Using an edge_property on GraphView

graph-tool
#1

Is it correct to use an edge property map of a graph with a graph view based
on that graph? Specifically, I have an edge property of edge weights. I then
filter the graph to the largest connected component, and then I want to run
nested blockmodel on that largest connected component with the corresponding
edge weights.

The exact code I want to use is below. Is this correct, or do I need to also
filter weight_prop so that it only has information about edges not filtered
in the GraphView GL?

Thank you so much!

  EDGES, WEIGHT_V = get_edge_set(ADJ, WEIGHTS, N, K)
  G = gt.Graph()
  G.add_vertex(N)
  G.add_edge_list(EDGES)
  G.set_directed(False)
  largest = graph_tool.topology.label_largest_component(G)
  GL = gt.GraphView(G, vfilt=largest)
  weight_prop = G.new_edge_property("int16_t")
  weight_prop.a = WEIGHT_V
  NBM = graph_tool.community.minimize_nested_blockmodel_dl(GL, verbose=True,
epsilon=E, eweight=weight_prop)

#2

This will work in many cases, but is not a good idea, since the property
map created with the original graph has no information on the
filtering. This is often not an issue, since the edge and vertex indexes
are the same in both graphs, and thus the property mapping works as
expected. But some algorithms expect the length of the array returned by
the ".fa" attribute to match the number of vertices / edges which are
not filtered.

In the example above, you could have done simply

   weight_prop = GL.new_edge_property("int16_t")

to avoid any problems.

Best,
Tiago