How to convert a dataframe to dataset in Apache Spark in Scala?

问题

I need to convert my dataframe to a dataset and I used the following code:

    val final_df = Dataframe.withColumn(
      "features",
      toVec4(
        // casting into Timestamp to parse the string, and then into Int
        $"time_stamp_0".cast(TimestampType).cast(IntegerType),
        $"count",
        $"sender_ip_1",
        $"receiver_ip_2"
      )
    ).withColumn("label", (Dataframe("count"))).select("features", "label")

    final_df.show()

    val trainingTest = final_df.randomSplit(Array(0.3, 0.7))
    val TrainingDF = trainingTest(0)
    val TestingDF=trainingTest(1)
    TrainingDF.show()
    TestingDF.show()

    ///lets create our liner regression
    val lir= new LinearRegression()
    .setRegParam(0.3)
    .setElasticNetParam(0.8)
    .setMaxIter(100)
    .setTol(1E-6)

    case class df_ds(features:Vector, label:Integer)
    org.apache.spark.sql.catalyst.encoders.OuterScopes.addOuterScope(this)

    val Training_ds = TrainingDF.as[df_ds]

My problem is that, I got the following error:

Error:(96, 36) 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.
    val Training_ds = TrainingDF.as[df_ds]

It seems that the number of values in dataframe is different with the number of value in my class. However I am using case class df_ds(features:Vector, label:Integer) on my TrainingDF dataframe since, It has a vector of features and an integer label. Here is TrainingDF dataframe:

+--------------------+-----+
|            features|label|
+--------------------+-----+
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,19...|   19|
|[1.497325796E9,10...|   10|
+--------------------+-----+

Also here is my original final_df dataframe:

+------------+-----------+-------------+-----+
|time_stamp_0|sender_ip_1|receiver_ip_2|count|
+------------+-----------+-------------+-----+
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.2|     10.0.0.3|   19|
|    05:49:56|   10.0.0.3|     10.0.0.2|   10|
+------------+-----------+-------------+-----+

However I got the mentioned error! Can anybody help me? Thanks in advance.

回答1:

The error message you are reading is a pretty good pointer.

When you convert a DataFrame to a Dataset you have to have a proper Encoder for whatever is stored in the DataFrame rows.

Encoders for primitive-like types (Ints, Strings, and so on) and case classes are provided by just importing the implicits for your SparkSession like follows:

case class MyData(intField: Int, boolField: Boolean) // e.g.

val spark: SparkSession = ???
val df: DataFrame = ???

import spark.implicits._

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

If that doesn't work either is because the type you are trying to cast the DataFrame to isn't supported. In that case, you would have to write your own Encoder: you may find more information about it here and see an example (the Encoder for java.time.LocalDateTime) here.

回答2:

Spark 1.6.0

case class MyCase(id: Int, name: String)

val encoder = org.apache.spark.sql.catalyst.encoders.ExpressionEncoder[MyCase]

val dataframe = …

val dataset = dataframe.as(encoder)

Spark 2.0 or above

case class MyCase(id: Int, name: String)

val encoder = org.apache.spark.sql.Encoders.product[MyCase]

val dataframe = …

val dataset = dataframe.as(encoder)

来源：https://stackoverflow.com/questions/44516627/how-to-convert-a-dataframe-to-dataset-in-apache-spark-in-scala

标签

scala

apache-spark

apache-spark-sql

apache-spark-encoders