It did not do that. I anyway have a workaround for that. There's another issue I am encountering. Before doing a union of two graphs (g1, g2), I filter out 5 vertices in g1 which actually has 20 nodes, leaving it with 15 vertices. The num_vertices() function returns the value 15 but the last node still has an index of 19. So after union, in the vertex list the graph g2 gets appended to the end of g1, which I assumed to be starting at index 15, but its at 20. I understand that the filter is reversible, but is there any way to re-arrange indices after a filtering operation so that there is a consistency with the vertex index and the number of vertices actually being considered now? Thanks, Kavya -- View this message in context: http://main-discussion-list-for-the-graph-tool-project.982480.n3.nabble.com/... Sent from the Main discussion list for the graph-tool project mailing list archive at Nabble.com.