scala高阶函数之map

统计一个文件中单词个数， 最传统的写法

package day3
import scala.collection.mutable
import scala.io.Source

object demo_wordcount {
    def main(args: Array[String]): Unit = {
        // 读取文件内容
        val linesInterator = Source.fromFile("D:\scalas\wordc.txt").getLines()
        // 统计单词出现次数, 定义可变map
        val map = mutable.Map[String, Int]()
        for(line <- linesInterator){
            // 分割字符串
            val words = line.split("\s+")
            for(word <- words){
                // 开始时map中是空值
                val cntOption = map.get(word)
                if(cntOption.isDefined){
                    val cnt = cntOption.get +1
                    map.put(word, cnt)
                }else map.put(word,1)
            }
        }
        // 打印生成的map
        for((k, v) <- map){
            println(s"${k}-->${v}")
        }
    }

}

试试函数式编程来解决

package day3

import scala.io.Source

object demo_wordcount2 {
    def main(args: Array[String]): Unit = {
        // 读取文件内容
        val linesInterator = Source.fromFile("D:\scalas\wordc.txt").getLines()
        // 切分数据
//        linesInterator.flatMap(line =>line.split("\s+"))
        val words = linesInterator.flatMap(_.split("\s+"))
        //分组
//        val groupwords = words.toArray.groupBy(word => word).foreach(t=>println(t._1 + "--->"+t._2.mkString(",")))
        val groupwords = words.toArray.groupBy(word => word)
        // 聚合 单词统计
        val wordcounts = groupwords.map(kv => (kv._1,kv._2.length))
        println(wordcounts)
    }

}

打印同样的结果 ：

Map(meimei -> 1, me -> 1, he -> 1, hello -> 4, ligang -> 1)

能不能再简单点呢， 好吧， 一句话搞定

package day3

import scala.io.Source

object demo_wordcount2 {
    def main(args: Array[String]): Unit = {
        Source.fromFile("D:\scalas\wordc.txt").getLines()
            .flatMap(_.split("\s+")).toArray
            .groupBy(word => word)
            .map(kv => (kv._1,kv._2.length))
            .foreach(println)

    }

}