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https://issues.apache.org/jira/browse/SPARK-20265?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15961771#comment-15961771
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Apache Spark commented on SPARK-20265:
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User 'Syrux' has created a pull request for this issue:
https://github.com/apache/spark/pull/17575
> Improve Prefix'span pre-processing efficiency
> ---------------------------------------------
>
> Key: SPARK-20265
> URL: https://issues.apache.org/jira/browse/SPARK-20265
> Project: Spark
> Issue Type: Improvement
> Components: MLlib
> Affects Versions: 2.1.0
> Reporter: Cyril de Vogelaere
> Priority: Minor
> Original Estimate: 0h
> Remaining Estimate: 0h
>
> Given the sequence :
> 0 4 0 1 0 2 0 5 0 2 0 4 0 5
> And supposing only item 4 and 5 are frequent. The current implementation will
> clean the sequence as follow.
> 0 4 0 0 0 5 0 0 4 0 5
> Which, while still giving the same results, inneficiently leave sequences of
> zero. A quick change in the code can removes those sequence of zeros, while
> not changing the returned solutions.
> I ran test to mesure efficiency gain, they are available in the graph below :
> https://postimg.org/image/9x6ireuvn/
> As you can see, the performance increase is signifiant.
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