[R] Adding two different factors to one observation?

[Florian Ahrweiler]

In a data frame, I would like to assign two or more factors to one 
observation. Is it possible? If so, how?

Example: In the variable $ dishes, there are several levels: "cup", 
"plate", "saucer". In my first observation, I see a saucer only. But in 
the second one, I see a cup and a saucer.  In the third, however, there 
is only a cup, in the fourth a plate only and so forth.

I'm an R beginner and I'll be grateful for any help.

Florian