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https://issues.apache.org/jira/browse/SPARK-2756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14080134#comment-14080134
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Apache Spark commented on SPARK-2756:
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User 'jkbradley' has created a pull request for this issue:
https://github.com/apache/spark/pull/1673
> Decision Tree bugs
> ------------------
>
> Key: SPARK-2756
> URL: https://issues.apache.org/jira/browse/SPARK-2756
> Project: Spark
> Issue Type: Bug
> Components: MLlib
> Affects Versions: 1.0.0
> Reporter: Joseph K. Bradley
> Assignee: Joseph K. Bradley
>
> 2 bugs:
> Bug 1: Indexing is inconsistent for aggregate calculations for unordered
> features (in multiclass classification with categorical features, where the
> features had few enough values such that they could be considered unordered,
> i.e., isSpaceSufficientForAllCategoricalSplits=true).
> * updateBinForUnorderedFeature indexed agg as (node, feature, featureValue,
> binIndex), where
> ** featureValue was from arr (so it was a feature value)
> ** binIndex was in [0,…, 2^(maxFeatureValue-1)-1)
> * The rest of the code indexed agg as (node, feature, binIndex, label).
> Bug 2: calculateGainForSplit (for classification):
> * It returns dummy prediction values when either the right or left children
> had 0 weight. These are incorrect for multiclass classification.
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