why is it numeric(0)?

 yea, I have read the help. But some one tell me that i f you want use a
vector that you don't know it's length, you should use xx=numric(0) ,

is it

not right? If it isn't right, how can I do?

It depends on the context.  Why do you need a vector, but don't know its
length?  Normally in a situation like that you'd just delay creating it
until you knew the length.

Duncan Murdoch