Hello,

simply create a membership vector (to each vertex its community number).
Example with 4 random communities:

library(igraph)
g<-erdos.renyi.game(100,3/100)
memb<-sample(1:4,100)
memb
  [1] 2 3 1 4 3 2 3 2 1 1 1 1 1 2 2 1 3 2 3 3 2 2 4 4 4 1 4 2 1 1 2 1 2 4 3 1 2
 [38] 4 4 3 3 2 4 2 4 3 2 1 1 1 2 3 1 3 1 4 1 2 1 2 1 1 1 2 3 3 1 1 1 3 4 3 3 3
 [75] 4 3 4 3 3 3 3 1 4 4 4 2 4 4 4 1 1 1 3 4 1 3 4 1 3 3
modularity(g,memb)
[1] 0.003766435

Best,
--
Fabio
 
> On 12 May 2015, at 23:33, Walter McHugh <[email protected]> wrote:
> 
> Hello,
> 
>    I am trying to compare network scale modularity scores for my network 
> using various community types.  The first types are what are generated 
> algorithmically, such as walktrap.  However, I would also like to assign each 
> vertex a community of my choosing and calculate modularity using the assigned 
> communities.  I have tried to do this by creating a vector that mimics the 
> output of running member() on a walktrap output.  The vector:
> 
> >> v = attrib$edgroup
> >> names(v) = attrib$vertex
> 
> where attrib$edgroup is a column that has my choice of "community" in integer 
> form, and attrib$vertex are the "names" of the vertices in the graph. if I 
> run the following,  
> 
> >> modularity(graph1,v)
> 
> then R crashes.  I also tried to clone a "communities" object, using 
> instructions from the following URL: 
> https://lists.nongnu.org/archive/html/igraph-help/2012-03/msg00075.html 
> <https://lists.nongnu.org/archive/html/igraph-help/2012-03/msg00075.html> but 
> using the typical syntax also causes R to crash:
> 
> >> modularity(graph1, membership(comms))
> 
> What's the best way to do what I'm asking?
> 
> Best,
> 
> Walter
> -- 
> 
> Walter McHugh
> Interdisciplinary M.A, Statistical Methods and Data Science
> Northeastern University
> Boston, MA
> 
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