[jira] [Commented] (SPARK-16207) order guarantees for DataFrames

["Chris Rogers (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-16207?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15900152#comment-15900152 ] 

Chris Rogers commented on SPARK-16207:
--------------------------------------

The lack of documentation on this is immensely confusing.

> order guarantees for DataFrames
> -------------------------------
>
>                 Key: SPARK-16207
>                 URL: https://issues.apache.org/jira/browse/SPARK-16207
>             Project: Spark
>          Issue Type: Documentation
>          Components: Spark Core
>    Affects Versions: 1.6.1
>            Reporter: Max Moroz
>            Priority: Minor
>
> There's no clear explanation in the documentation about what guarantees are available for the preservation of order in DataFrames. Different blogs, SO answers, and posts on course websites suggest different things. It would be good to provide clarity on this.
> Examples of questions on which I could not find clarification:
> 1) Does groupby() preserve order?
> 2) Does take() preserve order?
> 3) Is DataFrame guaranteed to have the same order of lines as the text file it was read from? (Or as the json file, etc.)



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