R help - Feb 2006 - difference between rnorm(1000, 0, 1) and running rnorm(500, 0, 1) twice

Hi R users

This looks a simple question

Is there any difference between between rnorm(1000,0,1) and running 
rnorm(500,0,1) twice in terms of outcome ?

TM

Le 08.02.2006 04:21, Taka Matzmoto a ??crit :
>Hi R users
>
>This looks a simple question
>
>Is there any difference between between rnorm(1000,0,1) and running 
>rnorm(500,0,1) twice in terms of outcome ?
>
>TM
>  
>
Not here :

R> set.seed(1)
R> x <- rnorm(1000, 0, 1)
R> set.seed(1)
R> y <- rnorm(500, 0, 1)
R> z <- rnorm(500, 0, 1)
R> all(x == c(y,z))
[1] TRUE

Romain

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| Romain FRANCOIS - http://francoisromain.free.fr               |
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Romain Francois wrote:
> Le 08.02.2006 04:21, Taka Matzmoto a ??crit :
> 
> 
>>Hi R users
>>
>>This looks a simple question
>>
>>Is there any difference between between rnorm(1000,0,1) and running 
>>rnorm(500,0,1) twice in terms of outcome ?
>>
>>TM
>> 
>>
> 
> Not here :
> 
> R> set.seed(1)
> R> x <- rnorm(1000, 0, 1)
> R> set.seed(1)
> R> y <- rnorm(500, 0, 1)
> R> z <- rnorm(500, 0, 1)
> R> all(x == c(y,z))
> [1] TRUE
> 
> Romain
Indeed! The pseudo-random number generator is initialized at the same 
state, and thus, returns the same 1000 pseudo-random numbers in both 
cases. So, no differences.
Best,

Philippe Grosjean

Why don't you test it yourself?

E.g.,

set.seed(42)
bob1 <- rnorm(1000,0,1)
set.seed(42)
bob2 <- rnorm(500,0,1)
bob3 <- rnorm(500,0,1)
identical(bob1, c(bob2, bob3))

I won't tell you the answer. :-)

-- 
Bj??rn-Helge Mevik