From berwin@maths.uwa.edu.au  Tue Aug  6 09:58:40 2002
From: berwin@maths.uwa.edu.au (berwin@maths.uwa.edu.au)
Date: Tue, 6 Aug 2002 10:58:40 +0200 (MET DST)
Subject: You requested this report (PR#1880)
Message-ID: <200208060858.KAA21847@pubhealth.ku.dk>

Hi guys,

I am planning to let my students do some simulations regarding the
bias of the sample standard deviation.  The following function is
pretty standard (so I hope :) ):

> sim <- function(nrng, replic, true.s, random, ...){
+   res <- NULL
+   for(n in nrng){
+     data <- matrix(random(n*replic,...), ncol=replic)
+     val <- sqrt(apply(data, 2, var))
+     res <- rbind(res,
+                  cbind(bias=val-true.s, n=n))
+   }
+   res
+ }

It takes a vector of sample sizes, a number (the number of
replications we want to simulate), the true value of the standard
deviation and a function that generates the random number (which may
depend on additional paramters).  So let's try this:

> nrng <- c(2,4,8,16,32,64)
> replic <- 500
> true.s <- 2
> tmp <- sim(nrng, replic, true.s, rnorm, sd = 2)

Yes, seems to work.  Now I thought of perhaps creating a list of
several scenarios (random numbers) and loop over it.  So I tried:

> dist <- list(list(rnorm, true.s = 2, sd=2),
+              list(rexp, true.s = 1)
+              )

Followed by

> res <- sim(nrng, replic, dist[[1]][2], dist[[1]][1], dist[[1]][-c(1,2)])
Error in as.vector(data) : couldn't find function "random"

O.k., this doesn't work.  So let us try:

> res <- sim(nrng, replic, dist[[1]][2], as.function(dist[[1]][1]), dist[[1]][-c(1,2)])
Error in as.function.default(dist[[1]][1]) : 
        invalid body argument for "function"
Should NEVER happen; please bug.report() [mkCLOSXP]

No idea why you consider this a bug. :)  I would have been willing to
put it down to my misuse of R.  But since you requested a bug report,
here it is.

Cheers,

        Berwin

BTW:  How can I actually do what I want to do?  I realise that I am
probably on a completely wrong track regarding the passing of the
... parameters.

--please do not edit the information below--

Version:
 platform = i686-pc-linux-gnu
 arch = i686
 os = linux-gnu
 system = i686, linux-gnu
 status = 
 major = 1
 minor = 5.1
 year = 2002
 month = 06
 day = 17
 language = R

Search Path:
 .GlobalEnv, package:ctest, Autoloads, package:base


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You requested this report (PR#1880)
berwin@maths.uwa.edu.au