我正在使用 Spark 2.2,在尝试spark.createDataset
调用Seq
.Map
我的 Spark Shell 会话的代码和输出如下:
// createDataSet on Seq[T] where T = Int works
scala> spark.createDataset(Seq(1, 2, 3)).collect
res0: Array[Int] = Array(1, 2, 3)
scala> spark.createDataset(Seq(Map(1 -> 2))).collect
<console>:24: error: Unable to find encoder for type stored in a Dataset.
Primitive types (Int, String, etc) and Product types (case classes) are
supported by importing spark.implicits._
Support for serializing other types will be added in future releases.
spark.createDataset(Seq(Map(1 -> 2))).collect
^
// createDataSet on a custom case class containing Map works
scala> case class MapHolder(m: Map[Int, Int])
defined class MapHolder
scala> spark.createDataset(Seq(MapHolder(Map(1 -> 2)))).collect
res2: Array[MapHolder] = Array(MapHolder(Map(1 -> 2)))
我试过import spark.implicits._
了,虽然我相当肯定这是由 Spark shell 会话隐式导入的。
这是当前编码器未涵盖的情况吗?