SparkSQL编程之DataSet

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DataSet

Dataset是具有强类型的数据集合，需要提供对应的类型信息。

 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]

 

 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()

2.3.3 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