[graph-tool] Re: Creating a layered graph (aka messing with property maps)

I may have found a way to go, but I'd like to know what I was doing wrong before. Now I don't create a new graph by union, but this (as vertex numbers and indexes are the same): gu = gt.Graph(directed=False) gu.add_vertex(g_atac.num_vertices()) layer = gu.new_edge_property('int') for e in g_rna.edges(): ne = gu.add_edge(e.source(), e.target()) layer[ne] = -1 for e in g_atac.edges(): ne = gu.add_edge(e.source(), e.target()) layer[ne] = 1 gu.ep['layer'] = layer this works and the final graph has 2 layers and no extra zeros