spark: rdd的應用(scala api)

1. wordcount: 統計詞頻， 排序
2. 歷年溫度最值： max, min, avg

part1: spark rdd 之 wordcount

spark-shell

//word.txt
var file="/home/wang/txt/word.txt" //a b c e f e f
import  org.apache.spark.rdd.RDD 

var rdd1:RDD[String]=sc.textFile(file)     				 // a b c e f e f
var rdd2:RDD[(String,Integer)]=rdd1.flatMap(_.split(" ") ).filter(_.trim !="" ).map((_,1))   // ("",6) (a,1)
var rdd3:RDD[(String,Integer)] =rdd2.reduceByKey(_+_)   //(b,1), (yre,1), (46,1)
var arr=rdd3.collect									

//按單詞升序
var wordsRdd:RDD[(String,Integer)]=rdd3.sortByKey(true) // (435,1), (46,1), (5,1), (:,1), (a,1)
var arr1:Array[(String,Integer)]=wordsRdd.collect		
//按詞頻降序
var countRdd:RDD[(String,Integer)]=rdd3.sortBy(x=>x._2,false) // (e,4), (f,2), (er,2)
var arr2:Array[(String,Integer)]=countRdd.collect		

scala api

<!--maven依賴 -->
	<dependency>
            <groupId>org.apache.spark</groupId>
            <artifactId>spark-core_2.11</artifactId>
            <version>2.1.0</version>
        </dependency>

object Wc {
  def main(args: Array[String]): Unit = {
    //conf
    var conf=new SparkConf()
    conf.setMaster("local")
    conf.setAppName("wc")

    //context
    var sc=new SparkContext(conf)
    //上面的spark-shell代碼.......
  }
}

part2: spark rdd 之 maxTemp

思路1：groupByKey

//（ 年， 溫度）=> groupByKey
//tmp.txt
var file="/home/wang/txt/tmp.txt"  //1982,-8  
import org.apache.spark.rdd.RDD

var rdd1:RDD[(Integer,Integer)]=sc.textFile(file).map(x=> 
{ var arr=x.split(",");
 (arr(0).toInt, arr(1).toInt)  //(1982,-8)
  })
//rdd2:RDD[(Integer, Iterable[Integer])]
var rdd2:RDD[(Integer,Iterable[Integer])]=rdd1.groupByKey   //(1984,CompactBuffer(-4, 26))

//(1984,26,-4,11.0),(1964,22,-11,5.5)
var rdd3:RDD[(Integer,Integer,Integer,Double)]=rdd2.map(x=>
{ var arr=x._2; 
var sum=arr.reduce(_+_);  
var avg=sum/ arr.size.toDouble; 
(x._1,  arr.max,arr.min,  avg )
})
var arr:Array[(Integer,Integer,Integer,Double)]=rdd3.collect

思路2： reduceByKey

//  (年， max溫度, min溫度, 溫度sum, 溫度count )=> reduceByKey(聚合函數)
var file="/home/wang/txt/tmp.txt"  //1982,-8  
import org.apache.spark.rdd.RDD

var rdd1:RDD[(Integer, (Integer,Integer,Integer,Integer))]=sc.textFile(file).map(x=> {
var arr=x.split(",");
var tmp=arr(1).toInt;
var year=arr(0).toInt;
(year,  (tmp, tmp,tmp, 1 )) //(1982,-8)
})

var rdd2:RDD[(Integer, (Integer,Integer,Integer,Integer))]=rdd1.reduceByKey((x,y)=>{
var tup1=x
var tup2=y

var maxTmp=max(tup1._1, tup2._1)
var minTmp=min(tup1._2, tup2._2)
var size=   tup1._3+ tup2._3
var sum=    tup1._4 + tup2._4

(maxTmp,minTmp,size,sum)  //(1984,(26,-4,22,2))
})

var rdd3:RDD[(Integer, (Integer,Integer,Double))]=rdd2.map(x=>{
var year=x._1
var tup1=x._2

var maxTmp=tup1._1
var minTmp=tup1._2

var size= tup1._3
var sum=  tup1._4 
var avg= (sum/size.toDouble).formatted("%.3f").toDouble

(year,(maxTmp,minTmp,avg))  //(1984,(26,-4,0.091))
})

var arr:Array[(Integer,Integer,Double)]=rdd3.collect