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https://issues.apache.org/jira/browse/SPARK-40601?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17610588#comment-17610588
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Apache Spark commented on SPARK-40601:
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User 'EnricoMi' has created a pull request for this issue:
https://github.com/apache/spark/pull/38036
> Improve error when cogrouping groups with mismatching key sizes
> ---------------------------------------------------------------
>
> Key: SPARK-40601
> URL: https://issues.apache.org/jira/browse/SPARK-40601
> Project: Spark
> Issue Type: Improvement
> Components: PySpark, SQL
> Affects Versions: 3.4.0
> Reporter: Enrico Minack
> Priority: Minor
>
> Cogrouping two grouped DataFrames in PySpark that have different group key
> cardinalities raises an error that is not very descriptive:
> {code:python}
> left.groupby("id", "k")
> .cogroup(right.groupby("id"))
> {code}
> {code:java}
> Traceback (most recent call last):
> py4j.protocol.Py4JJavaError: An error occurred while calling
> o726.collectToPython.
> : java.lang.IndexOutOfBoundsException: 1
> at
> scala.collection.mutable.ResizableArray.apply(ResizableArray.scala:46)
> at
> scala.collection.mutable.ResizableArray.apply$(ResizableArray.scala:45)
> at scala.collection.mutable.ArrayBuffer.apply(ArrayBuffer.scala:49)
> at
> org.apache.spark.sql.catalyst.plans.physical.HashShuffleSpec.$anonfun$createPartitioning$5(partitioning.scala:650)
> {code}
> *Note:* This is Python-specific as cogrouping with differing group key sizes
> is not possible in Scala. The respective Scala API is fully typed on the key.
> The problem is that {{EnsureRequirements.ensureDistributionAndOrdering}}
> calls into {{HashShuffleSpec.createPartitioning(clustering)}} where length of
> {{clustering}} is smaller than largest bits ({{{}v.head{}}}) in
> {{{}hashKeyPositions{}}} (EnsureRequirements.scala:159):
> {code:java}
> hashKeyPositions.map(v => clustering(v.head))
> {code}
> Possible fixes:
> # Assert identical size for group keys, and provide meaningful
> cogroup-specific error message.
> # {{EnsureRequirements}} identifies this situation and provide a meaningful
> distribution-requirements-specific error message.
> # Ideally both.
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