Re: [igraph] going from a directed to an undirected graph

[Tamas Nepusz]

Dear Alisa,

> My problem is that when I used the as.undirected function with the  
> "collapse" parameter, I wiped out the secondary connection. Is there  
> any way to replace each pair of directed edges with one undirected  
> edge (i.e. not the "each" parameter) without removing multiple  
> edges? Suggestions?
I assume you are using the R interface of igraph. Try utilizing the  
simplify() and count.multiple() calls. A possible solution is listed  
in the documentation:

E(g)$weight <- count.multiple(g)
g <- simplify(g)
E(g)$weight

simplify eliminates all multiple edges, so you'll have at most one  
edge from a->b or b->a. However, its associated weight attribute will  
contain the number of edges that were collapsed into this single edge.

--
T.