Thanks Greg, that most definitely was it. So apparently the default is sampling without replacement. Fine, but this brings up a question I've had for a bit now, which is, how do you know what the default settings are for the arguments of any given function? The HTML help files don't seem to indicate in many (most) cases. Thanks.
> Try adding replace=TRUE to your call to sample, then you will get numbers > closer to what you are expecting. > > -- > Gregory (Greg) L. Snow Ph.D. > Statistical Data Center > Intermountain Healthcare > greg.s...@imail.org > 801.408.8111 > > > > -----Original Message----- > > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > > project.org] On Behalf Of Jim Bouldin > > Sent: Thursday, July 23, 2009 12:00 PM > > To: r-help@r-project.org > > Subject: [R] Random # generator accuracy > > > > > > Dan Nordlund wrote: > > > > "It would be necessary to see the code for your 'brief test' before > > anyone > > could meaningfully comment on your results. But your results for a > > single > > test could have been a valid "random" result." > > > > I've re-created what I did below. The problem appears to be with the > > weighting process: the unweighted sample came out much closer to the > > actual > > than the weighted sample (>1% error) did. Comments? > > Jim > > > > > x > > [1] 1 2 3 4 5 6 7 8 9 10 11 12 > > > weights > > [1] 1 1 1 1 1 1 2 2 2 2 2 2 > > > > > a = mean(replicate(1000000,(sample(x, 3, prob = weights))));a # (1 > > million samples from x, of size 3, weighted by "weights"; the mean > > should > > be 7.50) > > [1] 7.406977 > > > 7.406977/7.5 > > [1] 0.987597 > > > > > b = mean(replicate(1000000,(sample(x, 3))));b # (1 million samples > > from > > x, of size 3, not weighted this time; the mean should be 6.50) > > [1] 6.501477 > > > 6.501477/6.5 > > [1] 1.000227 > > > > > > Jim Bouldin, PhD > > Research Ecologist > > Department of Plant Sciences, UC Davis > > Davis CA, 95616 > > 530-554-1740 > > > > ______________________________________________ > > 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. > Jim Bouldin, PhD Research Ecologist Department of Plant Sciences, UC Davis Davis CA, 95616 530-554-1740 ______________________________________________ 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.
