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## Re: [igraph] How to transform nodes into (sub(graphs

 From: Tamás Nepusz Subject: Re: [igraph] How to transform nodes into (sub(graphs Date: Sat, 20 Jul 2013 23:07:04 +0200

```> I have written some code that goes through the nodes and makes a list
> of replacement graphs.  How can I now make a new graph h from these
> small graphs? My problem is that disjoint union will renumber the
> vertices making it hard to work out which nodes to connect to which.
It is not documented but disjoint union renumbers the vertices in order of
appearance. For example, let us assume that you are taking the disjoint union
of three graphs: G1, G2 and G3. G1 has V1 vertices, G2 has V2 and G3 has V3.
The result graph will have V1+V2+V3 vertices (of course); the first V1 vertices
(from vertex 0 to vertex V1-1) will belong to G1, vertices V1 to vertices
V1+V2-1 will belong to G2, and vertices V1+V2 to V1+V2+V3-1 will belong to G3.
Hope this helps in working out how your small graphs should be connected.

--
T.

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