R devel - Jun 2005 - sink() within a function?

sink() isn't behaving as i expect, when used inside a function, eg:
   x<-data.frame(F=c("O","O"))
   f<-"foo.txt"
   sink(f); format(x); sink();   # foo.txt looks great!
   foo<-function(x,f) { sink(f); format(x); sink(); }
   foo(x,f=f) # foo.txt is empty!
why is this, and how can i successfully sink() within a function?

my real function does some rearrangement and formatting, but the above 
illustrates the problem i'm encountering.  thx in advance for any help! 
    [MacOS 10.3, R 2.0.1]

-- 
+--------------------------------------------------------------+
| Jon Stearley                  (505) 845-7571  (FAX 844-9297) |
| Sandia National Laboratories  Scalable Systems Integration   |
+--------------------------------------------------------------+

one more clue:
   library(debug); mtrace(foo); foo(x,f=f); ...  # foo.txt is not empty!

On Jun 1, 2005, at 10:23 AM, Rolf Turner wrote:
>
> foo<-function(x,f) { sink(f); print(format(x)); sink(); }
many thanks!  doh ;)

?format is unclear on return value imho.

-- 
-jon

Jon Stearley wrote:
> On Jun 1, 2005, at 11:22 AM, Duncan Murdoch wrote:
> 
>>     These functions convert their first argument to a vector (or
>>     array) of character strings which have a common format (as is done
>>     by 'print'), fulfilling 'length(format*(x, *)) ==
length(x)'.  The
>>     trimming with 'trim = TRUE' is useful when the strings are
to be
>>     used for plot 'axis' annotation.
> 
> 
> i saw this but
>    class(x)    # [1] "data.frame"
>    y<-format(x)
>    class(y)    # [1] "data.frame"
> confused me, let alone y<-as.character(format(x)).  i'm still an R 
> newbie...
> 
> 
>>I'll try to make it clearer.
> 
I think you've got a right to be confused, newbie or not.
format.data.frame() doesn't seem to follow the documentation, either 
before or after my change to the docs.  The result of format(x) is not a 
vector or array or even a data.frame of character strings, it's a 
data.frame of factors.

I'm not sure this is a reasonable thing to do.  Does anyone else have
an opinion on this?

My initial feeling is that format() on a data.frame should return a 
data.frame of character vectors, it shouldn't convert them to factors. 
One should be able to expect that format(x)[1,1] gives a character 
value, rather than the underlying factor encoding as it does in this 
example:

 > x <- data.frame(a=rnorm(5), b=rnorm(5))
 > y <- format(x, digits=3)
 > y
        a      b
1 -1.007 -0.525
2 -0.570  1.128
3  0.162  1.729
4 -1.642 -0.485
5  0.381  0.621
 > cat(y[1,1],"\n")
2

Duncan Murdoch