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Re: [igraph] how to "simplify" a graph

From: Gábor Csárdi
Subject: Re: [igraph] how to "simplify" a graph
Date: Wed, 8 Aug 2012 10:19:14 -0400

On Mon, Aug 6, 2012 at 5:12 PM, Sam Steingold <address@hidden> wrote:
> (no, I am not asking about the simplify function)
> I have a directed graph with, say, 100 sources and 100,000 destinations,
> and only 5 sources which are also destinations.
> I am mostly interested in sources, but the destinations clutter
> everything.
> I want to "simplify" the graph by dropping all the destinations, but I
> want to add a "weighted" link between two sources which have common
> destinations.
> How do I do that?

I think what you might need is a bipartite projection. In a bipartite
(or two-mode) graph, you have two kind of vertices, e.g. sources and
destinations. When you create a one-mode projection, you create a
graph where two sources are connected if they have a common neighbor
among the destinations. (Or the other way.)

Check http://igraph.sourceforge.net/doc/R/bipartite.projection.html
The number of common neighbors of the two sources is automatically
added as an edge weight, if you set the multiplicity argument to TRUE
(the default).


> thanks!
> --
> Sam Steingold (http://sds.podval.org/) on Ubuntu 12.04 (precise) X 
> 11.0.11103000
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Gabor Csardi <address@hidden>     MTA KFKI RMKI

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