[R] hang-up during nlme call

[Gabor Grothendieck]

JJ <josh8912 <at> yahoo.com> writes:

: 
: Hello:
: I recently asked the list a question regarding
: warning.expression.  This is a different statement of
: the problem.  
: 
: I am doing a large simulation experiment using nlme
: and most of the data realizations run fine.  The
: simulations stall, however, on a few particularly
: noisy data sets.  What happens is that the nlme
: function initially calls the nlm function and some
: code in there generates an endless number of warning
: messages.  These are: "Warning: Singular precision
: matrix in level ...".  Becuse of this, my simulation
: is caught in an endless loop and after quite a while R
: crashes.
: 
: I do use try(nlme(...)), so if I could find a way to
: flag these warning and make them into errors, such as
: by calling stop(), then my code could move on to the
: next realizaton of the simulation.  Some warnings are
: produced that are not endless or otherwise
: problematic, so I do not want to cause an error for
: every warning.  
: 
: Does anyone have any ideas as to how to identify
: warning messages and call stop() or otherwise induce
: an error if the warnings are of a particular type?  

See ?withCallingHandlers .  Here is an example which raises an
error for an "X" warning but not other sorts of warnings.  

f <- function(x) if (x$message == "X") stop("X")
withCallingHandlers({
	print(10)
	warning("Y")  # this warning does not result in stop
	print(20)
	warning("X")  # this warning results in stop
	print(30)
}, warning = f)