如何在Map数据结构中转换Spark Scala嵌套Map？

import org.apache.spark.sql.Row
import org.apache.spark.sql.functions._

val nestedMap: Map[String, Map[String, String]] = Map(
  "key1" -> Map("nestedKey1" -> "value1", "nestedKey2" -> "value2"),
  "key2" -> Map("nestedKey3" -> "value3", "nestedKey4" -> "value4")
)

val rdd = spark.sparkContext.parallelize(Seq(Row.fromSeq(Seq(nestedMap))))

val df = spark.createDataFrame(rdd, StructType(Seq(StructField("nestedMap", MapType(StringType, MapType(StringType, StringType))))))

val flattenedDF = df.withColumn("flattenedMap", explode(map_keys($"nestedMap"))).select($"flattenedMap", $"nestedMap"($"flattenedMap").as("nestedMap"))

val nestedMapDF = flattenedDF.select($"flattenedMap", explode(map_entries($"nestedMap")).as(Seq("nestedKey", "value"))).groupBy("flattenedMap").agg(collect_list(struct($"nestedKey", $"value")).as("nestedMap"))

val result = nestedMapDF.rdd.map {
  case Row(flattenedMap: String, nestedMap: Seq[Row]) =>
    (flattenedMap, nestedMap.map {
      case Row(nestedKey: String, value: String) => (nestedKey, value)
    }.toMap)
}.collect().toMap

{
  "key1": {
    "nestedKey1": "value1",
    "nestedKey2": "value2"
  },
  "key2": {
    "nestedKey3": "value3",
    "nestedKey4": "value4"
  }
}

{
  "nestedKey1": "value1",
  "nestedKey2": "value2",
  "nestedKey3": "value3",
  "nestedKey4": "value4"
}