198、Spark 2.0之Dataset开发详解-聚合函数：c

collect_list和collect_set，都用于将同一个分组内的指定字段的值串起来，变成一个数组
常用于行转列
比如说
depId=1, employee=leo
depId=1, employee=jack
depId=1, employees=[leo, jack]

代码

object AggregateFunction {

  case class Employee(name: String, age: Long, depId: Long, gender: String, salary: Long)

  case class Department(id: Long, name: String)

  def main(args: Array[String]): Unit = {
    val sparkSession = SparkSession
      .builder()
      .appName("AggregateFunction")
      .master("local")
      .getOrCreate()

    import sparkSession.implicits._
    import org.apache.spark.sql.functions._

    val employeePath = this.getClass.getClassLoader.getResource("employee.json").getPath
    val departmentPath = this.getClass.getClassLoader.getResource("department.json").getPath

    val employeeDF = sparkSession.read.json(employeePath)
    val departmentDF = sparkSession.read.json(departmentPath)

    val employeeDS = employeeDF.as[Employee]
    val departmentDS = departmentDF.as[Department]

    employeeDS
      .groupBy(employeeDS("depId"))
      .agg(collect_set(employeeDS("name")), collect_list(employeeDS("name")))
      .collect()
      .foreach(println(_))
  }
}