Merge 293fd05 into 61f41d4

networkx/algorithms/components/strongly_connected.py

@@ -311,7 +311,9 @@ def condensation(G, scc=None):
     C : NetworkX DiGraph
        The condensation of G. The node labels are integers corresponding
        to the index of the component in the list of strongly connected
-       components.
+       components. It has a graph attribute named 'mapping' with a
+       dictionary mapping the original nodes to the nodes in the
+       condensation graph (ie SCC) to which they belong.
 
     Raises
     ------
@@ -334,4 +336,6 @@ def condensation(G, scc=None):
     for u,v in G.edges():
         if mapping[u] != mapping[v]:
             C.add_edge(mapping[u],mapping[v])
+    # Add mapping dict as graph attribute
+    C.graph['mapping'] = mapping
     return C

networkx/algorithms/components/tests/test_strongly_connected.py

@@ -128,6 +128,14 @@ def test_contract_scc_edge(self):
             edge = (1,0)
         assert_equal(cG.edges(),[edge])
 
+    def test_condensation_mapping(self):
+        G, C = self.gc[1]
+        cG = nx.condensation(G)
+        mapping = cG.graph['mapping']
+        assert_true(all(n in G for n in mapping))
+        assert_true(all(0 == cN for n, cN in mapping.items() if n in C[0]))
+        assert_true(all(1 == cN for n, cN in mapping.items() if n in C[1]))
+
     def test_connected_raise(self):
         G=nx.Graph()
         assert_raises(NetworkXNotImplemented,nx.strongly_connected_components,G)