检测社区导致孤立的节点

Question

I am trying to gather some communities form my graph. However, the resulting communities consist of isolated nodes, which contradicts my understanding of communities. Here is my essential R/igraph-code:

g<-simplify(g)
print("isolates: ")
length(which(degree(g)==0)-1) # says 0

c<-fastgreedy.community(g)

cmem<-community.to.membership(g,c$merges,3081)
w<-which(cmem$membership==0)  
sub<-subgraph(g,w)

print("isolates in subgraph: ")
length(which(degree(sub)==0)-1) # says > 0

Did I make a mistake? Thank you for your help.

Answer 1

You have forgotten to subtract 1 from which(cmem$membership == 0) , which is required because igraph indexes the nodes from zero, while R uses a 1-based indexing. Try it again with w <- which(cmem$membership == 0) - 1 and see if the isolates persist.