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https://issues.apache.org/jira/browse/SPARK-23929?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16453646#comment-16453646
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Hyukjin Kwon commented on SPARK-23929:
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How about we document the current behaviour for now and then we start a
discussion in mailing list when we are close to 3.0.0? I think we already
started to talk about Spark 3.0.0.
So, we fix the documentation first here (for 2.4.0 maybe) and it'd be good to
start the discussion about this again when we are clear on 3.0.0.
> pandas_udf schema mapped by position and not by name
> ----------------------------------------------------
>
> Key: SPARK-23929
> URL: https://issues.apache.org/jira/browse/SPARK-23929
> Project: Spark
> Issue Type: Bug
> Components: PySpark
> Affects Versions: 2.3.0
> Environment: PySpark
> Spark 2.3.0
>
> Reporter: Omri
> Priority: Major
>
> The return struct of a pandas_udf should be mapped to the provided schema by
> name. Currently it's not the case.
> Consider these two examples, where the only change is the order of the fields
> in the provided schema struct:
> {code:java}
> from pyspark.sql.functions import pandas_udf, PandasUDFType
> df = spark.createDataFrame(
> [(1, 1.0), (1, 2.0), (2, 3.0), (2, 5.0), (2, 10.0)],
> ("id", "v"))
> @pandas_udf("v double,id long", PandasUDFType.GROUPED_MAP)
> def normalize(pdf):
> v = pdf.v
> return pdf.assign(v=(v - v.mean()) / v.std())
> df.groupby("id").apply(normalize).show()
> {code}
> and this one:
> {code:java}
> from pyspark.sql.functions import pandas_udf, PandasUDFType
> df = spark.createDataFrame(
> [(1, 1.0), (1, 2.0), (2, 3.0), (2, 5.0), (2, 10.0)],
> ("id", "v"))
> @pandas_udf("id long,v double", PandasUDFType.GROUPED_MAP)
> def normalize(pdf):
> v = pdf.v
> return pdf.assign(v=(v - v.mean()) / v.std())
> df.groupby("id").apply(normalize).show()
> {code}
> The results should be the same but they are different:
> For the first code:
> {code:java}
> +---+---+
> | v| id|
> +---+---+
> |1.0| 0|
> |1.0| 0|
> |2.0| 0|
> |2.0| 0|
> |2.0| 1|
> +---+---+
> {code}
> For the second code:
> {code:java}
> +---+-------------------+
> | id| v|
> +---+-------------------+
> | 1|-0.7071067811865475|
> | 1| 0.7071067811865475|
> | 2|-0.8320502943378437|
> | 2|-0.2773500981126146|
> | 2| 1.1094003924504583|
> +---+-------------------+
> {code}
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