to start with same seed:

set.seed(12345)

:-)

On Thu, May 21, 2009 at 1:22 AM, Daniel Nordlund <djnordlund@verizon.net>wrote:

> > -----Original Message-----
> > From: r-help-bounces@r-project.org
> > [mailto:r-help-bounces@r-project.org] On Behalf Of Peter Alspach
> > Sent: Wednesday, May 20, 2009 10:02 PM
> > To: milton ruser; Chloe Smith
> > Cc: r-help@r-project.org
> > Subject: Re: [R] Problems with sample variance
> >
> > Thanks Milton - I misread Chloe's original question.
> >
> > nSims <- 1000
> > sampSiz <- 15
> > myVars <- tapply(rnorm(nSims*sampSiz), rep(1:nSims, sampSiz), var)
> >
> > This is a little more succinct, although I do not know enough about
> > random number generation to be certain about the effect of breaking a
> > single call to rnorm into 1000 bits, rather than having 1000 calls to
> > rnorm (or even if there is such an effect.  Comment anyone?).
>
> It doesn't matter whether you use a single call or multiple calls, the same
> set of numbers will be generated either way (if one starts with the same
> seed).
>
> >
> > It used to be (and I imagine still is) not efficient
> > incrementally grow
> > an object in a loop [as is done in your code with variance.list <-
> > c(variance.list, var(mysample))].  Better to create
> > variance.list at its
> > full size first (filled with NA) and then populate it.  Not that it is
> > likely to make too much difference with these numbers.
> >
> > HTH .....
> >
> > Peter Alspach
>
> Hope this is helpful,
>
> Dan
>
> Daniel Nordlund
> Bothell, WA USA
>
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