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From ssaumitra <...@git.apache.org>
Subject [GitHub] flink pull request: [FLINK-2714] [Gelly] Copy triangle counting lo...
Date Thu, 15 Oct 2015 10:48:28 GMT
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.
    + * <p>
    + * <p>
    + * 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.
    + * <p>
    + * <p>
    + * For a group of <i>n</i> edges that share a common vertex, the number of
built triads is quadratic <i>((n*(n-1))/2)</i>.
    + * 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<K extends Comparable<K>, VV, EV> implements
GraphAlgorithm<K, VV, EV, DataSet<Tuple3<K,K,K>>> {
    +	@Override
    +	public DataSet<Tuple3<K,K,K>> run(Graph<K, VV, EV> input) throws Exception
{
    +
    +		DataSet<Edge<K, EV>> edges = input.getEdges();
    +
    +		// annotate edges with degrees
    +		DataSet<EdgeWithDegrees<K>> edgesWithDegrees = edges.flatMap(new EdgeDuplicator<K,
EV>())
    +				.groupBy(0).sortGroup(1, Order.ASCENDING).reduceGroup(new DegreeCounter<K, EV>())
    +				.groupBy(EdgeWithDegrees.V1, EdgeWithDegrees.V2).reduce(new DegreeJoiner<K>());
    +
    +		// project edges by degrees
    +		DataSet<Edge<K, NullValue>> edgesByDegree = edgesWithDegrees.map(new EdgeByDegreeProjector<K>());
    +		// project edges by vertex id
    +		DataSet<Edge<K, NullValue>> edgesById = edgesByDegree.map(new EdgeByIdProjector<K>());
    +
    +		DataSet<Tuple3<K,K,K>> 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<K>());
    +
    +		return triangles;
    +	}
    +
    +	/**
    +	 * Emits for an edge the original edge and its switched version.
    +	 */
    +	private static final class EdgeDuplicator<K, EV> implements FlatMapFunction<Edge<K,
EV>, Edge<K, EV>> {
    +
    +		@Override
    +		public void flatMap(Edge<K, EV> edge, Collector<Edge<K, EV>> out)
throws Exception {
    +			out.collect(edge);
    +			Edge<K, EV> 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<K extends Comparable<K>, EV>
    --- End diff --
    
    As I understand, you are suggesting the signature to be
    ```java
    private static final class EdgeDuplicator<K> implements FlatMapFunction<Edge<K,
EV>, Edge<K, NullValue>>
    ```
    But since this takes the raw edges passed by the caller `EV` is still necessary, right?


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