Hello Professor Ripely, Sorry for not being clear. I posted after a long day of struggling. Also my toy distance matrix should have been symmetrical.
Simply put I have spatially autocorrelated data collected from many points. I would like to do a linear regression on these data. To deal with the autocrrelation I want to resample a subset of my data with replacement but I need to restrict subsets such that no two locations where data was collected are closer than Xm apart (further apart than the autocrrelation in the data). Thanks for having a look at this for me. I will look up the hard-core spatial point process. Grant 2008/9/4 Prof Brian Ripley <[EMAIL PROTECTED]> > I see nothing here to do with the 'bootstrap', which is sampling with > replacement. > > Do you know what you mean exactly by 'randomly sample'? In general the way > to so this is to sample randomly (uniformly, whatever) and reject samples > that do not meet your restriction. For some restrictions there are more > efficient algorithms, but I don't understand yours. (What are the 'rows'? > Do you want to sample rows in space or xy locations? How come 'dist' is > not symmetric?) For some restrictions, an MCMC sampling scheme is needed, > the hard-core spatial point process being a related example. > > > On Wed, 3 Sep 2008, Grant Gillis wrote: > > Hello List, >> >> I am not sure that I have the correct terminology here (restricted >> bootstrap) which may be hampering my archive searches. I have quite a >> large >> spatially autocorrelated data set. I have xy coordinates and the >> corresponding pairwise distance matrix (metres) for each row. I would >> like >> to randomly sample some number of rows but restricting samples such that >> the >> distance between them is larger than the threshold of autocorrelation. I >> have been been unsuccessfully trying to link the 'sample' function to >> values >> in the distance matrix. >> >> My end goal is to randomly sample M thousand rows of data N thousand times >> calculating linear regression coefficients for each sample but am stuck on >> taking the initial sample. I believe I can figure out the rest. >> >> >> Example Question >> >> I would like to radomly sample 3 rows further but withe the restriction >> that >> they are greater than 100m apart >> >> example data: >> main data: >> >> y<- c(1, 2, 9, 5, 6) >> x<-c( 1, 3, 5, 7, 9) >> z<-c(2, 4, 6, 8, 10) >> a<-c(3, 9, 6, 4 ,4) >> >> maindata<-cbind(y, x, z, a) >> >> y x x a >> [1,] 1 1 1 3 >> [2,] 2 3 3 9 >> [3,] 9 5 5 6 >> [4,] 5 7 7 4 >> [5,] 6 9 9 4 >> >> distance matrix: >> row1<-c(0, 123, 567, 89) >> row2<-c(98, 0, 345, 543) >> row3<-c(765, 90, 0, 987) >> row4<-c(654, 8, 99, 0) >> >> dist<-rbind(row1, row2, row3, row4) >> >> [,1] [,2] [,3] [,4] >> row1 0 123 567 89 >> row2 98 0 345 543 >> row3 765 90 0 987 >> row4 654 8 99 0 >> >> Thanks for all of the help in the past and now >> >> Cheers >> Grant >> >> [[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. >> >> > -- > Brian D. Ripley, [EMAIL PROTECTED] > Professor of Applied Statistics, > http://www.stats.ox.ac.uk/~ripley/<http://www.stats.ox.ac.uk/%7Eripley/> > University of Oxford, Tel: +44 1865 272861 (self) > 1 South Parks Road, +44 1865 272866 (PA) > Oxford OX1 3TG, UK Fax: +44 1865 272595 > [[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.
