I think you have calculated the wrong probabilities. Shouldn't it be > x <- c(2,2,6,2,1,1,1,3) > MASS::fractions(table(x)/length(x)) x 1 2 3 6 3/8 3/8 1/8 1/8 >
Yours sincerely / Med venlig hilsen Frede Aakmann Tøgersen Specialist, M.Sc., Ph.D. Plant Performance & Modeling Technology & Service Solutions T +45 9730 5135 M +45 2547 6050 fr...@vestas.com http://www.vestas.com Company reg. name: Vestas Wind Systems A/S This e-mail is subject to our e-mail disclaimer statement. Please refer to www.vestas.com/legal/notice If you have received this e-mail in error please contact the sender. > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] > On Behalf Of Nordlund, Dan (DSHS/RDA) > Sent: 10. april 2014 22:04 > To: Simone Gabbriellini; Rui Barradas > Cc: r-help@r-project.org > Subject: Re: [R] how to select an element from a vector based on a > probability > > > -----Original Message----- > > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > > project.org] On Behalf Of Simone Gabbriellini > > Sent: Thursday, April 10, 2014 11:59 AM > > To: Rui Barradas > > Cc: r-help@r-project.org > > Subject: Re: [R] how to select an element from a vector based on a > > probability > > > > Hello, Rui, > > > > it does, indeed! > > > > thanks, > > Simone > > > > 2014-04-10 20:55 GMT+02:00 Rui Barradas <ruipbarra...@sapo.pt>: > > > Hello, > > > > > > Use ?sample. > > > > > > sample(x, 1, prob = x) > > > > > Just be aware that, in using this method, the probability of selection of a > particular value will also be a function of how frequent the value is. For > example, > > set.seed(7632) > x <- c(2,2,6,2,1,1,1,3) > table(sample(x, 10000, prob=x, replace=TRUE)) > > 1 2 3 6 > 1664 3340 1696 3300 > > > The probability that a vector position with a value of 1 will be selected is > 1/18 > (in this particular example). However, the probability that a value of 1 > will be > selected is 1/6 since there are three 1's. The probability of selecting the > position with a value of 3 is 3/18. But since there is only one position > with a > value of 3, the probability of getting the value 1 on any given sample is > equal > to the probability of getting the value 3. > > > > > > > Hope this helps, > > > > > > Rui Barradas > > > > > > Em 10-04-2014 19:49, Simone Gabbriellini escreveu: > > > > > >> Hello List, > > >> > > >> I have an array like: > > >> > > >> c(4, 3, 5, 4, 2, 2, 2, 4, 2, 6, 6, 7, 5, 5, 5, 10, 10, 11, 10, > > >> 12, 10, 11, 9, 12, 10, 36, 35, 36, 36, 36, 35, 35, 36, 37, 35, > > >> 35, 38, 35, 38, 36, 37, 36, 36, 37, 36, 35, 35, 36, 36, 35, 35, > > >> 36, 35, 38, 35, 35, 35, 36, 35, 35, 35, 6, 5, 8, 6, 6, 7, 1, > > >> 7, 7, 8, 9, 7, 8, 7, 7, 13, 13, 13, 14, 13, 13, 13, 14, 14, 15, > > >> 15, 14, 13, 14, 39, 39, 39, 39, 39, 39, 41, 40, 39, 39, 39, 39, > > >> 40, 39, 39, 41, 41, 40, 39, 40, 41, 40, 41, 40, 40, 40, 39, 41, > > >> 39, 39, 39, 39, 40, 39, 39, 40, 40, 39, 39, 39, 1, 4, 3, 4) > > >> > > >> I would like to pick up an element with a probability proportional > > to > > >> the element value, thus higher values should be picked up more often > > >> than small values (i.e., picking up 38 should be more probable than > > >> picking up 3) > > >> > > >> Do you have any idea on how to code such a rich-get-richer > > mechanism? > > >> > > >> Best regards, > > >> Simone > > >> > > > > > > > > > > > Dan > > Daniel J. Nordlund, PhD > Research and Data Analysis Division > Services & Enterprise Support Administration > Washington State Department of Social and Health Services > > > ______________________________________________ > 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.
