[R] How many random numbers needed?

[Birgit Lemcke]

Thank you Gavin.

I knew about the meaning set.seed for reproducability but  I did not  
realise that it is only the starting point.

Is it possible that very small or very big random numbers cause any  
kind of bias?

B.


Am 10.05.2008 um 14:50 schrieb Gavin Simpson:
> On Sat, 2008-05-10 at 13:21 +0200, Birgit Lemcke wrote:
>> Hello R-People!
>>
>> I am running R 2.7.0 on a Power Book (Tiger). (I am still R and
>> statistics beginner)
>>
>> Perhaps this is another stupid question of me, but I was wondering
>> how I know the needed random (set.seed) numbers, when running
>> randomForest (library randomForest) on a large dataset.
>
> The seed is just a starting point for the RNG. You can draw as many
> numbers as you like once the RNG has been seeded.
>
> The ability to set the seed allows repeated runs of functions like
> randomForest to provide the same results for each run. This is a basic
> requirement of reproducible research.
>
> require(randomForest)
> set.seed(1)
> mod1 <- randomForest(Species ~ ., data = iris)
> mod2 <- randomForest(Species ~ ., data = iris)
> set.seed(1)
> mod3 <- randomForest(Species ~ ., data = iris)
>
> all.equal(mod1, mod2)
> all.equal(mod1, mod3)
>
> You could put whatever (within reason - up to limits of an integer  
> in R)
> into the set.seed function, but the point is to provide the same  
> number
> in the seed if you want to make sure your results are reproducible.
>
> HTH
>
> G
>
>>
>> Thanks in advance
>>
>> Birgit
>>
>>
>>
>> Birgit Lemcke
>> Institut für Systematische Botanik
>> Zollikerstrasse 107
>> CH-8008 Zürich
>> Switzerland
>> Ph: +41 (0)44 634 8351
>> birgit.lemcke at systbot.uzh.ch
>>
>> 175 Jahre UZH
>> «staunen.erleben.begreifen. Naturwissenschaft zum Anfassen.»
>> MNF-Jubiläumsevent für gross und klein.
>> 19. April 2008, 10.00 Uhr bis 02.00 Uhr
>> Campus Irchel, Winterthurerstrasse 190, 8057 Zürich
>> Weitere Informationen http://www.175jahre.uzh.ch/naturwissenschaft
>>
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>> and provide commented, minimal, self-contained, reproducible code.
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Birgit Lemcke
Institut für Systematische Botanik
Zollikerstrasse 107
CH-8008 Zürich
Switzerland
Ph: +41 (0)44 634 8351
birgit.lemcke at systbot.uzh.ch

175 Jahre UZH
«staunen.erleben.begreifen. Naturwissenschaft zum Anfassen.»
MNF-Jubiläumsevent für gross und klein.
19. April 2008, 10.00 Uhr bis 02.00 Uhr
Campus Irchel, Winterthurerstrasse 190, 8057 Zürich
Weitere Informationen http://www.175jahre.uzh.ch/naturwissenschaft