add layer name (_layer) to each edge

network_extensions/igraphx/multilayer.py

@@ -545,6 +545,7 @@ class MultiLayerGraph(OrderedDict):
                 logging.debug("already in: %s" % k)
                 continue
             if len(gr.vs) > 0:
+                gr.es["_layer"] = k
                 multi_layer = igraphx.union(multi_layer, gr, v_attr_name=v_attr_name, typ_field=None)
                 ##TODO  unterscheide label in different layers
                 multi_layer._components.add(k)