Re: [igraph] Simplify sums up weights in dev version 0.6-1899 ?

[Tamas Nepusz]

> In stable version of igraph these commands transform graph with multiple 
> edges into weighted graph:
> 
> E(g2)$weight<-count.multiple(g2)
> g2=simplify(g2)
> 
> But not in igraph_nightly_0.6-1899-20100505. It's like this because new 
> simplify() apart from removing multiple edges it also sums up weights of 
> those edges and put them all into the edge left.
> 
> Is it intentional or a bug? How can I create weighted graph in dev version?
It is intentional and part of some of the changes in attribute handling that we 
will roll out in igraph 0.6. In particular, you will be able to define 
"combining functions" for attributes that tell igraph how to infer the 
attributes of edges in the new graph that are merged from multiple edges in the 
old graph. The same will apply to vertices as well. It looks like "sum" is the 
default combining function in the R interface now. The solution is simple:

E(g2)$weight <- 1
g2 = simplify(g2)

-- 
T.