I prefer the function resample as it is given in the sample help, in this
way:

resample <- function(x, size, ...)
{
 if length(x <= 1) {if (!missing(size) && size == 0) x[FALSE] else x}
 else sample(x, size, ...)
}

Anyway, if an observation can not be twice in the sample, you have to use
replace=FALSE, this is, not replacement.

The solution of Thomas is very good, although you have to check if your data
is going to be in the matrix as rows vectors or columns vector. If the
former, user byrow=TRUE in the matrix function, if the later, thomas
solution is perfect.

Instead of using a for loop, I prefer:
t(replicate(100, resample(x, 9))) if you want a matrix where the vectors are
rows
or replicate(100, resample(x, 9)) if you want a matrix where the vectors are
columns.

So the program can be:

hist(rowMeans(replicate(100, resample(x, 9)))).

I hope this is useful for you!!

Thanks & Regards,
Pedro Canadilla
Oracle DBA


On 3/23/06, Thomas Petzoldt <thpe@hhbio.wasser.tu-dresden.de> wrote:
>
> Does the following what you want:
>
> x <- 1:100
> s <- matrix(0, nrow=200, ncol=9)
> for (i in 1:200) {
>   s[i, ] <- sample(x, 9)
> }
> m <- rowMeans(s)
> hist(m)
>
>
> The default behavior of sample is without replacement.
>
>
> Thomas
>
>
> Noam Friedman wrote:
> > > Hi all!
> > >
> > >
> > > I was wondering if you can help me with a little sampling issue I'm
> > > having in R.
> > >
> > > I have a database with 100 observations.
> > > I need to sample n=9 sample size, 200 times (i.e. get 200 samples of
> > > size 9).
> > > N (pop. size) =100
> > >
> > > Each sample can't contain the same observation more than one time
> > > (i.e. the program needs to check if the obs. has already been sampled
> > > into the sample - it it has, it should put it back and sample again
> > > another obs.)
> > >
> > > obviously  I need to do this with replacement.
> > >
> > > Then, I need to draw (I think the best is with a histogram) the
> > > distribution of the mean of each os the 200 samples.
> > >
> > > I guess I need to do a loop for the 'sample' function in R.
> > >
> > > I could really use your help.
> > >
> > >
> > > Regards,
> > >
> > >
> > > Noam Friedman.
> > >
> > > ______________________________________________
> > > R-help@stat.math.ethz.ch mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
>
> ______________________________________________
> R-help@stat.math.ethz.ch mailing list
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