Github user smurching commented on a diff in the pull request: https://github.com/apache/spark/pull/19666#discussion_r149238185 --- Diff: mllib/src/main/scala/org/apache/spark/ml/tree/impl/RandomForest.scala --- @@ -741,17 +678,43 @@ private[spark] object RandomForest extends Logging { (splits(featureIndex)(bestFeatureSplitIndex), bestFeatureGainStats) } else if (binAggregates.metadata.isUnordered(featureIndex)) { // Unordered categorical feature - val leftChildOffset = binAggregates.getFeatureOffset(featureIndexIdx) - val (bestFeatureSplitIndex, bestFeatureGainStats) = - Range(0, numSplits).map { splitIndex => - val leftChildStats = binAggregates.getImpurityCalculator(leftChildOffset, splitIndex) - val rightChildStats = binAggregates.getParentImpurityCalculator() - .subtract(leftChildStats) + val numBins = binAggregates.metadata.numBins(featureIndex) + val featureOffset = binAggregates.getFeatureOffset(featureIndexIdx) + + val binStatsArray = Array.tabulate(numBins) { binIndex => + binAggregates.getImpurityCalculator(featureOffset, binIndex) + } + val parentStats = binAggregates.getParentImpurityCalculator() + + var bestGain = Double.NegativeInfinity + var bestSet: BitSet = null + var bestLeftChildStats: ImpurityCalculator = null + var bestRightChildStats: ImpurityCalculator = null + + traverseUnorderedSplits[ImpurityCalculator](numBins, null, --- End diff -- Could you please add a comment explaining what this does? E.g.: `// Computes the best split for the current feature, storing the result across the vars above`
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