[R] barchart in trellis and NA

[Sigbert Klinke]

Hi,

I've a dataset with discrete data and several groups and in one group I 
have also missing values (NA). When I use table and barchart to 
visualize the counts I never get a bar for  NA in the barchart although 
it appears in the result of table. Is there a possibility to get this 
bar too?

Thanks in advance  Sigbert Klinke