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## Re: [igraph] A question about Greedy community algorithm

 From: Tamas Nepusz Subject: Re: [igraph] A question about Greedy community algorithm Date: Thu, 12 Feb 2009 22:13:16 +0000

```After performing Community detection the resulting Dendogram
contains merges such as
(4834, 12676),
(5036, 12677),
(3744, 12329),
When there are only 12575
nodes.
what do 12677 these numbers indicate?
```
Let us assume that you have n nodes in your graph. This means that node indices go from 0 to n-1. Let us assume that you merge nodes i and j in the first step. When you merge them, the "virtual" node in which they got merged gets the next available node index; that is, index n. When you merge the next two nodes, the merged node becomes node #n+1, and so on. This is how you can get node indices larger than n. Or, in other words, as the documentation for the R package says:
```
```
"Each line is one merge and it is given by the ids of the two communities merged. The community ids are integer numbers starting from zero and the communities between zero and the number of vertices (N) minus one belong to individual vertices. The first line of the matrix gives the first merge, this merge creates community N, the number of vertices, the second merge creates community N+1, etc."
```
--
Tamas

```