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https://issues.apache.org/jira/browse/SPARK-3272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14115757#comment-14115757
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Joseph K. Bradley commented on SPARK-3272:
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Hi Qiping,
No worries; we are on different time zones. I think we had different ideas
about the semantics of the min instances requirement:
(a) I was thinking of it as min_instances_to_split, i.e., a node becomes a leaf
node if fewer than K training instances apply to that node.
(b) It sounds like you are thinking of min_instances_to_be_a_leaf, i.e., if we
find the bestSplit for a node creates a left or right child with fewer than K
training instances, then the bestSplit is rejected, and the node becomes a leaf
node.
Both (a) and (b) sound useful, and it looks like scikit-learn supports both.
I'm fine with only supporting one of the two for now, so going with your
suggestion of (b) sounds good to me. For (b), I agree about storing counts of
left & right instances.
Could you please clarify the JIRA [SPARK-2207] about which of (a) or (b) you
plan to implement?
As far as the invalid info gain value, I am OK with that (since it will be
internal).
Thanks for thinking through this! ~ Joseph
> Calculate prediction for nodes separately from calculating information gain
> for splits in decision tree
> -------------------------------------------------------------------------------------------------------
>
> Key: SPARK-3272
> URL: https://issues.apache.org/jira/browse/SPARK-3272
> Project: Spark
> Issue Type: Improvement
> Components: MLlib
> Affects Versions: 1.0.2
> Reporter: Qiping Li
> Fix For: 1.1.0
>
>
> In current implementation, prediction for a node is calculated along with
> calculation of information gain stats for each possible splits. The value to
> predict for a specific node is determined, no matter what the splits are.
> To save computation, we can first calculate prediction first and then
> calculate information gain stats for each split.
> This is also necessary if we want to support minimum instances per node
> parameters([SPARK-2207|https://issues.apache.org/jira/browse/SPARK-2207])
> because when all splits don't satisfy minimum instances requirement , we
> don't use information gain of any splits. There should be a way to get the
> prediction value.
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