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https://issues.apache.org/jira/browse/FLINK-2570?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14711345#comment-14711345
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ASF GitHub Bot commented on FLINK-2570:
---------------------------------------
Github user vasia commented on a diff in the pull request:
https://github.com/apache/flink/pull/1054#discussion_r37869769
--- Diff:
flink-staging/flink-gelly/src/main/java/org/apache/flink/graph/library/GSATriangleCount.java
---
@@ -0,0 +1,187 @@
+/*
+ * 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.java.DataSet;
+import org.apache.flink.api.java.ExecutionEnvironment;
+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.ReduceNeighborsFunction;
+import org.apache.flink.graph.Vertex;
+import org.apache.flink.graph.Edge;
+import org.apache.flink.graph.Triplet;
+import org.apache.flink.graph.EdgeDirection;
+import org.apache.flink.graph.Graph;
+import org.apache.flink.types.NullValue;
+
+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.
+ *
+ * This implementation is non - iterative. The total number of triangles
can be determined by performing
+ * a single pass through the graph.
+ */
+public class GSATriangleCount implements
+ GraphAlgorithm<Long, NullValue, NullValue,
DataSet<Tuple1<Integer>>> {
+
+ @Override
+ public DataSet<Tuple1<Integer>> run(Graph<Long, NullValue, NullValue>
input) throws Exception {
+
+ ExecutionEnvironment env = input.getContext();
+
+ // order the edges so that src is always higher than trg
+ DataSet<Edge<Long, NullValue>> edges = input.getEdges()
+ .map(new OrderEdges()).distinct();
--- End diff --
this call to `distinct()` here means that basically if you have 2 edges
a->b and b->a in the input, and they are both part of a triangle, then you only
count it once?
> Add a Triangle Count Library Method
> -----------------------------------
>
> Key: FLINK-2570
> URL: https://issues.apache.org/jira/browse/FLINK-2570
> Project: Flink
> Issue Type: Task
> Components: Gelly
> Affects Versions: 0.10
> Reporter: Andra Lungu
> Assignee: Andra Lungu
> Priority: Minor
>
> The Gather-Sum-Apply-Scatter version of this algorithm receives an undirected
> graph as input and outputs the total number of triangles formed by the
> graph's edges.
> The implementation consists of three phases:
> 1). Select neighbours with id greater than the current vertex id.
> Gather: no-op
> Sum: create a set out of these neighbours
> Apply: attach the computed values to the vertices
> 2). Propagate each received value to neighbours with higher id (again using
> GSA)
> 3). Compute the number of Triangles by verifying if the final vertex contains
> the sender's id in its list.
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