Re: [igraph] Collapsing/Folding graph based on vertex attributes

[S. M. Ali Abbas]

Hi Tamas,
Thanks a lot for your help. I highly appreciate it. This contract 
function, it seems has been introduced in Igraph 0.6.
I am struggling to apply the same on my graph. Specifically, I couldn't 
understand the mapping parameter in the function. The help page says 
that it should correspond to the elements of vertices. In my case, for 
instance, there are 57 unique ethnicities. That means the contracted 
graph, based on ethnicity vertex attribute, should have just 57 
vertices. Do I have to know vertex ID within each ethnicity, and then 
supply it here? This is how I (incorrectly) did it:

contracted_g <- contract.vertices(g, 
1:length(unique(V(g)$Ethnic.Group)), 
vertex.attr.comb=list(Ethnic.Group=toString, "ignore")) # just consider 
Ethnic group attribute, and ignore the rest for now.

As expected, I am getting this error:

At structural_properties.c:6915 : Invalid mapping vector length, Invalid 
value

Could you please shed more light how to do this mapping?

Thanks!

Cheers,
Ali


I unfortunately could not make it work for my graph. I am sorry but I am 
struggling to use this on my graph. The mapping parameter is

On 11/09/2012 15:05, Tamás Nepusz wrote:
> Hi,
>
> Use the contract.vertices() function first to contract the vertices, then use simplify() to collapse multiple edges between the 
> now-contracted vertices into a single one. These functions let you specify what to do with the attributes of the original 
> vertices and edges. For instance, if you want the new (contracted) vertices to have a "count" attribute that contains 
> the number of vertices they were contracted from, this can be achieved by adding a "count" attribute to every vertex of 
> the original graph with a value of 1 and then use vertex.attr.comb=list(count="sum") to specify that you want to sum 
> the "count" attributes while collapsing. Similarly, you can assign a "weight" of 1 to every edge before 
> calling simplify() and then sum the weight of the collapsed edges.