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https://issues.apache.org/jira/browse/SPARK-16207?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15900220#comment-15900220
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Chris Rogers commented on SPARK-16207:
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[~srowen] since there is no documentation yet, I don't know whether a clear,
coherent generalization can be made. I would be happy with "most of the
methods DO NOT preserve order, with these specific exceptions", or "most of the
methods DO preserve order, with these specific exceptions".
Failing a generalization, I'd also be happy with method-by-method documentation
of ordering semantics, which seems like a very minimal amount of copy-pasting
("Preserves ordering: yes", "Preserves ordering: no"). Maybe that's a good
place to start, since there seems to be some confusion about what the
generalization would be.
> 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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