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https://issues.apache.org/jira/browse/SPARK-5436?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14321028#comment-14321028
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Chris T commented on SPARK-5436:
--------------------------------

What we normally observe is that the error rate assessed against the test data 
decreases initially, and then starts to increase as the model begins to 
overfit. I think the first step would be to just store/return the error on each 
boosting iteration. After the model building is complete, this error rate can 
be examined, and a submodel extracted based on where the error in minimum. I 
don't think the level of error at the minimum can be known a priori.

> Validate GradientBoostedTrees during training
> ---------------------------------------------
>
>                 Key: SPARK-5436
>                 URL: https://issues.apache.org/jira/browse/SPARK-5436
>             Project: Spark
>          Issue Type: Improvement
>          Components: MLlib
>    Affects Versions: 1.3.0
>            Reporter: Joseph K. Bradley
>
> For Gradient Boosting, it would be valuable to compute test error on a 
> separate validation set during training.  That way, training could stop early 
> based on the test error (or some other metric specified by the user).



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