CountGraphHeads.java

/*
 * Copyright © 2014 - 2021 Leipzig University (Database Research Group)
 *
 * Licensed 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.gradoop.flink.model.impl.operators.distinction.functions;

import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.util.Collector;
import org.gradoop.common.model.api.entities.GraphHead;
import org.gradoop.flink.model.api.functions.GraphHeadReduceFunction;

import java.util.Iterator;

/**
 * Distinction function that just selects the first graph head of an isomorphic group.
 *
 * @param <G> graph head type
 */
public class CountGraphHeads<G extends GraphHead> implements GraphHeadReduceFunction<G> {

  /**
   * property key to store graph count.
   */
  private final String propertyKey;

  /**
   * Constructor.
   *
   * @param propertyKey property key to store graph count.
   */
  public CountGraphHeads(String propertyKey) {
    this.propertyKey = propertyKey;
  }

  @Override
  public void reduce(Iterable<Tuple2<String, G>> iterable,
    Collector<G> collector) throws Exception {
    Iterator<Tuple2<String, G>> iterator = iterable.iterator();

    G graphHead = iterator.next().f1;
    int count = 1;

    while (iterator.hasNext()) {
      iterator.next();
      count++;
    }

    graphHead.setProperty(propertyKey, count);

    collector.collect(graphHead);
  }
}