[R] geneation

Keith.Jewell at campdenbri.co.uk Keith.Jewell at campdenbri.co.uk
Thu Feb 20 13:37:38 CET 2014

On 20/02/2014 12:00, (Ted Harding) wrote:> [see at end]
> It seems clear that Izhak seeks to detach the random generation of y
> from the random generation of x after using set.seed(). On my reading of
>    ?RNG
> once set.seed has been used, as RUI says, it affects all subsequent
> calls to the generator. Initially, however:
>    Note:
>    Initially, there is no seed; a new one is created from the current
>    time when one is required.  Hence, different sessions started at
>    (sufficiently) different times will give different simulation
>    results, by default.
> But, even so, it still seems (perhaps) that using a RNG without the
> call to set.seed() will still establish a seed (and its consequences)
> for that session (in effect there is an implicit call to set.seed()).
> This leads me to suggest that a useful innovation could be to add a
> feature to set.seed() so that
>    set.seed(NULL)
> (which currently generates an error) would undo the effect of any
> previous (explicit or implicit) call to set.seed() so that, for instance,
>    set.seed(100)
>    x<-10*runif(10)
>    set.seed(NULL)
>    y <- rnorm(10)
> would result in y being generated from a seed which was set from the
> system clock. There is no form of argument to set.seed() which instructs
> it to take its value from the system clock (or other sourc of external
> random events); and indeed it seems that only the system clock is available.


> For the time being (not having time just now) I leave the details
> to others ...
> Ted.
> -------------------------------------------------
> E-Mail: (Ted Harding) <Ted.Harding at wlandres.net>
> Date: 20-Feb-2014  Time: 12:00:07
> This message was sent by XFMail
Isn't your set.seed(NULL) the same as set.seed(as.integer(Sys.time())) ?

If so, I think Izhak can achieve his objective of reproducible random x and irreproducible random y with:
> set.seed(100)
> x<-10*runif(10)
> set.seed(as.integer(Sys.time()))
> y<-rnorm(10)

Keith Jewell - Statistician
Tel: +44 (0)1386 842055 (direct)
Email:  keith.jewell at campdenBRI.co.uk


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