Dataset是具有强类型的数据集合，需要提供对应的类型信息。
1 创建
1）创建一个样例类
scala> case class Person(name: String, age: Long)
defined class Person
2）创建DataSet
scala> val caseClassDS = Seq(Person("Andy", 32)).toDS()
caseClassDS: org.apache.spark.sql.Dataset[Person] = [name: string, age: bigint]
2 RDD转换为DataSet
SparkSQL能够自动将包含有case类的RDD转换成DataFrame，case类定义了table的结构，case类属性通过反射变成了表的列名。
1）创建一个RDD
scala> val peopleRDD = sc.textFile("examples/src/main/resources/people.txt")
peopleRDD: org.apache.spark.rdd.RDD[String] = examples/src/main/resources/people.txt MapPartitionsRDD[3] at textFile at <console>:27
2）创建一个样例类
scala> case class Person(name: String, age: Long)
defined class Person
3）将RDD转化为DataSet
scala> peopleRDD.map(line => {val para = line.split(",");Person(para(0),para(1).trim.toInt)}).toDS()
3 DataSet转换为RDD
调用rdd方法即可。
1）创建一个DataSet
scala> val DS = Seq(Person("Andy", 32)).toDS()
DS: org.apache.spark.sql.Dataset[Person] = [name: string, age: bigint]
2）将DataSet转换为RDD
scala> DS.rdd
res11: org.apache.spark.rdd.RDD[Person] = MapPartitionsRDD[15] at rdd at <console>:28
