1解釋

統計圖中的Triangle，並返回

原始碼：

/*
 * 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.spark.graphx.lib

import scala.reflect.ClassTag

import org.apache.spark.graphx._

/**
 * Compute the number of triangles passing through each vertex.
 *
 * The algorithm is relatively straightforward and can be computed in three steps:
 *
 * <ul>
 * <li>Compute the set of neighbors for each vertex
 * <li>For each edge compute the intersection of the sets and send the count to both vertices.
 * <li> Compute the sum at each vertex and divide by two since each triangle is counted twice.
 * </ul>
 *
 * Note that the input graph should have its edges in canonical direction
 * (i.e. the `sourceId` less than `destId`). Also the graph must have been partitioned
 * using [[org.apache.spark.graphx.Graph#partitionBy]].
 */
object TriangleCount {

  def run[VD: ClassTag, ED: ClassTag](graph: Graph[VD, ED]): Graph[Int, ED] = {
    // Remove redundant edges
    val g = graph.groupEdges((a, b) => a).cache()

    // Construct set representations of the neighborhoods
    val nbrSets: VertexRDD[VertexSet] =
      g.collectNeighborIds(EdgeDirection.Either).mapValues { (vid, nbrs) =>
        val set = new VertexSet(4)
        var i = 0
        while (i < nbrs.size) {
          // prevent self cycle
          if (nbrs(i) != vid) {
            set.add(nbrs(i))
          }
          i += 1
        }
        set
      }
    // join the sets with the graph
    val setGraph: Graph[VertexSet, ED] = g.outerJoinVertices(nbrSets) {
      (vid, _, optSet) => optSet.getOrElse(null)
    }
    // Edge function computes intersection of smaller vertex with larger vertex
    def edgeFunc(ctx: EdgeContext[VertexSet, ED, Int]) {
      assert(ctx.srcAttr != null)
      assert(ctx.dstAttr != null)
      val (smallSet, largeSet) = if (ctx.srcAttr.size < ctx.dstAttr.size) {
        (ctx.srcAttr, ctx.dstAttr)
      } else {
        (ctx.dstAttr, ctx.srcAttr)
      }
      val iter = smallSet.iterator
      var counter: Int = 0
      while (iter.hasNext) {
        val vid = iter.next()
        if (vid != ctx.srcId && vid != ctx.dstId && largeSet.contains(vid)) {
          counter += 1
        }
      }
      ctx.sendToSrc(counter)
      ctx.sendToDst(counter)
    }
    // compute the intersection along edges
    val counters: VertexRDD[Int] = setGraph.aggregateMessages(edgeFunc, _ + _)
    // Merge counters with the graph and divide by two since each triangle is counted twice
    g.outerJoinVertices(counters) {
      (vid, _, optCounter: Option[Int]) =>
        val dblCount = optCounter.getOrElse(0)
        // double count should be even (divisible by two)
        assert((dblCount & 1) == 0)
        dblCount / 2
    }
  } // end of TriangleCount
}
 

outerJoinVertices

2.程式碼：

/**
 * @author xubo
 * ref http://spark.apache.org/docs/1.5.2/graphx-programming-guide.html
 * time 20160503
 */

package org.apache.spark.graphx.learning

import org.apache.spark.SparkConf
import org.apache.spark.SparkContext
import org.apache.spark.graphx.Graph
import org.apache.spark.graphx.Graph.graphToGraphOps
import org.apache.spark.graphx.VertexId
import org.apache.spark.graphx.util.GraphGenerators
import org.apache.spark.graphx.GraphLoader
import org.apache.spark.graphx.PartitionStrategy

object TriangleCounting {

  def main(args: Array[String]): Unit = {
    val conf = new SparkConf().setAppName("ConnectedComponents").setMaster("local[4]")
    val sc = new SparkContext(conf)

    // Load the edges in canonical order and partition the graph for triangle count
    val graph = GraphLoader.edgeListFile(sc, "file/data/graphx/input/followers.txt", true).partitionBy(PartitionStrategy.RandomVertexCut)
    // Find the triangle count for each vertex
    val triCounts = graph.triangleCount().vertices
    // Join the triangle counts with the usernames
    val users = sc.textFile("file/data/graphx/input/users.txt").map { line =>
      val fields = line.split(",")
      (fields(0).toLong, fields(1))
    }
    val triCountByUsername = users.join(triCounts).map {
      case (id, (username, tc)) =>
        (username, tc)
    }
    // Print the result 
    println("\ngraph edges");
    println("edges:");
    graph.edges.collect.foreach(println)
    graph.edges.collect.foreach(println)
    println("vertices:");
    graph.vertices.collect.foreach(println)
    println("triplets:");
    graph.triplets.collect.foreach(println)
    println("\nusers");
    users.collect.foreach(println)
    
    println("\n triCounts:");
    triCounts.collect.foreach(println)
    println("\n triCountByUsername:");
    println(triCountByUsername.collect().mkString("\n"))

  }
}
 

3.結果：

graph edges
edges:
Edge(1,2,1)
Edge(1,2,1)
Edge(1,4,1)
Edge(3,6,1)
Edge(3,7,1)
Edge(3,7,1)
Edge(6,7,1)
Edge(6,7,1)
Edge(1,2,1)
Edge(1,2,1)
Edge(1,4,1)
Edge(3,6,1)
Edge(3,7,1)
Edge(3,7,1)
Edge(6,7,1)
Edge(6,7,1)
vertices:
(4,1)
(6,1)
(2,1)
(1,1)
(3,1)
(7,1)
triplets:
((1,1),(2,1),1)
((1,1),(2,1),1)
((1,1),(4,1),1)
((3,1),(6,1),1)
((3,1),(7,1),1)
((3,1),(7,1),1)
((6,1),(7,1),1)
((6,1),(7,1),1)

users
(1,BarackObama)
(2,ladygaga)
(3,jeresig)
(4,justinbieber)
(6,matei_zaharia)
(7,odersky)
(8,anonsys)

 triCounts:
(4,0)
(6,1)
(2,0)
(1,0)
(3,1)
(7,1)

 triCountByUsername:
(justinbieber,0)
(matei_zaharia,1)
(ladygaga,0)
(BarackObama,0)
(jeresig,1)
(odersky,1)
 

在followers中加入2 4這條邊後，結果為：

 triCounts:
(4,1)
(6,1)
(2,1)
(1,1)
(3,1)
(7,1)

 triCountByUsername:
(justinbieber,1)
(matei_zaharia,1)
(ladygaga,1)
(BarackObama,1)
(jeresig,1)
(odersky,1)

參考

【1】 http://spark.apache.org/docs/1.5.2/graphx-programming-guide.html