Scala Spark 数据集更改 class 类型

Question

我有一个数据框，我将其创建为 MyData1 的架构，然后我创建了一个列，以便新数据框遵循 MyData2 的架构。现在我想 return 将新数据帧作为数据集，但出现以下错误：

[info]   org.apache.spark.sql.AnalysisException: cannot resolve '`hashed`' given input columns: [id, description];
[info]   at org.apache.spark.sql.catalyst.analysis.package$AnalysisErrorAt.failAnalysis(package.scala:42)
[info]   at org.apache.spark.sql.catalyst.analysis.CheckAnalysis$$anonfun$checkAnalysis$$anonfun$apply.applyOrElse(CheckAnalysis.scala:110)
[info]   at org.apache.spark.sql.catalyst.analysis.CheckAnalysis$$anonfun$checkAnalysis$$anonfun$apply.applyOrElse(CheckAnalysis.scala:107)
[info]   at org.apache.spark.sql.catalyst.trees.TreeNode$$anonfun$transformUp.apply(TreeNode.scala:278)
[info]   at org.apache.spark.sql.catalyst.trees.TreeNode$$anonfun$transformUp.apply(TreeNode.scala:278)

这是我的代码：

import org.apache.spark.sql.{DataFrame, Dataset}

case class MyData1(id: String, description: String)


case class MyData2(id: String, description: String, hashed: String) 

object MyObject {

    def read(arg1: String, arg2: String): Dataset[MyData2] {
        var df: DataFrame = null
        val obj1 = new Matcher("cbutrer383", "e8f8chsdfd")
        val obj2 = new Matcher("cbutrer383", "g567g4rwew")
        val obj3 = new Matcher("cbutrer383", "567yr45e45")
        df = Seq(obj1, obj2, obj3).toDF("id", "description")

        df.withColumn("hashed", lit("hash"))

        val ds: Dataset[MyData2] = df.as[MyData2]
        ds
    }
}

我知道下一行可能有问题，但我想不通

val ds: Dataset[MyData2] = df.as[MyData2]

我是新手，所以可能犯了一个基本错误。任何人都可以帮忙吗？ TIA

Answer 1

您忘记将新创建的 Dataframe 分配给 df

df = df.withColumn("hashed", lit("hash"))

withcolumn Spark 文档说

Returns a new Dataset by adding a column or replacing the existing column that has the same name.

Answer 2

你的阅读功能的更好版本如下，

尽量避免 null 赋值，var，return 语句并不是真正需要的

def read(arg1: String, arg2: String): Dataset[MyData2] = {
  val obj1 = new Matcher("cbutrer383", "e8f8chsdfd")
  val obj2 = new Matcher("cbutrer383", "g567g4rwew")
  val obj3 = new Matcher("cbutrer383", "567yr45e45")
  Seq(obj1, obj2, obj3).toDF("id", "description")
    .withColumn("hashed", lit("hash"))
    .as[MyData2]
}

Scala Spark 数据集更改 class 类型

Scala Spark Dataset change class type

scala

apache-spark

apache-spark-sql

apache-spark-dataset