+1 On Thu, Nov 7, 2019 at 6:54 PM Shane Knapp <skn...@berkeley.edu> wrote:
> +1 > > On Thu, Nov 7, 2019 at 6:08 PM Hyukjin Kwon <gurwls...@gmail.com> wrote: > > > > +1 > > > > 2019년 11월 6일 (수) 오후 11:38, Wenchen Fan <cloud0...@gmail.com>님이 작성: > >> > >> Sounds reasonable to me. We should make the behavior consistent within > Spark. > >> > >> On Tue, Nov 5, 2019 at 6:29 AM Bryan Cutler <cutl...@gmail.com> wrote: > >>> > >>> Currently, when a PySpark Row is created with keyword arguments, the > fields are sorted alphabetically. This has created a lot of confusion with > users because it is not obvious (although it is stated in the pydocs) that > they will be sorted alphabetically. Then later when applying a schema and > the field order does not match, an error will occur. Here is a list of some > of the JIRAs that I have been tracking all related to this issue: > SPARK-24915, SPARK-22232, SPARK-27939, SPARK-27712, and relevant discussion > of the issue [1]. > >>> > >>> The original reason for sorting fields is because kwargs in python < > 3.6 are not guaranteed to be in the same order that they were entered [2]. > Sorting alphabetically ensures a consistent order. Matters are further > complicated with the flag _from_dict_ that allows the Row fields to to be > referenced by name when made by kwargs, but this flag is not serialized > with the Row and leads to inconsistent behavior. For instance: > >>> > >>> >>> spark.createDataFrame([Row(A="1", B="2")], "B string, A > string").first() > >>> Row(B='2', A='1') > >>> >>> spark.createDataFrame(spark.sparkContext.parallelize([Row(A="1", > B="2")]), "B string, A string").first() > >>> Row(B='1', A='2') > >>> > >>> I think the best way to fix this is to remove the sorting of fields > when constructing a Row. For users with Python 3.6+, nothing would change > because these versions of Python ensure that the kwargs stays in the > ordered entered. For users with Python < 3.6, using kwargs would check a > conf to either raise an error or fallback to a LegacyRow that sorts the > fields as before. With Python < 3.6 being deprecated now, this LegacyRow > can also be removed at the same time. There are also other ways to create > Rows that will not be affected. I have opened a JIRA [3] to capture this, > but I am wondering what others think about fixing this for Spark 3.0? > >>> > >>> [1] https://github.com/apache/spark/pull/20280 > >>> [2] https://www.python.org/dev/peps/pep-0468/ > >>> [3] https://issues.apache.org/jira/browse/SPARK-29748 > > > > -- > Shane Knapp > UC Berkeley EECS Research / RISELab Staff Technical Lead > https://rise.cs.berkeley.edu > > --------------------------------------------------------------------- > To unsubscribe e-mail: user-unsubscr...@spark.apache.org > > -- Takuya UESHIN Tokyo, Japan http://twitter.com/ueshin
