[R] labels of a conditioning variable in xyplot

[Nathan Leon Pace, MD, MStat]

I am running R 2.1.1 on a Mac g5 under Mac OS 10.4.2.

I have an xyplot with a single conditioning variable (8 levels) .

Here is the code for the conditioning variable used in the formula  
argument of xyplot:

       factor(
         drugauthoryear,
         levels = c(
           'bupicapogna1999',
           'levobenhamou2003',
           'ropicapogna1999',
           'ropipolley1999',
           'bupipolley1999',
           'levopolley2003',
           'ropibenhamou2003',
           'ropipolley2003'
         ),
         labels = c(
           'Bupi. Reference 2.',
           'Levo. Reference 4.',
           'Ropi. Reference 2.',
           'Ropi. Reference 3.',
           'Bupi. Reference 3.',
           'Levo. Reference 5.',
           'Ropi. Reference 4.',
           'Ropi. Reference 5.'
           )
       )


The object is not created and I get the following error message:

Error in do.call("pmax", lapply(cond, is.na)) :
     symbol print-name too long

When I delete the labels vector, the code runs without difficulty.

Any thoughts on this error message?

Thanks,

Nathan