On 10/10/2010 4:30 AM, Liviu Andronic wrote:
Hello
On Sun, Oct 10, 2010 at 1:16 AM, jim holtman <jholt...@gmail.com> wrote:
You need to set the set.seed yourself. There are some simulation
where I do want the same numbers generated and can use the set.seed to
set it to a know value. If you want something random each time, then
use the time of day in the call to set.seed.
I try to do this, but I get funny results. I put
try(rm(.Random.seed))
set.seed(Sys.time())
in
/usr/lib/R/etc/Rprofile.site
but I get the following error
Error in rm(.Random.seed) : cannot remove variables from base namespace
[Previously saved workspace restored]
and it is as if the set.seed() call didn't work, since I get the same
random values.
rnorm(1:10)
[1] -1.3618103 0.4241701 1.0720076 0.2208145 -0.5375314 -0.4846588
[7] 0.7576768 0.6527407 -0.6868786 0.8718527
If I do
set.seed(Sys.time())
rnorm(1:10)
[1] -0.6165650 0.6305187 -0.9316815 0.6034638 -0.8593514 -1.0243644
[7] -0.1050344 0.4408562 -0.3466161 0.4058430
manually, within the session, the seed seems to be changed as
requested. Am I doing something wrong?
The Rprofile.site is being executed before the saved workspace is
restored. See ?Startup for the sequence of events on startup. You could
put the rm() in .First() in the saved workspace and it would do what you
want.
But more generally, I would say the thing you are doing wrong is saving
.RData sometimes, but not consistently saving it. In my opinion it's
safest to never save it; then you won't recover unexpected things from
your history. But it's also safe to always save it. Then you'll get a
new copy of .Random.seed saved each time.
I think the q() function makes it a little too easy to do what you did:
if you intend to never save it, but answer "Yes" just once, you get
into your situation. I don't know what the alternative should be.
One possibility would be for R to record whether the workspace was
restored at the start of the session, and use that to determine the
default when ending it. But that would mess up people who are trying to
reproduce things from identical conditions, e.g. when tracking down a bug.
Duncan Murdoch
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