RE: [igraph] igraph.community_fastgreedy method and isolated vertices

[venura.2.mendis]

Thanks for the help Tamas. When you mentioned non-simple graphs I
realised that I had multiple edges (That I didn't want) in my graph
everything worked fine even with the isolated nodes after I removed
them. If its helpful to have a graph with multiple edges I can send you
the data (let me know what format is best), however everything worked
fine for me once I fixed the bugs in my code.

Thanks,
Venura

-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf
Of Tamas Nepusz
Sent: 07 August 2008 15:47
To: Help for igraph users
Subject: Re: [igraph] igraph.community_fastgreedy method and isolated
vertices

Hi,

> its falling over. I suspect its because of isolated vertices (not
> connected to any other nodes) in my graph.
Graph.community_fastgreedy used to fail when executed on non-simple  
graphs or graphs with isolated vertices. Theoretically this bug is  
corrected in the dev tree (and will be corrected in the upcoming  
0.5.1). Anyway, if you could send me an example graph so I could test  
it in the dev tree, that would be great.

> I tried to remove them using the following code
Try this:

isolates = g.vs.select(_degree=0)
g.delete_vertices(isolates)

Your code didn't work because igraph reindexes the vertices when you  
delete one. Alternatively, you can collect isolate vertex indices  
first and delete them in one step:

isolates = [index for index, degree in enumerate(g.degree()) if degree  
== 0]
g.delete_vertices(isolates)

-- 
T.



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