[igraph] Question related to R implementation

[Sylvain Loiseau]

Hi,

My question is perhaps not really related to the igraph library usage but  
rather to R. I'm curious to understand how the library is implemented. I'm  
particular, I'm wondering:

- How the vector of the object igraph.vs and igraph.es can be O-based? If  
I try :

  mode(V(g))

it answers :

  [1] "numeric"

It's probably usefull for linking with the C code, but how such a  
primitive R object as a vector can be redifined as being 0-based?

- I don't understand why the V(g) object can behave like a list (having  
"$" subscript: V(g)$name), if they are stored as vector.

- And a last question: what is this subscript syntax:

  V(g)[name == "foo"]

  Why don't we need to write

  V(g)[V(g)$name == "foo"]

  ?

Cheers,
Sylvain

--
Sylvain Loiseau
address@hidden
http://www.limsi.fr/~sloiseau

Fainéanter dans un monde neuf est la plus absorbante des occupations.

Nicolas Bouvier, /L'usage du monde/.