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三角形計數__示例程序_圖模型_大數據計算服務-阿裏雲

計算通過每個頂點的三角形個數。

算法實現需三個超步：

• 每個頂點將其ID發送給所有出邊鄰居；
• 存儲入邊和出邊鄰居並發送給出邊鄰居；
• 對每條邊計算其終點的交集數量，並求和，結果輸出到表。

將表中的輸出結果求和並除以三，即得到三角形個數。

import java.io.IOException;

import com.aliyun.odps.data.TableInfo;
import com.aliyun.odps.graph.ComputeContext;
import com.aliyun.odps.graph.Edge;
import com.aliyun.odps.graph.GraphJob;
import com.aliyun.odps.graph.GraphLoader;
import com.aliyun.odps.graph.MutationContext;
import com.aliyun.odps.graph.Vertex;
import com.aliyun.odps.graph.WorkerContext;
import com.aliyun.odps.io.LongWritable;
import com.aliyun.odps.io.NullWritable;
import com.aliyun.odps.io.Tuple;
import com.aliyun.odps.io.Writable;
import com.aliyun.odps.io.WritableRecord;

/**
 * Compute the number of triangles passing through each vertex.
 *
 * The algorithm can be computed in three supersteps:
 * I. Each vertex sends a message with its ID to all its outgoing
 * neighbors.
 * II. The incoming neighbors and outgoing neighbors are stored and
 * send to outgoing neighbors.
 * III. For each edge compute the intersection of the sets at destination
 * vertex and sum them, then output to table.
 *
 * The triangle count is the sum of output table and divide by three since
 * each triangle is counted three times.
 *
 **/
public class TriangleCount {

  public static class TCVertex extends
    Vertex<LongWritable, Tuple, NullWritable, Tuple> {

    @Override
    public void setup(
        WorkerContext<LongWritable, Tuple, NullWritable, Tuple> context)
      throws IOException {
      // collect the outgoing neighbors
      Tuple t = new Tuple();
      if (this.hasEdges()) {
        for (Edge<LongWritable, NullWritable> edge : this.getEdges()) {
          t.append(edge.getDestVertexId());
        }
      }

      this.setValue(t);
    }

    @Override
    public void compute(
        ComputeContext<LongWritable, Tuple, NullWritable, Tuple> context,
        Iterable<Tuple> msgs) throws IOException {

      if (context.getSuperstep() == 0L) {
        // sends a message with its ID to all its outgoing neighbors
        Tuple t = new Tuple();
        t.append(getId());
        context.sendMessageToNeighbors(this, t);
      } else if (context.getSuperstep() == 1L) {
        // store the incoming neighbors
        for (Tuple msg : msgs) {
          for (Writable item : msg.getAll()) {
            if (!this.getValue().getAll().contains((LongWritable)item)) {
              this.getValue().append((LongWritable)item);
            }
          }
        }

        // send both incoming and outgoing neighbors to all outgoing neighbors
        context.sendMessageToNeighbors(this, getValue());
      } else if (context.getSuperstep() == 2L) {
        // count the sum of intersection at each edge
        long count = 0;
        for (Tuple msg : msgs) {
          for (Writable id : msg.getAll()) {
            if (getValue().getAll().contains(id)) {
              count ++;
            }
          }
        }

        // output to table
        context.write(getId(), new LongWritable(count));
        this.voteToHalt();
      }
    }
  }


  public static class TCVertexReader extends
  GraphLoader<LongWritable, Tuple, NullWritable, Tuple> {

    @Override
    public void load(
        LongWritable recordNum,
        WritableRecord record,
        MutationContext<LongWritable, Tuple, NullWritable, Tuple> context)
    throws IOException {
      TCVertex vertex = new TCVertex();

      vertex.setId((LongWritable) record.get(0));

      String[] edges = record.get(1).toString().split(",");
      for (int i = 0; i < edges.length; i++) {
        try {
          long destID = Long.parseLong(edges[i]);
          vertex.addEdge(new LongWritable(destID), NullWritable.get());
        } catch(NumberFormatException nfe) {
          System.err.println("Ignore " + nfe);
        }
      }
      context.addVertexRequest(vertex);
    }
  }

  public static void main(String[] args) throws IOException {
    if (args.length < 2) {
      System.out.println("Usage: <input> <output>");
      System.exit(-1);
    }

    GraphJob job = new GraphJob();
    job.setGraphLoaderClass(TCVertexReader.class);
    job.setVertexClass(TCVertex.class);

    job.addInput(TableInfo.builder().tableName(args[0]).build());
    job.addOutput(TableInfo.builder().tableName(args[1]).build());
    long startTime = System.currentTimeMillis();
    job.run();
    System.out.println("Job Finished in "
        + (System.currentTimeMillis() - startTime) / 1000.0 + " seconds");
  }
}

最後更新：2016-05-06 10:43:10

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