Github user mengxr commented on a diff in the pull request: https://github.com/apache/spark/pull/2595#discussion_r18235836 --- Diff: mllib/src/main/scala/org/apache/spark/mllib/tree/DecisionTree.scala --- @@ -518,30 +516,58 @@ object DecisionTree extends Serializable with Logging { agg } - // Calculate bin aggregates. - timer.start("aggregation") - val binAggregates: DTStatsAggregator = { - val initAgg = if (metadata.subsamplingFeatures) { - new DTStatsAggregatorSubsampledFeatures(metadata, treeToNodeToIndexInfo) - } else { - new DTStatsAggregatorFixedFeatures(metadata, numNodes) - } - input.treeAggregate(initAgg)(binSeqOp, DTStatsAggregator.binCombOp) - } - timer.stop("aggregation") - // Calculate best splits for all nodes in the group timer.start("chooseSplits") + // In each parition, iterate all instances and compute aggregate stats for each node, + // yield an (nodeIndex, nodeAggregateStats) pair for each node. + // After a `reduceByKey` operation, + // stats of a node will be shuffled to a particular partition and be combined together, + // then best splits for nodes are found there. + // Finally, only best Splits for nodes are collected to driver to construct decision tree. + val nodeToBestSplits: Map[Int, (Split, InformationGainStats, Predict)] = + input.mapPartitions(points => { --- End diff -- ~~~ input.mapPartitions { points => ... } ~~~
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