overlap function

Author: Mark Needham

algo/src/main/java/org/neo4j/graphalgo/similarity/Similarities.java

@@ -1,18 +1,18 @@
 /**
  * Copyright (c) 2017 "Neo4j, Inc." <http://neo4j.com>
- *
+ * <p>
  * This file is part of Neo4j Graph Algorithms <http://github.com/neo4j-contrib/neo4j-graph-algorithms>.
- *
+ * <p>
  * Neo4j Graph Algorithms is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation, either version 3 of the License, or
  * (at your option) any later version.
- *
+ * <p>
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
- *
+ * <p>
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
@@ -38,7 +38,7 @@ public double jaccardSimilarity(@Name("vector1") List<Number> vector1, @Name("ve
         int intersection = intersectionSet.size();
 
         long denominator = vector1.size() + vector2.size() - intersection;
-        return denominator == 0 ? 0 : (double)intersection / denominator;
+        return denominator == 0 ? 0 : (double) intersection / denominator;
     }
 
     @UserFunction("algo.similarity.cosine")
@@ -92,4 +92,18 @@ public double euclideanDistance(@Name("vector1") List<Number> vector1, @Name("ve
     public double euclideanSimilarity(@Name("vector1") List<Number> vector1, @Name("vector2") List<Number> vector2) {
         return 1.0d / (1 + euclideanDistance(vector1, vector2));
     }
-}
+
+    @UserFunction("algo.similarity.overlap")
+    @Description("algo.similarity.overlap([vector1], [vector2]) " +
+            "given two collection vectors, calculate overlap similarity")
+    public double overlapSimilarity(@Name("vector1") List<Number> vector1, @Name("vector2") List<Number> vector2) {
+        if (vector1 == null || vector2 == null) return 0;
+
+        HashSet<Number> intersectionSet = new HashSet<>(vector1);
+        intersectionSet.retainAll(vector2);
+        int intersection = intersectionSet.size();
+
+        long denominator = Math.min(vector1.size(), vector2.size());
+        return denominator == 0 ? 0 : (double) intersection / denominator;
+    }
+}

tests/src/test/java/org/neo4j/graphalgo/algo/similarity/SimilaritiesTest.java

@@ -188,6 +188,33 @@ public void testJaccardSimilarity() throws Exception {
         assertEquals(bobSim, result.next().get("jaccardSim"));
         assertEquals(jimSim, result.next().get("jaccardSim"));
     }
+    
+    @Test
+    public void testOverlapSimilarity() throws Exception {
+        String controlQuery =
+                "MATCH (p1:Employee)-[:HAS_SKILL]->(sk)<-[:HAS_SKILL]-(p2)\n" +
+                        "WITH p1,p2,size((p1)-[:HAS_SKILL]->()) as d1, size((p2)-[:HAS_SKILL]->()) as d2, count(distinct sk) as intersection\n" +
+                        "WITH p1.name as name1, p2.name as name2, toFloat(intersection) / CASE WHEN d1 > d2 THEN d2 ELSE d1 END as overlapSim\n" +
+                        "ORDER BY name1,name2\n" +
+                        "RETURN name1,name2, toString(toInteger(overlapSim*10000)/10000.0) as overlapSim";
+        String bobSim;
+        String jimSim;
+        try (Transaction tx = db.beginTx()) {
+            Result result = db.execute(controlQuery);
+            bobSim = (String) result.next().get("overlapSim");
+            jimSim = (String) result.next().get("overlapSim");
+        }
+
+        Result result = db.execute(
+                "MATCH (p1:Employee),(p2:Employee) WHERE p1 <> p2\n" +
+                        "WITH p1, [(p1)-[:HAS_SKILL]->(sk) | id(sk)] as v1, p2, [(p2)-[:HAS_SKILL]->(sk) | id(sk)] as v2\n" +
+                        "WITH p1.name as name1, p2.name as name2, algo.similarity.overlap(v1, v2) as overlapSim ORDER BY name1,name2\n" +
+                        "RETURN name1, name2, toString(toInteger(overlapSim*10000)/10000.0) as overlapSim");
+
+        assertEquals(bobSim, result.next().get("overlapSim"));
+        assertEquals(jimSim, result.next().get("overlapSim"));
+    }
+
     @Test
     public void testEuclideanSimilarity() throws Exception {
         String controlQuery =
@@ -217,4 +244,4 @@ public void testEuclideanSimilarity() throws Exception {
         assertEquals(bobSim, result.next().get("euclidSim"));
         assertEquals(jimSim, result.next().get("euclidSim"));
     }
-}
+}