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https://issues.apache.org/jira/browse/SPARK-8971?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xiangrui Meng updated SPARK-8971:
---------------------------------
    Assignee: Seth Hendrickson

> Support balanced class labels when splitting train/cross validation sets
> ------------------------------------------------------------------------
>
>                 Key: SPARK-8971
>                 URL: https://issues.apache.org/jira/browse/SPARK-8971
>             Project: Spark
>          Issue Type: New Feature
>          Components: ML
>            Reporter: Feynman Liang
>            Assignee: Seth Hendrickson
>
> {{CrossValidator}} and the proposed {{TrainValidatorSplit}} (SPARK-8484) are 
> Spark classes which partition data into training and evaluation sets for 
> performing hyperparameter selection via cross validation.
> Both methods currently perform the split by randomly sampling the datasets. 
> However, when class probabilities are highly imbalanced (e.g. detection of 
> extremely low-frequency events), random sampling may result in cross 
> validation sets not representative of actual out-of-training performance 
> (e.g. no positive training examples could be included).
> Mainstream R packages like already 
> [caret|http://topepo.github.io/caret/splitting.html] support splitting the 
> data based upon the class labels.



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