Github user vasia commented on a diff in the pull request:
https://github.com/apache/flink/pull/1105#discussion_r39928365
--- Diff:
flink-staging/flink-gelly/src/main/java/org/apache/flink/graph/library/TriangleCount.java
---
@@ -0,0 +1,208 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.graph.library;
+
+import org.apache.flink.api.common.functions.FlatJoinFunction;
+import org.apache.flink.api.common.functions.GroupReduceFunction;
+import org.apache.flink.api.common.functions.MapFunction;
+import org.apache.flink.api.common.functions.ReduceFunction;
+import org.apache.flink.api.java.DataSet;
+import org.apache.flink.api.java.tuple.Tuple1;
+import org.apache.flink.api.java.tuple.Tuple2;
+import org.apache.flink.graph.GraphAlgorithm;
+import org.apache.flink.graph.Graph;
+import org.apache.flink.graph.Vertex;
+import org.apache.flink.graph.Edge;
+import org.apache.flink.graph.EdgeDirection;
+import org.apache.flink.graph.NeighborsFunctionWithVertexValue;
+import org.apache.flink.graph.utils.VertexToTuple2Map;
+import org.apache.flink.types.NullValue;
+import org.apache.flink.util.Collector;
+
+import java.util.Iterator;
+import java.util.TreeMap;
+
+/**
+ * Triangle Count Algorithm.
+ *
+ * This algorithm operates in three phases. First, vertices select
neighbors with id greater than theirs
+ * and send messages to them. Each received message is then propagated to
neighbors with higher id.
+ * Finally, if a node encounters the target id in the list of received
messages, it increments the number
+ * of triangles found.
+ *
+ * For skewed graphs, we recommend calling the GSATriangleCount library
method as it uses the more restrictive
+ * `reduceOnNeighbors` function which internally makes use of combiners to
speed up computation.
+ *
+ * This implementation is non - iterative.
+ *
+ * The algorithm takes an undirected, unweighted graph as input and
outputs a DataSet of
+ * Tuple1 which contains a single integer representing the number of
triangles.
+ */
+public class TriangleCount implements
+ GraphAlgorithm<Long, NullValue, NullValue,
DataSet<Tuple1<Integer>>> {
+
+ @Override
+ public DataSet<Tuple1<Integer>> run(Graph<Long, NullValue, NullValue>
graph) throws Exception {
+
+ // simulate the first superstep
+ // select the neighbors with id greater than the current
vertex's id
+ DataSet<Vertex<Long, Long>> verticesWithHigherNeighbors =
+ graph.groupReduceOnNeighbors(new
GatherHigherIdNeighbors(), EdgeDirection.IN);
+
+ // then group them by id to attach the resulting sets to the
vertices
+ DataSet<Vertex<Long, TreeMap<Long, Integer>>>
verticesWithNeighborTreeMaps =
+
verticesWithHigherNeighbors.groupBy(0).reduceGroup(new
AttachNeighborIdsAsVertexValues());
+
+ // assign a value to the vertices with no neighbors as well
+ Graph<Long, TreeMap<Long, Integer>, NullValue>
graphWithInitializedVertexNeighbors =
+ graph.mapVertices(new InitializeTreeMaps());
+
+ Graph<Long, TreeMap<Long, Integer>, NullValue>
graphWithVertexNeighbors = graphWithInitializedVertexNeighbors.
+
joinWithVertices(verticesWithNeighborTreeMaps.map(new VertexToTuple2Map<Long,
TreeMap<Long, Integer>>()),
+ new RetrieveValueMapper());
+
+ // simulate the second superstep
+ // propagate each received "message" to neighbors with higher id
+ DataSet<Vertex<Long, Long>> verticesWithPropagatedValues =
+
graphWithVertexNeighbors.groupReduceOnNeighbors(new PropagateNeighborValues(),
EdgeDirection.IN);
+
+ DataSet<Vertex<Long, TreeMap<Long, Integer>>>
verticesWithPropagatedTreeMaps =
+
verticesWithPropagatedValues.groupBy(0).reduceGroup(new
AttachNeighborIdsAsVertexValues());
+
+ DataSet<Tuple1<Integer>> numberOfTriangles =
verticesWithPropagatedTreeMaps
+ .join(graph.getEdges())
+ .where(0).equalTo(0).with(new
CountTriangles()).reduce(new ReduceFunction<Tuple1<Integer>>() {
+
+ @Override
+ public Tuple1<Integer>
reduce(Tuple1<Integer> firstTuple, Tuple1<Integer> secondTuple) throws
Exception {
+ return new
Tuple1<Integer>(firstTuple.f0 + secondTuple.f0);
+ }
+ });
+
+ return numberOfTriangles;
+ }
+
+ @SuppressWarnings("serial")
+ private static final class GatherHigherIdNeighbors implements
+ NeighborsFunctionWithVertexValue<Long, NullValue,
NullValue, Vertex<Long, Long>> {
+
+ @Override
+ public void iterateNeighbors(Vertex<Long, NullValue> vertex,
+
Iterable<Tuple2<Edge<Long, NullValue>, Vertex<Long, NullValue>>> neighbors,
+ Collector<Vertex<Long,
Long>> collector) throws Exception {
+
+ Tuple2<Edge<Long, NullValue>, Vertex<Long, NullValue>>
next = null;
+ Iterator<Tuple2<Edge<Long, NullValue>, Vertex<Long,
NullValue>>> neighborsIterator =
+ neighbors.iterator();
+
+ while (neighborsIterator.hasNext()) {
+ next = neighborsIterator.next();
+ if(next.f1.getId() > vertex.getId()) {
+ collector.collect(new Vertex<Long,
Long>(next.f1.getId(), vertex.getId()));
+ }
+ }
+ }
+ }
+
+ @SuppressWarnings("serial")
+ private static final class AttachNeighborIdsAsVertexValues implements
GroupReduceFunction<Vertex<Long, Long>,
+ Vertex<Long, TreeMap<Long, Integer>>> {
+
+ @Override
+ public void reduce(Iterable<Vertex<Long, Long>> vertices,
+ Collector<Vertex<Long, TreeMap<Long,
Integer>>> collector) throws Exception {
+
+ Iterator<Vertex<Long, Long>> vertexIertator =
vertices.iterator();
+ Vertex<Long, Long> next = null;
+ TreeMap<Long, Integer> neighbors = new TreeMap<Long,
Integer>();
+ Long id = null;
+
+ while (vertexIertator.hasNext()) {
+ next = vertexIertator.next();
+ id = next.getId();
+
+ Integer value = neighbors.get(next.getValue());
+ if (value != null) {
+ neighbors.put(next.getValue(), value +
1);
+ } else {
+ neighbors.put(next.getValue(), 1);
+ }
+ }
+
+ collector.collect(new Vertex<Long, TreeMap<Long,
Integer>>(id, neighbors));
+ }
+ }
+
+ @SuppressWarnings("serial")
+ private static final class InitializeTreeMaps implements
MapFunction<Vertex<Long, NullValue>, TreeMap<Long, Integer>> {
+
+ @Override
+ public TreeMap<Long, Integer> map(Vertex<Long, NullValue>
vertex) throws Exception {
+ return new TreeMap<Long, Integer>();
+ }
+ }
+
+ @SuppressWarnings("serial")
+ private static final class RetrieveValueMapper implements
MapFunction<Tuple2<TreeMap<Long, Integer>,
+ TreeMap<Long, Integer>>, TreeMap<Long, Integer>> {
+
+ @Override
+ public TreeMap<Long, Integer> map(Tuple2<TreeMap<Long,
Integer>, TreeMap<Long, Integer>> value) throws Exception {
+ return value.f1;
--- End diff --
I believe you can simplify this with a `project(1)`.
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