ensuring num bins is always greater than max number of categories

Author: manishamde

mllib/src/main/scala/org/apache/spark/mllib/tree/DecisionTree.scala

@@ -816,7 +816,15 @@ object DecisionTree extends Serializable with Logging {
 
     val maxBins = strategy.maxBins
     val numBins = if (maxBins <= count) maxBins else count.toInt
-    logDebug("maxBins = " + numBins)
+    logDebug("numBins = " + numBins)
+
+    // I will also add a require statement ensuring #bins is always greater than the categories
+    // It's a limitation of the current implementation but a reasonable tradeoff since features
+    // with large number of categories get favored over continuous features.
+    if (strategy.categoricalFeaturesInfo.size > 0){
+      val maxCategoriesForFeatures = strategy.categoricalFeaturesInfo.maxBy(_._2)._2
+      require(numBins >= maxCategoriesForFeatures)
+    }
 
     // Calculate the number of sample for approximate quantile calculation
     val requiredSamples = numBins*numBins