按火花对RDD中的值排序

Question

我有一个火花对RDD（键，计数）如下

Array[(String, Int)] = Array((a,1), (b,2), (c,1), (d,3))

使用spark scala API如何获取按值排序的新对RDD？

必需结果： Array((d,3), (b,2), (a,1), (c,1))

Answer 1

这应该工作：

//Assuming the pair's second type has an Ordering, which is the case for Int
rdd.sortBy(_._2) // same as rdd.sortBy(pair => pair._2)

（虽然你可能也想在有关系的时候把钥匙交给账户。）

Answer 2

按键和值按升序和降序排序

val textfile = sc.textFile("file:///home/hdfs/input.txt")
val words = textfile.flatMap(line => line.split(" "))
//Sort by value in descending order. For ascending order remove 'false' argument from sortBy
words.map( word => (word,1)).reduceByKey((a,b) => a+b).sortBy(_._2,false)
//for ascending order by value
words.map( word => (word,1)).reduceByKey((a,b) => a+b).sortBy(_._2)

//Sort by key in ascending order
words.map( word => (word,1)).reduceByKey((a,b) => a+b).sortByKey
//Sort by key in descending order
words.map( word => (word,1)).reduceByKey((a,b) => a+b).sortByKey(false)

这可以通过在交换键和值之后应用sortByKey以另一种方式完成

//Sort By value by swapping key and value and then using sortByKey
val sortbyvalue = words.map( word => (word,1)).reduceByKey((a,b) => a+b)
val descendingSortByvalue = sortbyvalue.sortByKey(false).map(x => (x._2,x._1))
descendingSortByvalue.toDF.show
descendingSortByvalue.foreach {n => {
val word=  n._1
val count = n._2
println(s"$word:$count")}}