[ https://issues.apache.org/jira/browse/FLINK-2714?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14958723#comment-14958723 ]
ASF GitHub Bot commented on FLINK-2714:
---------------------------------------
Github user ssaumitra commented on a diff in the pull request:
https://github.com/apache/flink/pull/1250#discussion_r42108353
--- Diff: flink-libraries/flink-gelly/src/main/java/org/apache/flink/graph/library/TriangleEnumerator.java ---
@@ -0,0 +1,347 @@
+/*
+ * 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.MapFunction;
+import org.apache.flink.api.common.functions.ReduceFunction;
+import org.apache.flink.api.common.functions.FlatMapFunction;
+import org.apache.flink.api.common.functions.JoinFunction;
+import org.apache.flink.api.common.functions.GroupReduceFunction;
+import org.apache.flink.api.common.operators.Order;
+import org.apache.flink.api.java.DataSet;
+import org.apache.flink.api.java.ExecutionEnvironment;
+import org.apache.flink.api.java.functions.FunctionAnnotation;
+import org.apache.flink.api.java.tuple.Tuple3;
+import org.apache.flink.api.java.tuple.Tuple4;
+import org.apache.flink.graph.Edge;
+import org.apache.flink.graph.Graph;
+import org.apache.flink.graph.GraphAlgorithm;
+import org.apache.flink.graph.example.utils.TriangleCountData;
+import org.apache.flink.types.NullValue;
+import org.apache.flink.util.Collector;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+
+/**
+ * This function returns number of triangles present in the input graph.
+ * A triangle consists of three edges that connect three vertices with each other.
+ *
+ *

+ * The basic algorithm works as follows:
+ * It groups all edges that share a common vertex and builds triads, i.e., triples of vertices
+ * that are connected by two edges. Finally, all triads are filtered for which no third edge exists
+ * that closes the triangle.
+ *

+ *

+ * For a group of *n* edges that share a common vertex, the number of built triads is quadratic *((n*(n-1))/2)*.
+ * Therefore, an optimization of the algorithm is to group edges on the vertex with the smaller output degree to
+ * reduce the number of triads.
+ * This implementation extends the basic algorithm by computing output degrees of edge vertices and
+ * grouping on edges on the vertex with the smaller degree.
+ */
+
+public class TriangleEnumerator, VV, EV> implements GraphAlgorithm>> {
+ @Override
+ public DataSet> run(Graph input) throws Exception {
+
+ DataSet> edges = input.getEdges();
+
+ // annotate edges with degrees
+ DataSet> edgesWithDegrees = edges.flatMap(new EdgeDuplicator())
+ .groupBy(0).sortGroup(1, Order.ASCENDING).reduceGroup(new DegreeCounter())
+ .groupBy(EdgeWithDegrees.V1, EdgeWithDegrees.V2).reduce(new DegreeJoiner());
+
+ // project edges by degrees
+ DataSet> edgesByDegree = edgesWithDegrees.map(new EdgeByDegreeProjector());
+ // project edges by vertex id
+ DataSet> edgesById = edgesByDegree.map(new EdgeByIdProjector());
+
+ DataSet> triangles = edgesByDegree
+ // build triads
+ .groupBy(EdgeWithDegrees.V1).sortGroup(EdgeWithDegrees.V2, Order.ASCENDING)
+ .reduceGroup(new TriadBuilder())
+ // filter triads
+ .join(edgesById).where(Triad.V2, Triad.V3).equalTo(0, 1).with(new TriadFilter());
+
+ return triangles;
+ }
+
+ /**
+ * Emits for an edge the original edge and its switched version.
+ */
+ private static final class EdgeDuplicator implements FlatMapFunction, Edge> {
+
+ @Override
+ public void flatMap(Edge edge, Collector> out) throws Exception {
+ out.collect(edge);
+ Edge reversed = edge.reverse();
+ out.collect(reversed);
+ }
+ }
+
+ /**
+ * Counts the number of edges that share a common vertex.
+ * Emits one edge for each input edge with a degree annotation for the shared vertex.
+ * For each emitted edge, the first vertex is the vertex with the smaller id.
+ */
+ private static final class DegreeCounter, EV>
--- End diff --
As I understand, you are suggesting the signature to be
```java
private static final class EdgeDuplicator implements FlatMapFunction, Edge>
```
But since this takes the raw edges passed by the caller `EV` is still necessary, right?
> Port the Flink DataSet Triangle Enumeration example to the Gelly library
> ------------------------------------------------------------------------
>
> Key: FLINK-2714
> URL: https://issues.apache.org/jira/browse/FLINK-2714
> Project: Flink
> Issue Type: Task
> Components: Gelly
> Affects Versions: 0.10
> Environment:
> Reporter: Andra Lungu
> Assignee: Saumitra Shahapure
> Priority: Trivial
> Labels: newbie, starter
>
> Currently, the Gelly library contains one method for counting the number of triangles in a graph: a gather-apply-scatter version.
> This issue proposes the addition of a library method based on this Flink example:
> https://github.com/apache/flink/blob/master/flink-examples/flink-java-examples/src/main/java/org/apache/flink/examples/java/graph/EnumTrianglesOpt.java
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