[R] programming questions

[Duncan Murdoch]

On 03/11/2010 2:05 PM, ivo welch wrote:
> quick programming questions.  I want to "turn on" more errors.  there
> are two traps I occasionally fall into.
>
> * I wonder why R thinks that a variable is always defined in a data frame.
>
>       >  is.defined(d)
>       [1] FALSE
>       >  d= data.frame( x=1:5, y=1:5 )
>       >  is.defined(d$z)
>       [1] TRUE
>       >  is.defined(nonexisting$garbage)
>       [1] TRUE
>
> this is a bit unfortunate for me, because subsequent errors become
> less clear.   right now, I need to do '(is.defined(d) and
> !is.null(d$z))' to check that my function inputs are valid.  It would
> be nicer if one could just write "if (is.defined(d$z)".
>
> * is there a way to turn off automatic recycling?  I would rather get
> an error than unexpected recycling.  I can force recycling with rep()
> when I need to.

Where did you find the is.defined() function?  It's not part of R.  The 
R function to do that is exists().

Duncan Murdoch