Re: [igraph] how to add vertex and edge attributes

[Tamas Nepusz]

> suppose I have an attribute of a node, a label with the name of the  
> node, say  "simone"
>
> how can I retrive the index of the node with label == "simone"?
Every VertexSeq object has a .select() method that can be used to  
select a subset of the VertexSeq. Since g.vs is the set of all  
vertices in the graph, you can call .select() on g.vs as follows.  
Suppose that your attribute is "name" and the value you are looking  
for is "Simone". You can do the following:

g.vs.select(name="Simone") -- this returns a VertexSeq that contains  
ALL the vertices where the "name" attribute is "Simone". (The result  
is a VertexSeq and not a Vertex because theoretically there could be  
more than one vertex with this name). If you know that there is only  
one such vertex, you can type g.vs.select(name="Simone")[0] to get  
this single Vertex or g.vs.select(name="Simone")[0].index to get the  
index of this vertex.

Alternatively, you can get all the vertex names with g.vs["name"] and  
look for "Simone" using the .index() method of list objects:  
g.vs["name"].index("Simone") returns the index of the FIRST vertex  
whose name is "Simone".

--
Tamas