Spark实现wordcount的几种方式

方法一：map + reduceByKey

package com.cw.bigdata.spark.wordcount

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

/**
  * WordCount实现第一种方式:map + reduceByKey
  *
  * @author 陈小哥cw
  * @date 2020/7/9 9:59
  */
object WordCount1 {
  def main(args: Array[String]): Unit = {
    val config: SparkConf = new SparkConf().setMaster("local[*]").setAppName("WordCount1")

    val sc: SparkContext = new SparkContext(config)

    val lines: RDD[String] = sc.textFile("in")

    lines.flatMap(_.split(" ")).map((_,1)).reduceByKey(_+_).collect().foreach(println)
  }
}

方法二:使用countByValue代替map + reduceByKey

package com.cw.bigdata.spark.wordcount

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

/**
  * WordCount实现第二种方式：使用countByValue代替map + reduceByKey
  *
  * 根据数据集每个元素相同的内容来计数。返回相同内容的元素对应的条数。(不必作用在kv格式上)
  * map(value => (value, null)).countByKey()
  *
  * @author 陈小哥cw
  * @date 2020/7/9 10:02
  */
object WordCount2 {
  def main(args: Array[String]): Unit = {
    val config: SparkConf = new SparkConf().setMaster("local[*]").setAppName("WordCount2")

    val sc: SparkContext = new SparkContext(config)

    val lines: RDD[String] = sc.textFile("in")

    lines.flatMap(_.split(" ")).countByValue().foreach(println)

  }
}

方法三:aggregateByKey或者foldByKey

package com.cw.bigdata.spark.wordcount

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

/**
  * WordCount实现第三种方式：aggregateByKey或者foldByKey
  *
  * def aggregateByKey[U: ClassTag](zeroValue: U)(seqOp: (U, V) => U,combOp: (U, U) => U): RDD[(K, U)]
  *   1.zeroValue：给每一个分区中的每一个key一个初始值；
  *   2.seqOp：函数用于在每一个分区中用初始值逐步迭代value；(分区内聚合函数)
  *   3.combOp：函数用于合并每个分区中的结果。(分区间聚合函数)
  *
  *  foldByKey相当于aggregateByKey的简化操作，seqop和combop相同
  *
  *
  * @author 陈小哥cw
  * @date 2020/7/9 10:08
  */
object WordCount3 {
  def main(args: Array[String]): Unit = {
    val config: SparkConf = new SparkConf().setMaster("local[*]").setAppName("WordCount3")

    val sc: SparkContext = new SparkContext(config)

    val lines: RDD[String] = sc.textFile("in")

    lines.flatMap(_.split(" ")).map((_, 1)).aggregateByKey(0)(_ + _, _ + _).collect().foreach(println)

    lines.flatMap(_.split(" ")).map((_, 1)).foldByKey(0)(_ + _).collect().foreach(println)

  }
}

方法四:groupByKey+map

package com.cw.bigdata.spark.wordcount

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

/**
  * WordCount实现的第四种方式：groupByKey+map
  *
  * @author 陈小哥cw
  * @date 2020/7/9 13:32
  */
object WordCount4 {
  def main(args: Array[String]): Unit = {
    val config: SparkConf = new SparkConf().setMaster("local[*]").setAppName("WordCount4")

    val sc: SparkContext = new SparkContext(config)

    val lines: RDD[String] = sc.textFile("in")

    val groupByKeyRDD: RDD[(String, Iterable[Int])] = lines.flatMap(_.split(" ")).map((_, 1)).groupByKey()

    groupByKeyRDD.map(tuple => {
      (tuple._1, tuple._2.sum)
    }).collect().foreach(println)

  }
}

方法五:Scala原生实现wordcount

package com.cw.bigdata.spark.wordcount

/**
  * Scala原生实现wordcount
  *
  * @author 陈小哥cw
  * @date 2020/7/9 14:22
  */
object WordCount5 {
  def main(args: Array[String]): Unit = {

    val list = List("cw is cool", "wc is beautiful", "andy is beautiful", "mike is cool")
    /**
      * 第一步，将list中的元素按照分隔符这里是空格拆分，然后展开
      * 先map(_.split(" "))将每一个元素按照空格拆分
      * 然后flatten展开
      * flatmap即为上面两个步骤的整合
      */

    val res0 = list.map(_.split(" ")).flatten
    val res1 = list.flatMap(_.split(" "))

    println("第一步结果")
    println(res0)
    println(res1)

    /**
      * 第二步是将拆分后得到的每个单词生成一个元组
      * k是单词名称，v任意字符即可这里是1
      */
    val res3 = res1.map((_, 1))
    println("第二步结果")
    println(res3)
    /**
      * 第三步是根据相同的key合并
      */
    val res4 = res3.groupBy(_._1)
    println("第三步结果")
    println(res4)
    /**
      * 最后一步是求出groupBy后的每个key对应的value的size大小，即单词出现的个数
      */
    val res5 = res4.mapValues(_.size)
    println("最后一步结果")
    println(res5.toBuffer)
  }
}

方法六：combineByKey

package com.cw.bigdata.spark.wordcount

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

/**
  * WordCount实现的第六种方式：combineByKey
  *
  * @author 陈小哥cw
  * @date 2020/7/9 22:55
  */
object WordCount6 {
  def main(args: Array[String]): Unit = {
    val config: SparkConf = new SparkConf().setMaster("local[*]").setAppName("combineByKey")

    val sc: SparkContext = new SparkContext(config)

    val lines: RDD[String] = sc.textFile("in")

    val mapRDD: RDD[(String, Int)] = lines.flatMap(_.split(" ")).map((_, 1))

    // combineByKey实现wordcount
    mapRDD.combineByKey(
      x => x,
      (x: Int, y: Int) => x + y,
      (x: Int, y: Int) => x + y
    ).collect().foreach(println)

  }
}