BTW, Ken Kleinman recently wrote a post on how to get a "real" random numbers (into R) from a web-service: http://www.r-bloggers.com/example-8-35-grab-true-not-pseudo-random-numbers-passing-api-urls-to-functions-or-macros/
<http://www.r-bloggers.com/example-8-35-grab-true-not-pseudo-random-numbers-passing-api-urls-to-functions-or-macros/> Cheers, Tal ----------------Contact Details:------------------------------------------------------- Contact me: tal.gal...@gmail.com | 972-52-7275845 Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) | www.r-statistics.com (English) ---------------------------------------------------------------------------------------------- On Fri, Apr 22, 2011 at 6:47 AM, Joshua Wiley <jwiley.ps...@gmail.com>wrote: > On Thu, Apr 21, 2011 at 8:34 PM, Penny Bilton <pennybil...@xnet.co.nz> > wrote: > > Hi Josh, > > > > Thanks for your reply. > > > > The problem is have is in trying to retain the proportions of 2 groups in > my > > data while sampling into training and test sets. I find that different > > arguments for set.seed give very different proportions of my 2 groups in > > the training and test sets. > > Sure, just because numbers are random does not guarantee that equal > numbers from both groups will be sampled. Perhaps you are looking for > some sort of constrained random sampling like sampling x from group 1 > and x from group 2? If so, try calling sample() separately on each > group (for help applying the same function to different groups, take a > look at ?by or ?tapply for example). > > Josh > > PS cced back to list > > > > > > > Penny. > > > > > > > > On 22/04/2011 3:27 p.m., Joshua Wiley wrote: > >> > >> Hi, > >> > >> On Thu, Apr 21, 2011 at 8:18 PM, Penny Bilton<pennybil...@xnet.co.nz> > >> wrote: > >>> > >>> I am using /set.seed()/ before the /sample/ function. > >>> > >>> How does the length of the argument of /set.seed()/ and order of the > >>> digits affect how the sampling is carried out? > >> > >> You can use set.seed() to specify a particular seed so that while > >> pseudo-random numbers are sampled, you can repeat it. For example: > >> > >> set.seed(10) > >> rnorm(10) > >> set.seed(10) > >> rnorm(10) > >> > >>> Specifically, I have used set.seed(123456789). Will this configuration > >>> give me a genuinely random sampling?? > >> > >> You will never get truly random sampling from a computer algorithm, > >> but it is darn close and more than adequate in the majority of cases. > >> 123456789 is just a length 1 vector containing the number 123456789, > >> not 9 separate numbers. > >> > >> Google will be able to give you a lot of information on pseudo-random > >> number algorithms as well as the concept of "seeds". Also see > >> ?set.seed > >> > >> Cheers, > >> > >> Josh > >> > >>> > >>> Thank you in anticipation. > >>> > >>> Penny. > >>> > >>> > >>> [[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. > >>> > >> > >> > > > > > > > > -- > Joshua Wiley > Ph.D. Student, Health Psychology > University of California, Los Angeles > http://www.joshuawiley.com/ > > ______________________________________________ > 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. > [[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.
