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Re: [igraph] vertex ids and function igraph_vcount(const igraph_t *graph

From: Tamas Nepusz
Subject: Re: [igraph] vertex ids and function igraph_vcount(const igraph_t *graph)
Date: Fri, 7 Aug 2009 22:23:26 +0100

Hi Christian,

Hello everybody
   if you have a graph with six edges like this:
How many memory is reserved for the vertex vector? --> 4 or 30000000 positions?

30000000. igraph graphs have numeric vertex IDs starting from zero and they are always continuous. The code you sent creates a graph for you that has 30000000 vertices and most of them are isolated (they have no edges). If you need only 4, you have to create a mapping from your numeric IDs to the range [0; 3], remap the vertex IDs in the edges vector to this range and possibly add the original numeric IDs as a numeric attribute to the vertices if you need them later. For more information on using attributes from the C core, see the following page:



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