[igraph] Collapsing/Folding graph based on vertex attributes

[S. M. Ali Abbas]

Hi folks,
I have got a graph with this detail:

> summary(g)
IGRAPH UN-- 7690383 7839216 --
attr: Ethnic.Group(v/c), Geographical.Area (v/c), Religion (v/c), Major.Language (v/c)

I'd like to collapse/reduce my graph to a new graph, where the vertices are grouped together according to their Ethnic.Group attribute, for instance, and then visualize the edges between them. As an example, all vertices with a certain ethnicity, X, should be grouped together (the size of the new vertex should correspond to the number of vertices with X as their ethnicity), and the edge would also be weighted (the number of links between ethnicity X and Y).
For visualization of the whole graph, I used Gephi which supports grouping of vertices, but unfortunately my system can't handle such a big graph - of 1G size. I'd like to reduce the graph using igraph, and then export it to Gephi for visualization.

Thanks!

Cheers,
Ali