Github user vasia commented on a diff in the pull request:
https://github.com/apache/flink/pull/1980#discussion_r63894239
--- Diff:
flink-libraries/flink-gelly/src/main/java/org/apache/flink/graph/library/similarity/JaccardIndex.java
---
@@ -0,0 +1,462 @@
+/*
+ * 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.similarity;
+
+import org.apache.flink.api.common.ExecutionConfig;
+import org.apache.flink.api.common.functions.FlatMapFunction;
+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.functions.FunctionAnnotation;
+import org.apache.flink.api.java.tuple.Tuple2;
+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.asm.degree.annotate.undirected.EdgeTargetDegree;
+import org.apache.flink.graph.library.similarity.JaccardIndex.Result;
+import org.apache.flink.graph.utils.Murmur3_32;
+import org.apache.flink.types.CopyableValue;
+import org.apache.flink.types.IntValue;
+import org.apache.flink.types.LongValue;
+import org.apache.flink.util.Collector;
+import org.apache.flink.util.Preconditions;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * The Jaccard Index measures the similarity between vertex neighborhoods.
+ * Scores range from 0.0 (no common neighbors) to 1.0 (all neighbors are
common).
+ * <br/>
+ * This implementation produces similarity scores for each pair of vertices
+ * in the graph with at least one common neighbor; equivalently, this is
the
+ * set of all non-zero Jaccard Similarity coefficients.
+ * <br/>
+ * The input graph must be a simple, undirected graph containing no
duplicate
+ * edges or self-loops.
+ *
+ * @param <K> graph ID type
+ * @param <VV> vertex value type
+ * @param <EV> edge value type
+ */
+public class JaccardIndex<K extends CopyableValue<K>, VV, EV>
+implements GraphAlgorithm<K, VV, EV, DataSet<Result<K>>> {
+
+ public static final int DEFAULT_GROUP_SIZE = 64;
+
+ // Optional configuration
+ private int groupSize = DEFAULT_GROUP_SIZE;
+
+ private boolean unboundedScores = true;
+
+ private int minimumScoreNumerator = 0;
+
+ private int minimumScoreDenominator = 1;
+
+ private int maximumScoreNumerator = 1;
+
+ private int maximumScoreDenominator = 0;
+
+ private int littleParallelism = ExecutionConfig.PARALLELISM_UNKNOWN;
+
+ /**
+ * Override the default group size for the quadratic expansion of
neighbor
+ * pairs. Small groups generate more data whereas large groups
distribute
+ * computation less evenly among tasks.
+ *
+ * @param groupSize the group size for the quadratic expansion of
neighbor pairs
+ * @return this
+ */
+ public JaccardIndex<K, VV, EV> setGroupSize(int groupSize) {
+ Preconditions.checkArgument(groupSize > 0, "Group size must be
greater than zero");
+
+ this.groupSize = groupSize;
+
+ return this;
+ }
+
+ /**
+ * Filter out Jaccard Index scores less than the given minimum fraction.
+ *
+ * @param numerator numerator of the minimum score
+ * @param denominator denominator of the minimum score
+ * @return this
+ * @see #setMaximumScore(int, int)
+ */
+ public JaccardIndex<K, VV, EV> setMinimumScore(int numerator, int
denominator) {
--- End diff --
This should be documented in the library usage docs too.
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