Re: [igraph] calculating the number of edges on the boundary of S

[Fatemeh a]

Hi Tamas,

sorry for bothering you on this all again.

after the steps you explain to me ,I use the graph.strength()  to get the number of edges pointed out for each community, But I was wondering is it any way to assign  the id of each vertex  in the contracted graph exactly the membership number of the community in the original graph. as when we calculate the weighted degree of vertex 1 of the contracted graph, we will actually have the number of edges which pointed out of the community with the the membership number of 1 in the original graph.

thank you in advance,

Fatemeh

On Thu, Nov 27, 2014 at 1:36 PM, Tamás Nepusz <address@hidden> wrote:

Hi,

1. assign an edge weight of 1 to each edge

2. Use contract.vertices with the membership vector of your community structure to contract each community to a single vertex. Then simplify the graph and tell igraph to sum the edge weights when it merges multiple edges into a single one during simplification. 

3. The edge weights in the contracted graph will tell you rhe number of edges between the communities in the original graph.

T. 

On 25 Nov 2014, at 21:22, Fatemeh a <address@hidden> wrote:

Hi,

I would appreciate if some one could help me to speed up this piece of code  :

what I am trying to do is to calculate the number of edges on the boundary of community S but it is really slow.

numberofedge<-function(graph,community)

{ 

cs <- data.frame(combn(unique(membership(community)),2)) #----considering a combination of communities two by two

cx <- sapply(cs, function(x) {   #calculating edges in between two communities

    es<-E(graph)[V(graph)[membership(community)==x[1]] %--% 

              V(graph)[membership(community)==x[2]]] 

    length(es)})

y=cbind(t(cs),cx)

i=1                 

CS=array( data="" = length(unique(membership(community))))

while (i<length(y[,1])+1){    # calculating the edges on the boundary for each community

 CS[y[i,1]]=CS[y[i,1]]+y[i,3]

  CS[y[i,2]]=CS[y[i,2]]+y[i,3] 

  i=i+1

}

--

regards

F..A

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regards

F..A