5.37 seconds for 16000 data points > and > > > 21.95 seconds for 32000 data points. As my real data consists of 18000000 data > points > > it > > > would take ages to use the function as it is now. > > > Could someone help me to speed up the calculation? > > > > > > Thank you, Tonja > > > > > > system.time({ > > > x <- runif(32000) > > > y <- runif(32000) > > > > > > xy <- cbind(x,y) > > > > > > outer <- function(z){ > > > !any(x > z[1] & y > z[2])} > > > j <- apply(xy,1, outer) > > > > > > plot(x,y) > > > points(x[j],y[j],col="green") > > > > > > }) > > > > > > ______________________________________________ > > > [email protected] mailing list > > > [1]https://stat.ethz.ch/mailman/listinfo/r-help > > > PLEASE do read the posting guide [2]http://www.R-project.org/posting-guide.html > > > and provide commented, minimal, self-contained, reproducible code. > > ______________________________________________ > [email protected] mailing list > [3]https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide [4]http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code.
References 1. https://stat.ethz.ch/mailman/listinfo/r-help 2. http://www.R-project.org/posting-guide.html 3. https://stat.ethz.ch/mailman/listinfo/r-help 4. http://www.R-project.org/posting-guide.html ______________________________________________ [email protected] 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.
