task percentage completion

Dear All,

Is it possible to add a percentage completion bar to R? I find it
frustrating when running long calculations that I don't know at what point
the process is. It would be very helpful so I am not guessing if I should
wait a few minutes or hours.

I believe recent-ish versions of the plyr package include this
feature. Note, however, Prof Ripley's caution: it's not as trivial as
it might seem to do so _accurately_. With a bit of squinting, one
might even see the halting problem...

Obligatory: http://xkcd.com/612/

MW