拿一个统计单词为例

sortBy：

sortBy可以定义排序方式

object sortByTest{
  def main(args: Array[String]): Unit = {
    val conf: SparkConf = new SparkConf().setMaster("local[*]").setAppName("reduceTest")
    val sc = new SparkContext(conf)
    val lines: RDD[String] = sc.parallelize(Array("hello java","hello spark","hello scala"))
    val word: RDD[String] = lines.flatMap(_.split(" "))
    val A: RDD[(String, Int)] = word.map((_,1))
    val B: RDD[(String, Int)] = A.reduceByKey(_+_)
    val C: RDD[(String, Int)] = B.sortBy(_._2,false)
    C.foreach(println)
  }
}

这里我们用_._2,意思是根据value值来排序，比如（hello,1），根据这个键值对来用1排序，后面的false表示降序排列，不加默认升序排列。

sortByKey：

它会根据key来进行排序，我们来看代码

object sortByKeyTest{
  def main(args: Array[String]): Unit = {
    val conf: SparkConf = new SparkConf().setMaster("local[*]").setAppName("reduceTest")
    val sc = new SparkContext(conf)
    val lines: RDD[String] = sc.parallelize(Array("hello java","hello spark","hello scala"))
    val word: RDD[String] = lines.flatMap(_.split(" "))
    val A: RDD[(String, Int)] = word.map((_,1))
    val B: RDD[(String, Int)] = A.reduceByKey(_+_)
    val C: RDD[(String, Int)] = B.sortByKey()
    C.foreach(println)
  }
}

会根据键值对的key进行排序，下面看一种用swap反转用sortbykey来对value排序

object sortByKeyTest{
  def main(args: Array[String]): Unit = {
    val conf: SparkConf = new SparkConf().setMaster("local[*]").setAppName("reduceTest")
    val sc = new SparkContext(conf)
    val lines: RDD[String] = sc.parallelize(Array("hello java","hello spark","hello scala"))
    val word: RDD[String] = lines.flatMap(_.split(" "))
    val A: RDD[(String, Int)] = word.map((_,1))
    val B: RDD[(String, Int)] = A.reduceByKey(_+_)
    val C: RDD[(Int, String)] = B.map(_.swap)
    val D: RDD[(Int, String)] = C.sortByKey(false)
    val E: RDD[(String, Int)] = D.map(_.swap)
    E.foreach(println)
  }
}

调用swap方法将键值对的key，value反转，变成（3，hello），然后在进行sortbykey，排完序以后再swap反转