[jira] [Resolved] (SPARK-9075) DecisionTreeMetadata - setting maxPossibleBins to numExamples is incorrect.

["Joseph K. Bradley (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-9075?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Joseph K. Bradley resolved SPARK-9075.
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    Resolution: Not A Problem

> DecisionTreeMetadata - setting maxPossibleBins to numExamples is incorrect. 
> ----------------------------------------------------------------------------
>
>                 Key: SPARK-9075
>                 URL: https://issues.apache.org/jira/browse/SPARK-9075
>             Project: Spark
>          Issue Type: Bug
>          Components: MLlib
>    Affects Versions: 1.4.0
>            Reporter: Les Selecky
>            Priority: Minor
>
> In https://github.com/apache/spark/blob/master/mllib/src/main/scala/org/apache/spark/mllib/tree/impl/DecisionTreeMetadata.scala there's a statement that sets maxPossibileBins to numExamples when numExamples is less than strategy.maxBins. 
> This can cause an error when training small partitions; the error is triggered further down in the logic where it's required that maxCategoriesPerFeature be less than or equal to maxPossibleBins.
> Here's the an example of how it was manifested: the partition contained 49 rows (i.e., numExamples=49 but strategy.maxBins was 57.
> The maxPossibleBins = math.min(strategy.maxBins, numExamples) logic therefore reduced maxPossibleBins to 49 causing the "require(maxCategoriesPerFeature <= maxPossibleBins" to throw an error.
> In short, this will be a problem when training small datasets with a feature that contains more categories than numExamples.
> In our local testing we commented out the "math.min(strategy.maxBins, numExamples)" line and the decision tree succeeded where it had failed previously.



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