Scala实验4.1
请到本教程官网的“下载专区”的“数据集”中下载 chapter5-data1.txt，该数据集包含
了某大学计算机系的成绩，数据格式如下所示：
Tom,DataBase,80
Tom,Algorithm,50
Tom,DataStructure,60
Jim,DataBase,90
Jim,Algorithm,60
Jim,DataStructure,80
（1） 该系总共有多少学生；
val lines = sc.textFile("file:///usr/local/spark/sparksqldata/Data01.txt")
val par = lines.map(row=>row.split(",")(0))
val distinct_par = par.distinct() //去重操作
distinct_par.count //取得总数
（2） 该系共开设来多少门课程；
val lines = sc.textFile("file:///usr/local/spark/sparksqldata/Data01.txt")
val par = lines.map(row=>row.split(",")(1))
val distinct_par = par.distinct()
distinct_par.count
（3） Tom 同学的总成绩平均分是多少；
val lines = sc.textFile("file:///usr/local/spark/sparksqldata/Data01.txt")
val pare = lines.filter(row=>row.split(",")(0)=="Tom")
pare.foreach(println)
Tom,DataBase,26
Tom,Algorithm,12
Tom,OperatingSystem,16
Tom,Python,40
Tom,Software,60
pare.map(row=>(row.split(",")(0),row.split(",")(2).toInt)).mapValues(x=>(x,1)).reduceByKey((x,y
) => (x._1+y._1,x._2 + y._2)).mapValues(x => (x._1 / x._2)).collect()
//res9: Array[(String, Int)] = Array((Tom,30))
（4） 求每名同学的选修的课程门数；
val lines = sc.textFile("file:///usr/local/spark/sparksqldata/Data01.txt")
val pare = lines.map(row=>(row.split(",")(0),row.split(",")(1)))
pare.mapValues(x => (x,1)).reduceByKey((x,y) => (" ",x._2 + y._2)).mapValues(x =>
x._2).foreach(println)
（5） 该系 DataBase 课程共有多少人选修；
val lines = sc.textFile("file:///usr/local/spark/sparksqldata/Data01.txt")
val pare = lines.filter(row=>row.split(",")(1)=="DataBase")
pare.count
res1: Long = 126
（6） 各门课程的平均分是多少；
val lines = sc.textFile("file:///usr/local/spark/sparksqldata/Data01.txt")
val pare = lines.map(row=>(row.split(",")(1),row.split(",")(2).toInt))
pare.mapValues(x=>(x,1)).reduceByKey((x,y) => (x._1+y._1,x._2 + y._2)).mapValues(x => (x._1/ x._2)).collect()
（7）使用累加器计算共有多少人选了 DataBase 这门课。
val lines = sc.textFile("file:///usr/local/spark/sparksqldata/Data01.txt")
val pare = lines.filter(row=>row.split(",")(1)=="DataBase").map(row=>(row.split(",")(1),1))
val accum = sc.longAccumulator("My Accumulator")
pare.values.foreach(x => accum.add(x))
accum.value
res19: Long = 126
