[R] Sampling in R

Sean Davis sdavis2 at mail.nih.gov
Thu Mar 23 12:31:00 CET 2006

On 3/23/06 5:52 AM, "Noam Friedman" <noamfrie at qos.net.il> 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.

That sounds correct.

> I could really use your help.

 x <- rnorm(100)
 meanvec <- vector()
 for (j in 1:200) {
   y <- sample(x,9)
   meanvec[j] <- mean(y)

If this example code doesn't get you started, then you will probably need to
be more specific about where you are getting stuck.


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