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From fhueske <...@git.apache.org>
Subject [GitHub] flink pull request: [FLINK-2634] [gelly] Added a vertex-centric Tr...
Date Fri, 11 Sep 2015 14:42:44 GMT
Github user fhueske commented on a diff in the pull request:

    --- 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
    + * Tuple1 which contains a single integer representing the number of triangles.
    + */
    +public class TriangleCount implements
    +		GraphAlgorithm<Long, NullValue, NullValue, DataSet<Tuple1<Integer>>>
    --- End diff --
    The key must implement the `org.apache.flink.types.Key` interface. Otherwise, you could
not group, join, sort on this type. `Key` implements `Comparable`, so you can simply do `key1.compareTo(key2)`.

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