Re: [igraph] Adding structure to empty graph

[Gábor Csárdi]

On Tue, Nov 3, 2009 at 4:12 PM, Andrew Conway <address@hidden> wrote:
> I would like to write a function that takes some edges data and adds it to a
> given graph, which starts as an graph.empty().  The edge data would be added
> iteratively, and at each iteration the edges are represented as a vector of
> characters, e.g. c('actor1','actor2').  These actors may or may not exist in
> the graph already.

igraph is in general not very good at this, since adding
vertices/edges are O(n+m) operations, but in terms of the total number
of vertices plus the total number of edges in the graph.

> I am having a hard time figuring out how to accomplish this in igraph.  It
> seems that igraph wants to generate some fixed number of vertices for a
> graph, then add structure.  Also, is it possible to add character vertices
> to graph objects, or does everything have to go through the V(g)$name
> attributions?

Internally igraph always uses numeric ids. If you want to use symbolic
ids, then you have to use attributes. It is not very hard, though. You
can easily write a function that check whether both vertices are in
the graph by calling match(newids, V(g)$name) and then add them if
they are not with add.vertices(..., attr=...). Then you just add the
edge with add.edges().

Best,
Gabor

> Any advice is greatly appreciated.
>
> ___________________________________
> Drew Conway
> Ph.D. Student
> Department of Politics, New York University
> address@hidden
> http://www.drewconway.com/zia
> @drewconway
>
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-- 
Gabor Csardi <address@hidden>     UNIL DGM