[jira] [Updated] (SPARK-19428) Ability to select first row of groupby

["Koert Kuipers (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-19428?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Koert Kuipers updated SPARK-19428:
----------------------------------

if I remember correctly window function is like a canned secondary sort
with limited functionality, meaning this gets all pushed to the reducer. so
that is great for selecting a large number but somewhat inefficient for
taking say first 10 (compared to aggregator)

On Feb 5, 2017 11:47, "Herman van Hovell (JIRA)" <ji...@apache.org> wrote:


    [ https://issues.apache.org/jira/browse/SPARK-19428?page=
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Herman van Hovell commented on SPARK-19428:
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You could also use a window function:
{noformat}
import org.apache.spark.sql.expressions.Window
val df = spark.range(10000).select($"id" % 100 as "a", $"id" as "b")
df.withColumn("rn",
row_number().over(Window.partitionBy($"a").orderBy($"b"))).filter($"rn"
< 10)
{noformat}

Pandas has something like this:



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> Ability to select first row of groupby
> --------------------------------------
>
>                 Key: SPARK-19428
>                 URL: https://issues.apache.org/jira/browse/SPARK-19428
>             Project: Spark
>          Issue Type: Brainstorming
>          Components: SQL
>    Affects Versions: 2.1.0
>            Reporter: Luke Miner
>            Priority: Minor
>
> It would be nice to be able to select the first row from {{GroupedData}}. Pandas has something like this:
> {{df.groupby('group').first()}}
> It's especially handy if you can order the group as well.



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