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Re: [igraph] Question on max id node

From: Richard Geddes
Subject: Re: [igraph] Question on max id node
Date: Sun, 09 Mar 2008 18:22:42 -0400
User-agent: Thunderbird (X11/20080227)

Well, initially I imported an edgelist with

igraph_read_graph_edgelist(&graph, input_file, 0, false);

and ran

igraph_community_fastgreedy(&graph, NULL, &merges, &modularity);

and got normal results.

Then, to get at the graph attributes,  I attached the C attribute handler:


imported the edgelist with:

igraph_read_graph_ncol(&graph, input_file, NULL true, false, IGRAPH_UNDIRECTED);

and ran the community function on the graph and I get different results...

when importing with igraph_read_graph_edgelist, 11 nodes and 19 edges are reported are reported.. which is correct,
however when importing with the igraph_read_graph_ncol function, 19 nodes and 19 edges are reported.

Am I using igraph_read_graph_ncol correctly?


Richard Geddes wrote:
Thanks.  Looks like what I was looking for.

Tamas Nepusz wrote:
Hi Richard,

Is there a function that provides the value of the largest node id in
the imported graph?
If you are using C (I assume you do), try to attach the C attribute
handler and then read your graph using igraph_read_graph_ncol (this is
for the NCOL format which is practically a named edge list). This is
able to store the vertex names used in the NCOL file as a vertex
attribute. After that, you can scan the attribute values to find the
largest one.

See http://cneurocvs.rmki.kfki.hu/igraph/doc-0.5/html/ch09s02.html for
the usage of the C attribute handler.


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