[R] factor or not factor that is a question

[Petr Pikal]

Dear all

I encountered strange problem with split factor. I tried to use

boxplot(split(aaaa, factor)) but I got an error message

> split(test$asar,kvartaly)
Error in split(x, f) : second argument must be a factor

> str(kvartaly)
 Factor w/ 8 levels "1Q.04","2Q.04",..: 1 1 1 1 1 1 1 1 1 1 ...
> str(test$asar)
 num [1:731] 16.8 16.6 16.6 16.4 16.7 ...
> is.factor(kvartaly)
[1] TRUE
****************************************

I used formula interface
boxplot(formula) which worked OK. 

What can be wrong with my factor kvartaly? Where to look? Why it is 
not accepted by split?

W2000
> version
         _              
platform i386-pc-mingw32
arch     i386           
os       mingw32        
system   i386, mingw32  
status                  
major    2              
minor    2.1            
year     2005           
month    12             
day      20             
svn rev  36812          
language R              
> 

Best regards.
Petr Pikal
petr.pikal at precheza.cz