[R] two questions for R beginners

[Karl Ove Hufthammer]

On Mon, 1 Mar 2010 11:02:59 +0100 Karl Ove Hufthammer <karl at huftis.org> 
wrote:
> > * What were your biggest misconceptions or
> > stumbling blocks to getting up and running
> > with R?
> 
> Also I found it quite confusing that

One more thing that still trips me up sometimes. '$' works on data 
frames but not on matrices (with dimnames/colnames). Even though the two 
objects *look* exactly the same, '$' on one of them works while '$' on 
the other gives a *very* confusing error message. Example:

  d=head(iris[1:4])
  d2=as.matrix(d)
  
  d
  d2
  
  d$Sepal.Width
  d2$Sepal.Width

Some functions output matrices where you would expect them to output 
data frames, and then this problem occurs. (Is there a reason why '$' 
could/should not be made to 'work' on matrices too?)

-- 
Karl Ove Hufthammer