[R] Dice simulation: Getting rep to re-evaluate sample()?

[Zembower, Kevin]

Thanks so much, Chuck and Mark. Here's my script to simulate 10,000
rolls of 100 fair dice to demonstrate their conformity to a normal
curve:
> x<-replicate(10000, sum(sample(1:6,100,replace=T)))
> sdx<-sd(x)
> sdx
[1] 17.13966
> meanx<-mean(x)
> meanx
[1] 350.0451
> hist(x, freq=FALSE)
> curve(dnorm(x, mean=meanx, sd=sdx), add=TRUE)
>

Thanks, again, for your quick and accurate help.

-Kevin

-----Original Message-----
From: Charles C. Berry [mailto:cberry at tajo.ucsd.edu] 
Sent: Monday, October 08, 2007 1:56 PM
To: Zembower, Kevin
Cc: R-help at stat.math.ethz.ch
Subject: Re: [R] Dice simulation: Getting rep to re-evaluate sample()?



See

 	?replicate

which I think is what you are after.

Chuck


On Mon, 8 Oct 2007, Zembower, Kevin wrote:

> I'm trying to get R to simulate the sum of the values on 10 fair dice
> (yes, it's related to a homework problem, but is not the problem
> itself). I tried to do this:
>> rep(sum(sample(1:6,100,replace=T)), times=10)
> [1] 341 341 341 341 341 341 341 341 341 341
>
> and noticed that sum(sample()) seems to be only evaluated once. How
can
> I overcome this, so that I get a vector of values that correspond to
> independent throws of 10 dice each time?
>
> Thanks for your advice and suggestions.
>
> -Kevin
>
> Kevin Zembower
> Internet Services Group manager
> Center for Communication Programs
> Bloomberg School of Public Health
> Johns Hopkins University
> 111 Market Place, Suite 310
> Baltimore, Maryland  21202
> 410-659-6139
>
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Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive
Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego
92093-0901