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https://issues.apache.org/jira/browse/MAHOUT-945?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13187883#comment-13187883
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Ikumasa Mukai commented on MAHOUT-945:
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Hi wang-san.
Thank you for your detailed explanation.
It is the point that we must use the weighted average, right?
If I stick to use the total values for calc on your example,
the 1st split should be calced like 25.63-(16.6*11+19*1.1) and
the 2nd split should be 25.63-(1.67*11+37.5*1.1).
Could I catch your suggestion?
> The variance calculation of Random forest regression tree
> ---------------------------------------------------------
>
> Key: MAHOUT-945
> URL: https://issues.apache.org/jira/browse/MAHOUT-945
> Project: Mahout
> Issue Type: Improvement
> Components: Classification
> Affects Versions: 0.6
> Reporter: Wang Yue
> Labels: Regressionsplit.java
> Attachments: MAHOUT-945.patch
>
> Original Estimate: 48h
> Remaining Estimate: 48h
>
> Hi, Mukai
> Thanks for your efforts in expand the RF to regression. However, I have a
> doubt about your implementation regarding to Regressionsplit.java. The
> variance method
> "
> private static double variance(double[] s, double[] ss, double[] dataSize) {
> double var = 0;
> for (int i = 0; i < s.length; i++) {
> if (dataSize[i] > 0) {
> var += ss[i] - ((s[i] * s[i]) / dataSize[i]);
> }
> }
> return var;
> }
> "
> While the variance in my mind should be something like
> var += ss[i]/dataSize[i] - ((s[i] * s[i]) / (dataSize[i]*dataSize[i]));
> Please help correct me if I am wrong. Thanks
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