[WIP] Degree Centrality (#830)

* uncomment test

* For Cypher loading we will always treat the graph as outgoing, and let the user handle the actual direction in the query

* deduplicate nodes in Cypher loading land

* deduplicate nodes in Graph View land

* tests for new custom counting

* degree centrality proc

* Integration test

* Integration test for weighted

* tests for outgoing

* use the proper threading approach

* use the proper threading approach for weighted

* Partition Degree Centrality computation

* weighted degree in the same class

* remove unused code

* put the direction logic into the loader

* handle Cypher loading

* use the sum strategy for accumulating weight degrees

* use the correct duplicates strategy in these tests

algo/src/main/java/org/neo4j/graphalgo/DegreeCentralityProc.java

@@ -0,0 +1,230 @@
+/**
+ * Copyright (c) 2017 "Neo4j, Inc." <http://neo4j.com>
+ *
+ * This file is part of Neo4j Graph Algorithms <http://github.com/neo4j-contrib/neo4j-graph-algorithms>.
+ *
+ * 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.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.neo4j.graphalgo;
+
+import org.neo4j.graphalgo.api.Graph;
+import org.neo4j.graphalgo.api.GraphFactory;
+import org.neo4j.graphalgo.api.HugeGraph;
+import org.neo4j.graphalgo.core.GraphLoader;
+import org.neo4j.graphalgo.core.ProcedureConfiguration;
+import org.neo4j.graphalgo.core.ProcedureConstants;
+import org.neo4j.graphalgo.core.utils.Pools;
+import org.neo4j.graphalgo.core.utils.ProgressTimer;
+import org.neo4j.graphalgo.core.utils.TerminationFlag;
+import org.neo4j.graphalgo.core.utils.paged.AllocationTracker;
+import org.neo4j.graphalgo.core.write.Exporter;
+import org.neo4j.graphalgo.impl.Algorithm;
+import org.neo4j.graphalgo.impl.degree.DegreeCentrality;
+import org.neo4j.graphalgo.impl.results.CentralityResult;
+import org.neo4j.graphalgo.impl.pagerank.DegreeCentralityAlgorithm;
+import org.neo4j.graphalgo.results.DegreeCentralityScore;
+import org.neo4j.graphdb.Direction;
+import org.neo4j.kernel.api.KernelTransaction;
+import org.neo4j.kernel.internal.GraphDatabaseAPI;
+import org.neo4j.logging.Log;
+import org.neo4j.procedure.*;
+
+import java.util.Map;
+import java.util.stream.IntStream;
+import java.util.stream.LongStream;
+import java.util.stream.Stream;
+
+import static org.neo4j.graphalgo.core.ProcedureConstants.CYPHER_QUERY;
+
+public final class DegreeCentralityProc {
+
+    public static final String DEFAULT_SCORE_PROPERTY = "degree";
+    public static final String CONFIG_WEIGHT_KEY = "weightProperty";
+
+    @Context
+    public GraphDatabaseAPI api;
+
+    @Context
+    public Log log;
+
+    @Context
+    public KernelTransaction transaction;
+
+    @Procedure(value = "algo.degree", mode = Mode.WRITE)
+    @Description("CALL algo.degree(label:String, relationship:String, " +
+            "{ weightProperty: null, write: true, writeProperty:'degree', concurrency:4}) " +
+            "YIELD nodes, iterations, loadMillis, computeMillis, writeMillis, dampingFactor, write, writeProperty" +
+            " - calculates page rank and potentially writes back")
+    public Stream<DegreeCentralityScore.Stats> degree(
+            @Name(value = "label", defaultValue = "") String label,
+            @Name(value = "relationship", defaultValue = "") String relationship,
+            @Name(value = "config", defaultValue = "{}") Map<String, Object> config) {
+
+        ProcedureConfiguration configuration = ProcedureConfiguration.create(config);
+        final String weightPropertyKey = configuration.getString(CONFIG_WEIGHT_KEY, null);
+
+        DegreeCentralityScore.Stats.Builder statsBuilder = new DegreeCentralityScore.Stats.Builder();
+        AllocationTracker tracker = AllocationTracker.create();
+        Direction direction = getDirection(configuration);
+        final Graph graph = load(label, relationship, tracker, configuration.getGraphImpl(), statsBuilder, configuration, weightPropertyKey, direction);
+
+        if(graph.nodeCount() == 0) {
+            graph.release();
+            return Stream.of(statsBuilder.build());
+        }
+
+        TerminationFlag terminationFlag = TerminationFlag.wrap(transaction);
+        CentralityResult scores = evaluate(graph, tracker, terminationFlag, configuration, statsBuilder, weightPropertyKey, direction);
+
+        logMemoryUsage(tracker);
+
+        write(graph, terminationFlag, scores, configuration, statsBuilder);
+
+        return Stream.of(statsBuilder.build());
+    }
+
+    private Direction getDirection(ProcedureConfiguration configuration) {
+        String graphName = configuration.getGraphName(ProcedureConstants.DEFAULT_GRAPH_IMPL);
+        Direction direction = configuration.getDirection(Direction.INCOMING);
+        return CYPHER_QUERY.equals(graphName) ? Direction.OUTGOING : direction;
+    }
+
+    @Procedure(value = "algo.degree.stream", mode = Mode.READ)
+    @Description("CALL algo.degree.stream(label:String, relationship:String, " +
+            "{weightProperty: null, concurrency:4}) " +
+            "YIELD node, score - calculates page rank and streams results")
+    public Stream<DegreeCentralityScore> degreeStream(
+            @Name(value = "label", defaultValue = "") String label,
+            @Name(value = "relationship", defaultValue = "") String relationship,
+            @Name(value = "config", defaultValue = "{}") Map<String, Object> config) {
+
+            ProcedureConfiguration configuration = ProcedureConfiguration.create(config);
+
+        final String weightPropertyKey = configuration.getString(CONFIG_WEIGHT_KEY, null);
+
+        DegreeCentralityScore.Stats.Builder statsBuilder = new DegreeCentralityScore.Stats.Builder();
+        Direction direction = getDirection(configuration);
+        AllocationTracker tracker = AllocationTracker.create();
+        final Graph graph = load(label, relationship, tracker, configuration.getGraphImpl(), statsBuilder, configuration, weightPropertyKey, direction);
+
+        if(graph.nodeCount() == 0) {
+            graph.release();
+            return Stream.empty();
+        }
+
+        TerminationFlag terminationFlag = TerminationFlag.wrap(transaction);
+        CentralityResult scores = evaluate(graph, tracker, terminationFlag, configuration, statsBuilder, weightPropertyKey, direction);
+
+        logMemoryUsage(tracker);
+
+        if (graph instanceof HugeGraph) {
+            HugeGraph hugeGraph = (HugeGraph) graph;
+            return LongStream.range(0, hugeGraph.nodeCount())
+                    .mapToObj(i -> {
+                        final long nodeId = hugeGraph.toOriginalNodeId(i);
+                        return new DegreeCentralityScore(
+                                nodeId,
+                                scores.score(i)
+                        );
+                    });
+        }
+
+        return IntStream.range(0, Math.toIntExact(graph.nodeCount()))
+                .mapToObj(i -> {
+                    final long nodeId = graph.toOriginalNodeId(i);
+                    return new DegreeCentralityScore(
+                            nodeId,
+                            scores.score(i)
+                    );
+                });
+    }
+
+    private void logMemoryUsage(AllocationTracker tracker) {
+        log.info("Degree Centrality: overall memory usage: %s", tracker.getUsageString());
+    }
+
+    private Graph load(
+            String label,
+            String relationship,
+            AllocationTracker tracker,
+            Class<? extends GraphFactory> graphFactory,
+            DegreeCentralityScore.Stats.Builder statsBuilder,
+            ProcedureConfiguration configuration,
+            String weightPropertyKey, Direction direction) {
+        GraphLoader graphLoader = new GraphLoader(api, Pools.DEFAULT)
+                .init(log, label, relationship, configuration)
+                .withAllocationTracker(tracker)
+                .withOptionalRelationshipWeightsFromProperty(weightPropertyKey, configuration.getWeightPropertyDefaultValue(0.0));
+
+        graphLoader.direction(direction);
+
+        try (ProgressTimer timer = statsBuilder.timeLoad()) {
+            Graph graph = graphLoader.load(graphFactory);
+            statsBuilder.withNodes(graph.nodeCount());
+            return graph;
+        }
+    }
+
+    private CentralityResult evaluate(
+            Graph graph,
+            AllocationTracker tracker,
+            TerminationFlag terminationFlag,
+            ProcedureConfiguration configuration,
+            DegreeCentralityScore.Stats.Builder statsBuilder,
+            String weightPropertyKey, Direction direction) {
+
+        final int concurrency = configuration.getConcurrency(Pools.getNoThreadsInDefaultPool());
+
+        if (direction == Direction.BOTH) {
+            direction = Direction.OUTGOING;
+        }
+
+        DegreeCentralityAlgorithm algo = new DegreeCentrality(graph, Pools.DEFAULT, concurrency, direction, weightPropertyKey != null);
+        statsBuilder.timeEval(algo::compute);
+        Algorithm<?> algorithm = algo.algorithm();
+        algorithm.withTerminationFlag(terminationFlag);
+
+        final CentralityResult pageRank = algo.result();
+        algo.algorithm().release();
+        graph.release();
+        return pageRank;
+    }
+
+    private void write(
+            Graph graph,
+            TerminationFlag terminationFlag,
+            CentralityResult result,
+            ProcedureConfiguration configuration,
+            final DegreeCentralityScore.Stats.Builder statsBuilder) {
+        if (configuration.isWriteFlag(true)) {
+            log.debug("Writing results");
+            String propertyName = configuration.getWriteProperty(DEFAULT_SCORE_PROPERTY);
+            try (ProgressTimer timer = statsBuilder.timeWrite()) {
+                Exporter exporter = Exporter
+                        .of(api, graph)
+                        .withLog(log)
+                        .parallel(Pools.DEFAULT, configuration.getConcurrency(), terminationFlag)
+                        .build();
+                result.export(propertyName, exporter);
+            }
+            statsBuilder
+                    .withWrite(true)
+                    .withProperty(propertyName);
+        } else {
+            statsBuilder.withWrite(false);
+        }
+    }
+
+
+}