Faster Graph::transpose

networkit/cpp/graph/Graph.cpp

@@ -11,7 +11,6 @@
 #include <sstream>
 
 #include <networkit/graph/Graph.hpp>
-#include <networkit/graph/GraphBuilder.hpp>
 
 namespace NetworKit {
 
@@ -1071,21 +1070,45 @@ std::vector<node> Graph::neighbors(node u) const {
 Graph Graph::transpose() const {
 	if (directed == false) {
 		throw std::runtime_error("The transpose of an undirected graph is "
-		                         "identical to the original graph.");
+								 "identical to the original graph.");
 	}
 
-	GraphBuilder gB(z, weighted, true);
+	Graph GTranspose(z, weighted, true);
 
-	this->forEdges([&](node u, node v) { gB.addHalfEdge(v, u, weight(u, v)); });
+	// prepare edge id storage if input has indexed edges
+	GTranspose.edgesIndexed = edgesIndexed;
+	GTranspose.omega = omega;
+	if (edgesIndexed) {
+		GTranspose.inEdgeIds.resize(z);
+		GTranspose.outEdgeIds.resize(z);
+	}
 
-	Graph GTranspose = gB.toGraph(true);
-	for (node u = 0; u < z; ++u) {
-		if (!exists[u]) {
+	#pragma omp parallel for
+	for (omp_index u = 0; u <  static_cast<omp_index>(z); ++u) {
+		if (exists[u]) {
+			GTranspose.preallocateDirected(u, degreeIn(u), degreeOut(u));
+
+			forInEdgesOf(u, [&] (node, node v, edgeweight w, edgeid id) {
+				GTranspose.addPartialOutEdge(unsafe, u, v, w, id);
+			});
+
+			forEdgesOf(u, [&] (node, node v, edgeweight w, edgeid id) {
+				GTranspose.addPartialInEdge(unsafe, u, v, w, id);
+			});
+
+		} else {
+			#pragma omp critical
 			GTranspose.removeNode(u);
 		}
 	}
+
+	GTranspose.setEdgeCount(unsafe, numberOfEdges());
+	GTranspose.setNumberOfSelfLoops(unsafe, numberOfSelfLoops());
 	GTranspose.t = t;
 	GTranspose.setName(getName() + "Transpose");
+
+	assert(GTranspose.checkConsistency());
+
 	return GTranspose;
 }
 

networkit/test/test_graph.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 import unittest
+import random
 import networkit as nk
 
 class TestGraph(unittest.TestCase):
@@ -13,8 +14,7 @@ def getSmallGraph(self, weighted=False, directed=False):
 
 		return G
 
-	def testSubgraphFromNodes(self):
-		# Directed
+	def testSubgraphFromNodesDirected(self):
 		G = self.getSmallGraph(True, True)
 
 		res = G.subgraphFromNodes([0])
@@ -39,8 +39,8 @@ def testSubgraphFromNodes(self):
 		self.assertEqual(res.numberOfNodes(), 4)
 		self.assertEqual(res.numberOfEdges(), 4)
 
-		# Undirected
-		G = G.toUndirected()
+	def testSubgraphFromNodesUndirected(self):
+		G = self.getSmallGraph(True, False)
 
 		res = G.subgraphFromNodes([0])
 		self.assertTrue(res.isWeighted())
@@ -121,5 +121,47 @@ def testNeighbors(self):
 		self.assertEqual(sorted(G.neighbors(2)), [0, 1, 3])
 		self.assertEqual(sorted(G.neighbors(3)), [1, 2])
 
+	def testGraphTranspose(self):
+		nk.setSeed(1, True)
+		G = nk.generators.ErdosRenyiGenerator(100, 0.2, True).generate()
+
+		for i in range(20):
+			u = G.randomNode()
+			if not G.hasEdge(u, u):
+				G.addEdge(u, u)
+		self.assertGreater(G.numberOfSelfLoops(), 0)
+
+		# Delete a few nodes
+		for i in range(10):
+			G.removeNode(G.randomNode())
+		self.assertGreater(G.numberOfSelfLoops(), 0)
+
+		# Assign random weights
+		GWeighted = nk.Graph(G, True, True)
+		for u, v in GWeighted.edges():
+			GWeighted.setWeight(u, v, random.random())
+
+		GWeighted.indexEdges()
+
+		GTrans = GWeighted.transpose()
+
+		for u, v in GWeighted.edges():
+			self.assertEqual(GWeighted.edgeId(u, v), GTrans.edgeId(v, u))
+			self.assertEqual(GWeighted.weight(u, v), GTrans.weight(v, u))
+
+		for v, u in GTrans.edges():
+			self.assertEqual(GWeighted.edgeId(u, v), GTrans.edgeId(v, u))
+			self.assertEqual(GWeighted.weight(u, v), GTrans.weight(v, u))
+
+		for u in range(GWeighted.upperNodeIdBound()):
+			self.assertEqual(GWeighted.hasNode(u), GTrans.hasNode(u))
+
+		self.assertEqual(GWeighted.upperEdgeIdBound(),  GTrans.upperEdgeIdBound())
+		self.assertEqual(GWeighted.upperNodeIdBound(),  GTrans.upperNodeIdBound())
+		self.assertEqual(GWeighted.numberOfSelfLoops(), GTrans.numberOfSelfLoops())
+		self.assertEqual(GWeighted.numberOfNodes(),     GTrans.numberOfNodes())
+		self.assertEqual(GWeighted.numberOfEdges(),     GTrans.numberOfEdges())
+
+
 if __name__ == "__main__":
 	unittest.main()