Thanks Chuck. Ups, did not think of the problem in that way. That did exactly what I needed. I have another complication to this problem: I do not only have one vector of 1:1e^6 but several vectors of different length, say 5. Initially, my intervals are distributed over those 5 vectors and the ranges of those 5 vectors in a specific way (and you might have guessed by now that I would like to do something like a permutation test). Because I have this additional level, I guess I could do something like:
1)Sample the 5 vectors with probabilities proportional to the frequencies of the intial intervals on these vectors. 2)For each sampled vector: apply Chucks solution. ? Thanks a lot. Hadassa On Sun, Jul 19, 2009 at 11:13 PM, Charles C. Berry<cbe...@tajo.ucsd.edu> wrote: > On Sun, 19 Jul 2009, Hadassa Brunschwig wrote: > >> Hi >> >> I am not sure what you mean by sampling an index of a group of >> intervals. I will try to give an example: >> Let's assume I have a vector 1:1000000. Let's say I have 10 intervals >> of different but known length, say, >> c(4,6,11,2,8,14,7,2,18,32). For simulation purposes I have to sample >> those 10 intervals 1000 times. >> The requirement is, however, that they should be of those lengths and >> should not be overlapping. >> In short, I would like to obtain a 10x1000 matrix with sampled intervals. > > Something like this: > > >> lens <- c(4,6,11,2,8,14,7,2,18,32) >> perm.lens <- sample(lens) >> >> sort(sample(1e06-sum(lens)+length(lens),length(lens)))+cumsum(c(0,head(perm.lens,-1))) > > [1] 15424 261927 430276 445976 451069 546578 656123 890494 939714 969643 >> > > The vector above gives the starting points for the intervals whose lengths > are perm.lens. > > I'd bet every introductory combinatorics book has a problem or example in > which the expression for the number of ways in which K ordered objects can > be assigned to I groups consisting of n_i adjacent objects each is > constructed. The construction is along the lines of the calculation above. > > HTH, > > Chuck > > >> >> Thanks >> Hadassa >> >> On Sun, Jul 19, 2009 at 9:48 PM, David Winsemius<dwinsem...@comcast.net> >> wrote: >>> >>> On Jul 19, 2009, at 1:05 PM, Hadassa Brunschwig wrote: >>> >>>> Hi, >>>> >>>> I hope I am not repeating a question which has been posed already. >>>> I am trying to do the following in the most efficient way: >>>> I would like to sample from a finite (large) set of integers n >>>> non-overlapping >>>> intervals, where each interval i has a different, set length L_i >>>> (which is the number >>>> of integers in the interval). >>>> I had the idea to sample recursively on a vector with the already >>>> chosen intervals >>>> discarded but that seems to be too complicated. >>> >>> It might be ridiculously easy if you sampled on an index of a group of >>> intervals. >>> Why not pose the question in the form of example data.frames or other >>> classes of R objects? Specification of the desired output would be >>> essential. I think further specification of the sampling strategy would >>> also >>> help because I am unable to understand what sort of probability model you >>> are hoping to apply. >>> >>>> Any suggestions on that? >>>> >>>> Thanks a lot. >>>> >>>> Hadassa >>>> >>>> >>>> -- >>>> Hadassa Brunschwig >>>> PhD Student >>>> Department of Statistics >>> >>> >>> David Winsemius, MD >>> Heritage Laboratories >>> West Hartford, CT >>> >>> >> >> >> >> -- >> Hadassa Brunschwig >> PhD Student >> Department of Statistics >> The Hebrew University of Jerusalem >> http://www.stat.huji.ac.il >> >> ______________________________________________ >> 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. >> > > Charles C. Berry (858) 534-2098 > Dept of Family/Preventive > Medicine > E mailto:cbe...@tajo.ucsd.edu UC San Diego > http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901 > > > -- Hadassa Brunschwig PhD Student Department of Statistics The Hebrew University of Jerusalem http://www.stat.huji.ac.il ______________________________________________ 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.
