需求：求IP訪問次數(shù)的TopN
1) 獲取ip => (ip,1)
2）reduceByKey(+)
3）排序 sortBy
object test {
def main(args: Array[String]): Unit = {
val sparkConf = new SparkConf().setAppName("test").setMaster("local[2]")
val sc = new SparkContext(sparkConf)
val lines = sc.textFile("file:///E:/BigDataSoftware/data/baidu.log")
lines.map(x=> {
val tmp = x.split("\t")
(tmp(5),1) //取出IP這一列脑溢，并轉換成tuple類型（IP,1）
}).reduceByKey(_+_).sortBy(_._2,false).take(N)
sc.stop()
}
}
sortBy默認是升序，sortBy(_._2,false)指的是按降序排列赖欣，下面是sortBy的源碼
/**
* Return this RDD sorted by the given key function.
*/
def sortBy[K](
f: (T) => K,
ascending: Boolean = true,
numPartitions: Int = this.partitions.length)
(implicit ord: Ordering[K], ctag: ClassTag[K]): RDD[T] = withScope {
this.keyBy[K](f)
.sortByKey(ascending, numPartitions)
.values
}
