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Posted to user@spark.apache.org by mhussain <mu...@gmail.com> on 2018/10/16 09:10:41 UTC
Pyspark Window orderBy
Hi,
I have a dataframe which looks like
+--------+---+------+----+
|group_id| id| text|type|
+--------+---+------+----+
| 1| 1| one| a|
| 1| 1| two| t|
| 1| 2| three| a|
| 1| 2| four| t|
| 1| 5| five| a|
| 1| 6| six| t|
| 1| 7| seven| a|
| 1| 9| eight| t|
| 1| 9| nine| a|
| 1| 10| ten| t|
| 1| 11|eleven| a|
+--------+---+------+----+
If I do Window operation by partitioning it on group_id and ordering it by
id then will orderby make sure that already ordered(sorted) rows retain the
same order?
e.g.
window_spec = Window.partitionBy(df.group_id).orderBy(df.id)
df = df.withColumn("row_number", row_number().over(window_spec))
Will the result always be as bellow?
+--------+---+------+----+------+
|group_id| id| text|type|row_number|
+--------+---+------+----+------+
| 1| 1| one| a| 1|
| 1| 1| two| t| 2|
| 1| 2| three| a| 3|
| 1| 2| four| t| 4|
| 1| 5| five| a| 5|
| 1| 6| six| t| 6|
| 1| 7| seven| a| 7|
| 1| 9| eight| t| 8|
| 1| 9| nine| a| 9|
| 1| 10| ten| t| 10|
| 1| 11|eleven| a| 11|
+--------+---+------+----+------+
In the nutshell my question is, how spark Window's orderBy handles already
ordered(sorted) rows? My assumption is it is stable i.e. it doesn't change
the order of already ordered rows but I couldn't find anything related to
this in the documentation. How can I make sure that my assumption is
correct?
I am using python 3.5 and pyspark 2.3.1.
Thanks.
Muddasser
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Re: [External Sender] Pyspark Window orderBy
Posted by mhussain <mu...@gmail.com>.
Yes, I did try it and you are right it behaves the same so far. I am not sure
how its gonna behave for large data sets though. I don't see anything in the
documentation confirming this behavior.
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Re: [External Sender] Pyspark Window orderBy
Posted by Femi Anthony <ol...@capitalone.com>.
I think that’s how it should behave. Did you try it out and see ?
On Tue, Oct 16, 2018 at 5:11 AM mhussain <mu...@gmail.com> wrote:
> Hi,
>
> I have a dataframe which looks like
>
> +--------+---+------+----+
> |group_id| id| text|type|
> +--------+---+------+----+
> | 1| 1| one| a|
> | 1| 1| two| t|
> | 1| 2| three| a|
> | 1| 2| four| t|
> | 1| 5| five| a|
> | 1| 6| six| t|
> | 1| 7| seven| a|
> | 1| 9| eight| t|
> | 1| 9| nine| a|
> | 1| 10| ten| t|
> | 1| 11|eleven| a|
> +--------+---+------+----+
> If I do Window operation by partitioning it on group_id and ordering it by
> id then will orderby make sure that already ordered(sorted) rows retain the
> same order?
>
> e.g.
>
> window_spec = Window.partitionBy(df.group_id).orderBy(df.id)
> df = df.withColumn("row_number", row_number().over(window_spec))
> Will the result always be as bellow?
>
> +--------+---+------+----+------+
> |group_id| id| text|type|row_number|
> +--------+---+------+----+------+
> | 1| 1| one| a| 1|
> | 1| 1| two| t| 2|
> | 1| 2| three| a| 3|
> | 1| 2| four| t| 4|
> | 1| 5| five| a| 5|
> | 1| 6| six| t| 6|
> | 1| 7| seven| a| 7|
> | 1| 9| eight| t| 8|
> | 1| 9| nine| a| 9|
> | 1| 10| ten| t| 10|
> | 1| 11|eleven| a| 11|
> +--------+---+------+----+------+
> In the nutshell my question is, how spark Window's orderBy handles already
> ordered(sorted) rows? My assumption is it is stable i.e. it doesn't change
> the order of already ordered rows but I couldn't find anything related to
> this in the documentation. How can I make sure that my assumption is
> correct?
>
> I am using python 3.5 and pyspark 2.3.1.
>
> Thanks.
> Muddasser
>
>
>
> --
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