gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/ranking/pagerank/PageRankMapReduce.java

/*
 * 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.tinkerpop.gremlin.process.computer.ranking.pagerank;

import org.apache.tinkerpop.gremlin.process.computer.KeyValue;
import org.apache.tinkerpop.gremlin.process.computer.util.StaticMapReduce;
import org.apache.tinkerpop.gremlin.structure.Graph;
import org.apache.tinkerpop.gremlin.structure.Property;
import org.apache.tinkerpop.gremlin.structure.Vertex;
import org.apache.tinkerpop.gremlin.structure.util.StringFactory;
import org.apache.commons.configuration2.Configuration;

import java.util.Iterator;

/**
 * @author Marko A. Rodriguez (http://markorodriguez.com)
 */
public class PageRankMapReduce extends StaticMapReduce<Object, Double, Object, Double, Iterator<KeyValue<Object, Double>>> {

    public static final String PAGE_RANK_MEMORY_KEY = "gremlin.pageRankMapReduce.memoryKey";
    public static final String DEFAULT_MEMORY_KEY = "pageRank";

    private String memoryKey = DEFAULT_MEMORY_KEY;

    private PageRankMapReduce() {

    }

    private PageRankMapReduce(final String memoryKey) {
        this.memoryKey = memoryKey;
    }

    @Override
    public void storeState(final Configuration configuration) {
        super.storeState(configuration);
        configuration.setProperty(PAGE_RANK_MEMORY_KEY, this.memoryKey);
    }

    @Override
    public void loadState(final Graph graph, final Configuration configuration) {
        this.memoryKey = configuration.getString(PAGE_RANK_MEMORY_KEY, DEFAULT_MEMORY_KEY);
    }

    @Override
    public boolean doStage(final Stage stage) {
        return stage.equals(Stage.MAP);
    }

    @Override
    public void map(final Vertex vertex, final MapEmitter<Object, Double> emitter) {
        final Property pageRank = vertex.property(PageRankVertexProgram.PAGE_RANK);
        if (pageRank.isPresent()) {
            emitter.emit(vertex.id(), (Double) pageRank.value());
        }
    }

    @Override
    public Iterator<KeyValue<Object, Double>> generateFinalResult(final Iterator<KeyValue<Object, Double>> keyValues) {
        return keyValues;
    }

    @Override
    public String getMemoryKey() {
        return this.memoryKey;
    }

    @Override
    public String toString() {
        return StringFactory.mapReduceString(this, this.memoryKey);
    }

    //////////////////////////////

    public static Builder build() {
        return new Builder();
    }

    public final static class Builder {

        private String memoryKey = DEFAULT_MEMORY_KEY;

        private Builder() {

        }

        public Builder memoryKey(final String memoryKey) {
            this.memoryKey = memoryKey;
            return this;
        }

        public PageRankMapReduce create() {
            return new PageRankMapReduce(this.memoryKey);
        }

    }
}