如何将 spark 数据框中的 WrappedArray 列转换为字符串? [英] How do I convert a WrappedArray column in spark dataframe to Strings?

问题描述

我正在尝试将包含 Array[String] 的列转换为 String，但我始终收到此错误

I am trying to convert a column which contains Array[String] to String, but I consistently get this error

org.apache.spark.SparkException: Job aborted due to stage failure: Task 0 in stage 78.0 failed 4 times, most recent failure: Lost task 0.3 in stage 78.0 (TID 1691, ip-******): java.lang.ClassCastException: scala.collection.mutable.WrappedArray$ofRef cannot be cast to [Ljava.lang.String; 

这是一段代码

val mkString = udf((arrayCol:Array[String])=>arrayCol.mkString(","))  
val dfWithString=df.select($"arrayCol").withColumn("arrayString",
      mkString($"arrayCol"))  

推荐答案

WrappedArray is not an Array (which is plain old Java Array不是原生 Scala 集合).您可以将签名更改为:

WrappedArray is not an Array (which is plain old Java Array not a natve Scala collection). You can either change signature to:

import scala.collection.mutable.WrappedArray

(arrayCol: WrappedArray[String]) => arrayCol.mkString(",")

或使用一种超类型，如 Seq:

or use one of the supertypes like Seq:

(arrayCol: Seq[String]) => arrayCol.mkString(",")

在最近的 Spark 版本中，您可以使用 concat_ws 代替:

In the recent Spark versions you can use concat_ws instead:

import org.apache.spark.sql.functions.concat_ws

df.select(concat_ws(",", $"arrayCol"))

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