[EMAIL PROTECTED] writes:
> I have found that specifying different "sizes" in the sample command has
> a funny effect on the random sampling. The code below is a condensed
> version of a function I wrote to simulate a bootstrap method. For
> simplicity, I eliminated the internal bootstrap loop, but kept a
> statement to draw one bootstrap sample, because this is where the
> problem occurs. The output (mean(y)^2) should be the same for the two
> runs of the function below, since it is based on the original rnorm
> draw. For the first iteration of this function, it is, but thereafter
> the results aren't the same. If I run this code in Splus, the results
> are the same. Also, if I set the size argument to be the same (or
> eliminate this line altogether), I get reproducible results.
What is the issue? To generate samples of different sizes, you may
need a different number of random draws, so the RNG is not going to be
in the same state the 2nd time you hit rnorm().
A current Splus (7.0.0) doesn't give you the same result either:
> test.fun(50,0,30,12345)
[1] 2.712664e-05 9.971680e-03
> test.fun(50,0,10,12345)
[1] 2.712664e-05 2.225859e-03
>
>
> I'm using R 2.2.0
>
>
>
> Thanks,
>
> -Lori
>
>
>
> test.fun<-function(nsamp, mu,q, seed, nsim=2){
>
> set.seed(seed)
>
> mnsq<-rep(NA,nsim)
>
> for (i in 1:nsim){
>
> y<-rnorm(nsamp,mean=mu)
>
> yboot<-sample(y, size=q, replace=T)
>
> mnsq[i]<-(mean(y)^2)
>
> }
>
> return(mnsq)
>
> }
>
>
>
> test.fun(50,0,30,12345)
>
> test.fun(50,0,10,12345)
>
>
>
> Lori E. Dodd, Ph.D.
>
> National Cancer Institute
>
> Biometric Research Branch
>
> 6130 Executive Blvd, MSC 7434
>
> Rockville, MD 20892
>
> (For overnight deliveries use 20852)
>
>
>
> Phone: 301-402-0383
>
> FAX: 301-402-0560
>
> Email: [EMAIL PROTECTED]
>
>
>
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
--
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907
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