Spark学习笔记-GraphX-1

      Spark GraphX是一个分布式图处理框架，Spark GraphX基于Spark平台提供对图计算和图挖掘简洁易用的而丰富多彩的接口，极大的方便了大家对分布式图处理的需求。Spark
GraphX由于底层是基于Spark来处理的，所以天然就是一个分布式的图处理系统。图的分布式或者并行处理其实是把这张图拆分成很多的子图，然后我们分别对这些子图进行计算，计算的时候可以分别迭代进行分阶段的计算，即对图进行并行计算。

Spark GraphX基本操作：

import org.apache.spark.SparkContext
import org.apache.spark._
import org.apache.spark.graphx._
import org.apache.spark.graphx.Graph
import org.apache.spark.graphx.Edge
import org.apache.spark.graphx.VertexRDD
import org.apache.spark.graphx.util.GraphGenerators
import org.apache.spark.graphx.GraphLoader
import org.apache.spark.storage.StorageLevel
import org.apache.spark.rdd.RDD

object SparkGraphx1 {

def main(args: Array[String]) {

val sc = new SparkContext("spark://centos.host1:7077", "Spark Graphx")

//创建点RDD
val users: RDD[(VertexId, (String, String))] = sc.parallelize(Array(
(3L, ("rxin", "student")), (7L, ("jgonzal", "postdoc")),
(5L, ("franklin", "prof")), (2L, ("istoica", "prof"))))
//创建边RDD
val relationships: RDD[Edge[String]] = sc.parallelize(Array(
Edge(3L, 7L, "collab"), Edge(5L, 3L, "advisor"),
Edge(2L, 5L, "colleague"), Edge(5L, 7L, "pi")))
//定义一个默认用户，避免有不存在用户的关系
val defaultUser = ("John Doe", "Missing")
//构造Graph
val graph = Graph(users, relationships, defaultUser)

//点RDD、边RDD过滤
val fcount1 = graph.vertices.filter { case (id, (name, pos)) => pos == "postdoc" }.count
println("postdocs users count: " + fcount1)
val fcount2 = graph.edges.filter(edge => edge.srcId > edge.dstId).count
println("srcId > dstId edges count: " + fcount2)
val fcount3 = graph.edges.filter { case Edge(src, dst, prop) => src > dst }.count
println("srcId > dstId edges count: " + fcount3)

//Triplets(三元组)，包含源点、源点属性、目标点、目标点属性、边属性
val triplets: RDD[String] = graph.triplets.map(triplet => triplet.srcId + "-" +
triplet.srcAttr._1 + "-" + triplet.attr + "-" + triplet.dstId + "-" + triplet.dstAttr._1)
triplets.collect().foreach(println(_))

//度、入度、出度
val degrees: VertexRDD[Int] = graph.degrees;
degrees.collect().foreach(println)
val inDegrees: VertexRDD[Int] = graph.inDegrees
inDegrees.collect().foreach(println)
val outDegrees: VertexRDD[Int] = graph.outDegrees
outDegrees.collect().foreach(println)

//构建子图
val subGraph = graph.subgraph(vpred = (id, attr) => attr._2 != "Missing")
subGraph.vertices.collect().foreach(println(_))
subGraph.triplets.map(triplet => triplet.srcAttr._1 + " is the " + triplet.attr + " of " + triplet.dstAttr._1)
.collect().foreach(println(_))

//Map操作，根据原图的一些特性得到新图，原图结构是不变的，下面两个逻辑是等价的，但是第一个不会被graphx系统优化
val newVertices = graph.vertices.map { case (id, attr) => (id, (attr._1 + "-1", attr._2 + "-2")) }
val newGraph1 = Graph(newVertices, graph.edges)
val newGraph2 = graph.mapVertices((id, attr) => (id, (attr._1 + "-1", attr._2 + "-2")))

//构造一个新图，顶点属性是出度
val inputGraph: Graph[Int, String] =
graph.outerJoinVertices(graph.outDegrees)((vid, _, degOpt) => degOpt.getOrElse(0))
//根据顶点属性为出度的图构造一个新图，依据PageRank算法初始化边与点
val outputGraph: Graph[Double, Double] =
inputGraph.mapTriplets(triplet => 1.0 / triplet.srcAttr).mapVertices((id, _) => 1.0)

//图的反向操作，新的图形的所有边的方向相反，不修改顶点或边性属性、不改变的边的数目，它可以有效地实现不必要的数据移动或复制
var rGraph = graph.reverse

//Mask操作也是根据输入图构造一个新图，达到一个限制制约的效果
val ccGraph = graph.connectedComponents()
val validGraph = graph.subgraph(vpred = (id, attr) => attr._2 != "Missing")
val validCCGraph = ccGraph.mask(validGraph)

//Join操作，原图外连出度点构造一个新图 ，出度为顶点属性
val degreeGraph2 = graph.outerJoinVertices(outDegrees) { (id, attr, outDegreeOpt) =>
outDegreeOpt match {
case Some(outDeg) => outDeg
case None => 0 //没有出度标识为零
}
}

//缓存。默认情况下,缓存在内存的图会在内存紧张的时候被强制清理，采用的是LRU算法
graph.cache()
graph.persist(StorageLevel.MEMORY_ONLY)
graph.unpersistVertices(true)

//GraphLoader构建Graph
var path = "/user/hadoop/data/temp/graph/graph.txt"
var minEdgePartitions = 1
var canonicalOrientation = false // if sourceId < destId this value is true
val graph1 = GraphLoader.edgeListFile(sc, path, canonicalOrientation, minEdgePartitions,
StorageLevel.MEMORY_ONLY, StorageLevel.MEMORY_ONLY)

val verticesCount = graph1.vertices.count
println(s"verticesCount: $verticesCount")
graph1.vertices.collect().foreach(println)

val edgesCount = graph1.edges.count
println(s"edgesCount: $edgesCount")
graph1.edges.collect().foreach(println)

//PageRank
val pageRankGraph = graph1.pageRank(0.001)
pageRankGraph.vertices.sortBy(_._2, false).saveAsTextFile("/user/hadoop/data/temp/graph/graph.pr")
pageRankGraph.vertices.top(5)(Ordering.by(_._2)).foreach(println)

//Connected Components
val connectedComponentsGraph = graph1.connectedComponents()
connectedComponentsGraph.vertices.sortBy(_._2, false).saveAsTextFile("/user/hadoop/data/temp/graph/graph.cc")
connectedComponentsGraph.vertices.top(5)(Ordering.by(_._2)).foreach(println)

//TriangleCount主要用途之一是用于社区发现 保持sourceId小于destId
val graph2 = GraphLoader.edgeListFile(sc, path, true)
val triangleCountGraph = graph2.triangleCount()
triangleCountGraph.vertices.sortBy(_._2, false).saveAsTextFile("/user/hadoop/data/temp/graph/graph.tc")
triangleCountGraph.vertices.top(5)(Ordering.by(_._2)).foreach(println)

sc.stop()
}

}