大数据入门到精通3-SPARK RDD filter 以及 filter 函数

一。如何处理RDD的filter

1. 把第一行的行头去掉

scala> val collegesRdd= sc.textFile("/user/hdfs/CollegeNavigator.csv")
collegesRdd: org.apache.spark.rdd.RDD[String] = /user/hdfs/CollegeNavigator.csv MapPartitionsRDD[3] at textFile at <console>:24

scala> collegesRdd.count
res1: Long = 504

scala> val header= collegesRdd.first
header: String = "Name","Address","Website","Type","Awards offered","Campus setting","Campus housing","Student population","Undergraduate students","Graduation Rate","Transfer-Out Rate","Cohort Year *","Net Price **","Largest Program","IPEDS ID","OPE ID"

scala> val headerlessRdd= collegesRdd.filter( line=>{ line!= header } )
headerlessRdd: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[2] at filter at <console>:28

这里其实已经使用了一个filter，就是过滤行头的filter。

val filterRdd= headerlessRdd.filter(line =>{

val count=line.split("\",\"")(7)

val len=count.length()

len>4

})

scala> filterRdd.count
res8: Long = 121

得到学生数目大于10000的学校

二、写filter函数

上面的例子也可以写一个filter函数

def  filterfunc(line :String):Boolean ={
val count=line.split("\",\"")(7)
val len=count.length()
len > 4
}

val filterRdd2=headerlessRdd.filter(filterfunc)

会得出如下结果

scala> filterRdd2.count

18/11/20 03:41:33 WARN spark.ExecutorAllocationManager: No stages are running, but numRunningTasks != 0
res10: Long = 121

补充说明一个字符串被split以后是一个字符数组，所有的字符操作参加scala的字符串操作

https://www.yiibai.com/scala/scala_strings.html

或者scala官方网站

https://www.scala-lang.org/