[R] problem with a function

David Winsemius dwinsemius at comcast.net
Fri May 28 18:37:27 CEST 2010

On May 28, 2010, at 12:03 PM, Sarah Goslee wrote:

>> From your code:
> mean <- c(rep(mu0, mzero), rep(mu1,m-mzero))
> mean() is a function. If you overwrite it with data, you may mess
> other things up -
> any function you call that calls mean will now fail (at best).

Actually, it's bad but not quite that bad.

 > mean <- c(1,2,3,4)
 > mean(1:10)
[1] 5.5
 > mean(mean)
[1] 2.5
 > mean[3]
[1] 3
 > mean
[1] 1 2 3 4

 > apply(matrix(1:100, ncol=10),1, mean)
  [1] 46 47 48 49 50 51 52 53 54 55
 > rm(mean)  # the interpreter "knows" to only remove the vector object
 > mean
function (x, ...)
<environment: namespace:base>
 > rm(mean)  # and will refuse to remove the base function
Warning message:
In rm(mean) : object 'mean' not found

Generally the interpreter can tell when a name is being intended as a  
function. Certainly when () follows the name, a function will be  
sought and other objects with identical names ignored.There are  
exceptions to that statement and your point is very well taken, but  
the main level of confusion is in the human brain rather than the R- 
interpreter. There used to be more partial name matching, but my  
reading of the NEWS items makes me think there is a shift away from  
that facility.  Other functions that people often mis-use as object  
names, generally without obvious deleterious effects:

df  # the density of the F distribution

> var.f <- function(rho) {
>   (1-rho)*diag(m)+rho*J%*%t(J)
> }
> var.f() is a complete function, except that m and J are not passed
> as arguments. Instead, you rely on them being present in the
> calling environment, and that is both dangerous and bad practice.
> Sarah
> On Fri, May 28, 2010 at 12:00 PM, li li <hannah.hlx at gmail.com> wrote:
>> I am not sure about "overwrite mean() with data".  My purpose was
>> to generate random numbers that are from a multivariate normal
>> distribution with the mean vector.
>> For the var.f function, since I already specify m and J, so the only
>> variable is really rho, so I wrote it as a function of rho only.
>> Could you be a little more specific? Thanks a lot again.
>> 2010/5/28 Sarah Goslee <sarah.goslee at gmail.com>
>>> There are a bunch of problems in your code:
>>> you overwrite mean() with data, and that could screw things up.
>>> you have a function var.f that isn't passed all the arguments it  
>>> needs.
>>> est.4 is defined several times, each overwriting the previous.
>>> First you need to clean up these sorts of problems since they can
>>> lead to all kinds of bizarre results.
>>> Then, if you are still getting unexpected results, please send the  
>>> list
>>> a minimal example so that we can take a look.
>>> Sarah
> -- 
> Sarah Goslee
> http://www.functionaldiversity.org
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT

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