Spark下的PageRank实现

val sc = new SparkContext(...)
val links = sc.parallelize(Array(('A',Array('D')),('B',Array('A')),('C',Array('A','B')),('D',Array('A','C'))),2).map(x => (x._1,x._2)).cache()

var ranks = sc.parallelize(Array(('A',1.0),('B',1.0),('C',1.0),('D',1.0)),2)

val iterations_num = 50

for(i <- 1 to iterations_num){
	val contribs = links.join(ranks,2).flatMap{
		case(url,(links,rank)) => links.map(dest => (dest,rank/links,size))
	}

	ranks = contribs.reduceByKey(_ + _,2).mapValues(0.15 + 0.85 * _)
}

ranks.saveAsTextFile(...)