如何解决Spark TopK的这个问题？

Question

我有一个关于TopK的问题要用Spark来解决。

源文件是这样的：

baoshi,13
xinxi,80
baoshi,99
xinxi,32
baoshi,50
xinxi,43
baoshi,210
xinxi,100

下面是我的代码：

import org.apache.spark.{SparkConf, SparkContext}

object TopKTest {
  def main(args: Array[String]): Unit = {
    val file = "file:///home/hadoop/rdd-test/TopK3.txt"
    val conf = new SparkConf().setAppName("TopKTest").setMaster("local")
    val sc = new SparkContext(conf)
    val txt = sc.textFile(file)
    val rdd2 =txt.map(line=>(line.split(",")(0)
      ,line.split(",")(1).trim))
    val rdd=rdd2.groupByKey()
    val rdd1 = rdd.map(line=> {
      val f = line._1
      val s = line._2
      val t = s.toList.sortWith(_ > _).take(2)
      (f, t)
})
    rdd1.foreach(println)

  }
}

预期的结果是：

(xinxi,List(100, 80))
(baoshi,List(210, 99))

Answer 1

这是因为您比较的是Strings，而不是数字。

变化

val rdd2 =txt.map(line=>(line.split(",")(0)
  ,line.split(",")(1).trim))

至

val rdd2 =txt.map(line=>(line.split(",")(0)
  ,line.split(",")(1).trim.toLong))

Answer 2

下面是方法：

scala> import org.apache.spark.mllib.rdd.MLPairRDDFunctions._
import org.apache.spark.mllib.rdd.MLPairRDDFunctions._

scala> val rdd = spark.sparkContext.textFile("D:\\test\\input.txt")
rdd: org.apache.spark.rdd.RDD[String] = D:\test\input.txt MapPartitionsRDD[1] at textFile at <console>:26

scala> rdd.foreach(println)
xinxi,43
baoshi,13
baoshi,210
xinxi,80
xinxi,100
baoshi,99
xinxi,32
baoshi,50

scala> val rdd1 = rdd.map(row => (row.split(",")(0), row.split(",")(1).toInt))
rdd1: org.apache.spark.rdd.RDD[(String, Int)] = MapPartitionsRDD[2] at map at <console>:28

scala> val rdd2 = rdd1.topByKey(2)
rdd2: org.apache.spark.rdd.RDD[(String, Array[Int])] = MapPartitionsRDD[4] at mapValues at MLPairRDDFunctions.scala:50

scala> val rdd3 = rdd2.map(m => (m._1, m._2.toList))
rdd3: org.apache.spark.rdd.RDD[(String, List[Int])] = MapPartitionsRDD[5] at map at <console>:32

scala> rdd3.foreach(println)
(xinxi,List(100, 80))
(baoshi,List(210, 99))