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https://issues.apache.org/jira/browse/SPARK-37476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17452101#comment-17452101
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koert kuipers edited comment on SPARK-37476 at 12/2/21, 12:58 AM:
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i get that scala Double cannot be null. however i dont understand how this is
relevant? my case class can be null, yet it fails when i try to return null for
the case class. in so far i know a nullable struct is perfectly valid in spark?
was (Author: koert):
i get that scala Double cannot be null. however i dont understand how this is
relevant? my case class can be null, yet it fails when i try to return null for
the case class.
> udaf doesnt work with nullable (or option of) case class result
> ----------------------------------------------------------------
>
> Key: SPARK-37476
> URL: https://issues.apache.org/jira/browse/SPARK-37476
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 3.2.0
> Environment: spark master branch on nov 27
> Reporter: koert kuipers
> Priority: Minor
>
> i have a need to have a dataframe aggregation return a nullable case class.
> there seems to be no way to get this to work. the suggestion to wrap the
> result in an option doesnt work either.
> first attempt using nulls:
> {code:java}
> case class SumAndProduct(sum: Double, product: Double)
> val sumAndProductAgg = new Aggregator[Double, SumAndProduct, SumAndProduct] {
> def zero: SumAndProduct = null
> def reduce(b: SumAndProduct, a: Double): SumAndProduct =
> if (b == null) {
> SumAndProduct(a, a)
> } else {
> SumAndProduct(b.sum + a, b.product * a)
> }
> def merge(b1: SumAndProduct, b2: SumAndProduct): SumAndProduct =
> if (b1 == null) {
> b2
> } else if (b2 == null) {
> b1
> } else {
> SumAndProduct(b1.sum + b2.sum, b1.product * b2.product)
> }
> def finish(r: SumAndProduct): SumAndProduct = r
> def bufferEncoder: Encoder[SumAndProduct] = ExpressionEncoder()
> def outputEncoder: Encoder[SumAndProduct] = ExpressionEncoder()
> }
> val df = Seq.empty[Double]
> .toDF()
> .select(udaf(sumAndProductAgg).apply(col("value")))
> df.printSchema()
> df.show()
> {code}
> this gives:
> {code:java}
> root
> |-- $anon$3(value): struct (nullable = true)
> | |-- sum: double (nullable = false)
> | |-- product: double (nullable = false)
> 16:44:54.882 ERROR org.apache.spark.executor.Executor: Exception in task 0.0
> in stage 1491.0 (TID 1929)
> java.lang.RuntimeException: Error while encoding:
> java.lang.NullPointerException: Null value appeared in non-nullable field:
> top level Product or row object
> If the schema is inferred from a Scala tuple/case class, or a Java bean,
> please try to use scala.Option[_] or other nullable types (e.g.
> java.lang.Integer instead of int/scala.Int).
> knownnotnull(assertnotnull(input[0, org.apache.spark.sql.SumAndProduct,
> true])).sum AS sum#20070
> knownnotnull(assertnotnull(input[0, org.apache.spark.sql.SumAndProduct,
> true])).product AS product#20071
> at
> org.apache.spark.sql.errors.QueryExecutionErrors$.expressionEncodingError(QueryExecutionErrors.scala:1125)
> {code}
> i dont really understand the error, this result is not a top-level row object.
> anyhow taking the advice to heart and using option we get to the second
> attempt using options:
> {code:java}
> case class SumAndProduct(sum: Double, product: Double)
> val sumAndProductAgg = new Aggregator[Double, Option[SumAndProduct],
> Option[SumAndProduct]] {
> def zero: Option[SumAndProduct] = None
> def reduce(b: Option[SumAndProduct], a: Double): Option[SumAndProduct] =
> b
> .map{ b => SumAndProduct(b.sum + a, b.product * a) }
> .orElse{ Option(SumAndProduct(a, a)) }
> def merge(b1: Option[SumAndProduct], b2: Option[SumAndProduct]):
> Option[SumAndProduct] =
> b1.map{ b1 =>
> b2.map{ b2 =>
> SumAndProduct(b1.sum + b2.sum, b1.product * b2.product)
> }.getOrElse(b1)
> }.orElse(b2)
> def finish(r: Option[SumAndProduct]): Option[SumAndProduct] = r
> def bufferEncoder: Encoder[Option[SumAndProduct]] = ExpressionEncoder()
> def outputEncoder: Encoder[Option[SumAndProduct]] = ExpressionEncoder()
> }
> val df = Seq.empty[Double]
> .toDF()
> .select(udaf(sumAndProductAgg).apply(col("value")))
> df.printSchema()
> df.show()
> {code}
> this gives:
> {code:java}
> root
> |-- $anon$4(value): struct (nullable = true)
> | |-- sum: double (nullable = false)
> | |-- product: double (nullable = false)
> 16:44:54.998 ERROR org.apache.spark.executor.Executor: Exception in task 0.0
> in stage 1493.0 (TID 1930)
> java.lang.AssertionError: index (1) should < 1
> at
> org.apache.spark.sql.catalyst.expressions.UnsafeRow.assertIndexIsValid(UnsafeRow.java:142)
> at
> org.apache.spark.sql.catalyst.expressions.UnsafeRow.isNullAt(UnsafeRow.java:338)
> at
> org.apache.spark.sql.catalyst.expressions.GeneratedClass$SpecificUnsafeProjection.apply(Unknown
> Source)
> at
> org.apache.spark.sql.execution.aggregate.AggregationIterator.$anonfun$generateResultProjection$5(AggregationIterator.scala:260)
> at
> org.apache.spark.sql.execution.aggregate.ObjectAggregationIterator.outputForEmptyGroupingKeyWithoutInput(ObjectAggregationIterator.scala:107)
> {code}
>
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