I'm using Spark 2.2 and am running into troubles when attempting to call spark.createDataset
on a Seq
of Map
.
Code and output from my Spark Shell session follow:
// 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)))
I've tried import spark.implicits._
, though I'm fairly certain that's implicitly imported by the Spark shell session.
Is this is a case not covered by current encoders?
See Question&Answers more detail:
os 与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…