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https://issues.apache.org/jira/browse/SPARK-25599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16641373#comment-16641373
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Hyukjin Kwon commented on SPARK-25599:
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Are you proposong UDAF for Python side? Then it might be a duplicate of
SPARK-10915
> Stateful aggregation in PySpark
> -------------------------------
>
> Key: SPARK-25599
> URL: https://issues.apache.org/jira/browse/SPARK-25599
> Project: Spark
> Issue Type: New Feature
> Components: PySpark
> Affects Versions: 2.3.0
> Reporter: Vincent Grosbois
> Priority: Minor
>
> Hi!
>
> From PySpark, I am trying to define a custom aggregator *that is accumulating
> state*. Is it possible in Spark 2.3 ?
> AFAIK, it is now possible to define a custom UDAF in PySpark since Spark 2.3
> (cf [How to define and use a User-Defined Aggregate Function in Spark
> SQL?|https://stackoverflow.com/questions/32100973/how-to-define-and-use-a-user-defined-aggregate-function-in-spark-sql]),
> by calling {{pandas_udf}} with the {{PandasUDFType.GROUPED_AGG}} keyword.
> However given that it is just taking a function as a parameter I don't think
> it is possible to carry state around during the aggregation with this
> function.
> From Scala, I see it is possible to have stateful aggregation by either
> extending {{UserDefinedAggregateFunction}} or
> {{org.apache.spark.sql.expressions.Aggregator}} , but is there a similar
> thing I can do on python-side only?
> If no, is this planned in a future release?
> thanks!
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