// 聚合操作
    println("*************************************************************")
    println("聚合操作")
    println("*************************************************************")
    println("找出年纪最大的追求者:")
    val oldestFollower:VertexRDD[(String,Int)] = userGraph.mapReduceTriplets[(String,Int)](
      // 将源顶点的属性发送给目标顶点,map过程
      edge => Iterator((edge.dstId,(edge.srcAttr.name,edge.srcAttr.age))),
      // 得到最大追求者,reduce过程
      (a,b) => if(a._2>b._2) a else b
    )
    userGraph.vertices.leftJoin(oldestFollower){(id,user,optOldestFollower) =>
      optOldestFollower match{
        case None => s"${user.name} does not have any followers."
        case Some(oldestAge) => s"The oldest age of ${user.name} \‘s followers is ${oldestAge._2}(${oldestAge._1})."
      }
    }.collect.foreach{case(id,str) => println(str)}
    println

    // 找出追求者的平均年龄
    println("找出追求者的平均年龄:")
    val averageAge:VertexRDD[Double] = userGraph.mapReduceTriplets[(Int,Double)](
      // 将源顶点的属性(1,Age)发送给目标顶点,map过程
      edge => Iterator((edge.dstId,(1,edge.srcAttr.age.toDouble))),
      // 得到追求者的数量和总年龄
      (a,b) => ((a._1+b._1),(a._2+b._2))
    ).mapValues((id,p) => p._2/p._1)

    userGraph.vertices.leftJoin(averageAge){(id,user,optAverageAge) =>
      optAverageAge match{
        case None => s"${user.name} does not have any followers."
        case Some(avgAge) => s"The average age of ${user.name} \‘s followers is $avgAge."
      }
    }.collect.foreach{case(id,str) => println(str)}
    println

    // 聚合操作2
    println("*************************************************************")
    println("聚合操作2")
    println("*************************************************************")
    println("找出3到各顶点的最短距离:")
    // 定义源点
    val sourceId:VertexId = 3L
    val initialGraph = graph.mapVertices((id,_) => if(id==sourceId) 0.0 else Double.PositiveInfinity)
    val sssp = initialGraph.pregel(Double.PositiveInfinity)(
      (id,dist,newDist) => math.min(dist,newDist),
      // 权重计算
      triplet=>{
        if(triplet.srcAttr + triplet.attr < triplet.dstAttr){
          Iterator((triplet.dstId, triplet.srcAttr+triplet.attr))
        } else{
          Iterator.empty
        }
      },
      // 最短距离
      (a,b) => math.min(a,b)
    )
    println(sssp.vertices.collect.mkString("\n"))

*************************************************************
聚合操作
*************************************************************
找出年纪最大的追求者:
The oldest age of Peter ‘s followers is 27(Henry).
The oldest age of Kate ‘s followers is 55(Charlie).
The oldest age of Henry ‘s followers is 55(Charlie).
The oldest age of Alice ‘s followers is 32(Peter).
The oldest age of Charlie ‘s followers is 35(Mike).
Mike does not have any followers.

找出追求者的平均年龄:
The average age of Peter ‘s followers is 27.0.
The average age of Kate ‘s followers is 45.0.
The average age of Henry ‘s followers is 45.0.
The average age of Alice ‘s followers is 29.5.
The average age of Charlie ‘s followers is 35.0.
Mike does not have any followers.

*************************************************************
聚合操作2
*************************************************************
找出3到各顶点的最短距离:
(4,9.0)
(6,3.0)
(2,7.0)
(1,10.0)
(3,0.0)
(5,Infinity)