[R] How to include NA's of a factor in table?

[Heinz Tuechler]

Dear All,

Is there a better way to include NA's of a factor in the output of table()
than using as.character()?
Admittedly, I do not understand the help page for table concerning the
exclude argument applied to factors. I tried in different ways, but could
not get NA to be included in the table, if not using as.character() (see
example).

Greetings,
Heinz

## example
fcv <- factor(c('a', NA, 'c'))
table(fcv)                # shows a, c
table(fcv, exclude='a')   # shows c
table(fcv, exclude="")    # shows a, c
table(fcv, exclude=NULL)  # shows a, c
table(as.character(fcv), exclude=NULL) # shows a, c, NA

platform       i386-pc-mingw32                          
arch           i386                                     
os             mingw32                                  
system         i386, mingw32                            
status         Patched                                  
major          2                                        
minor          3.1                                      
year           2006                                     
month          07                                       
day            01                                       
svn rev        38471                                    
language       R                                        
version.string Version 2.3.1 Patched (2006-07-01 r38471)