[GitHub] [solr] spyk commented on a change in pull request #242: SOLR-15569: Split on the right subtree when node value == threshold on MultipleAdditiveTreesModel

[GitBox <gi...@apache.org>]

spyk commented on a change in pull request #242:
URL: https://github.com/apache/solr/pull/242#discussion_r683387756



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File path: solr/contrib/ltr/src/java/org/apache/solr/ltr/model/MultipleAdditiveTreesModel.java
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@@ -292,10 +291,10 @@ private static float scoreNode(float[] featureVector, RegressionTreeNode regress
         return 0f;
       }
 
-      if (featureVector[regressionTreeNode.featureIndex] <= regressionTreeNode.threshold) {
-        regressionTreeNode = regressionTreeNode.left;
-      } else {
+      if (featureVector[regressionTreeNode.featureIndex] >= regressionTreeNode.threshold) {

Review comment:
       We run into case with a specific XGBoost model where a variable might take on 0 or 1 and the split condition being `1.0`. So, in that case if we go left by default the right path is never evaluated, which results in silently decreased model performance. 
   
   But, agree it's a rather big change, there might be issues with a) other tree models that split to the left b) backwards incompatibility, so @cpoerschke suggestion makes a lot of sense.




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