Re: [igraph] basic graph construction

[Kurt J]

Great!  That makes sense...  Thanks so much for your quick response!

Now, for adding edge weights - the procedure is the same?

>>> g.add_edges((0,1))
>>> g.es[0]["weight"] = 89.99

Or is there a more appropriate container for edge weights?

-Kurt J

On Nov 20, 2007 4:38 PM, Tamas Nepusz <address@hidden> wrote:
> Hi Kurt,
>
> > >>> g = igraph.Graph(directed=True)
> > >>> g.add_vertices(1)
> >
> > Then how can i access that vertex object to add a UID attribute?  Or
> > is there a better way?
> You can use the vs attribute of the graph object to access the vertex set of
> the graph. vs usually behaves as a Python array, so to access the first vertex
> of the graph, you simply type g.vs[0]. The result of g.vs[0] is a Vertex
> object which usually behaves as a Python dict, so you can use the following:
>
> g.vs[0]["uid"] = "whatever"
> print g.vs[0]
>
> Mass-assignment is also possible (but I can't really remember whether it's
> available in igraph 0.4.4 or only in the development branch):
>
> g.vs["uid"] = ["list", "of", "uids", "to", "assign"]
>
> So, to access vertex attributes, you use g.vs[vertexindex][attributename] or
> g.vs[attributename]. Edge attributes are available as
> g.es[edgeindex][attributename].
>
> > Previously i was using networkx which had a nice syntax allowing each
> > node to be named as you want.
> The reason why it's implemented differently in igraph is because almost all
> relevant parts of igraph are written in C, but it's much easier in C to use
> numerical vertex/edge indices instead of names. The basic concept is that you
> refer to vertices and edges by index in igraph. If you want to look up a
> particular vertex by a given attribute, you can use:
>
> g.vs["attributename"].index("value_being_sought"]
>
> which returns the index of the vertex. If mass-assignment and mass-retrieval
> of attributes is not available yet in your build (I can't recall whether it's
> included in 0.4.4 or not, I'm using the dev branch :)), you can still use:
>
> g.get_vertex_attributes("attributename").index("value_being_sought")
>
> I hope this helped, if not, feel free to post again.
>
> Best,
> --
> T.
>
>
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