Github user chouqin commented on a diff in the pull request:
https://github.com/apache/spark/pull/2435#discussion_r17764228
--- Diff:
mllib/src/main/scala/org/apache/spark/mllib/tree/impl/DTStatsAggregator.scala
---
@@ -189,6 +160,230 @@ private[tree] class DTStatsAggregator(
}
this
}
+}
+
+/**
+ * DecisionTree statistics aggregator.
+ * This holds a flat array of statistics for a set of (nodes, features,
bins)
+ * and helps with indexing.
+ *
+ * This instance of [[DTStatsAggregator]] is used when not subsampling
features.
+ *
+ * @param numNodes Number of nodes to collect statistics for.
+ */
+private[tree] class DTStatsAggregatorFixedFeatures(
+ metadata: DecisionTreeMetadata,
+ numNodes: Int) extends DTStatsAggregator(metadata) {
+
+ /**
+ * Offset for each feature for calculating indices into the
[[_allStats]] array.
+ * Mapping: featureIndex --> offset
+ */
+ private val featureOffsets: Array[Int] = {
+ metadata.numBins.scanLeft(0)((total, nBins) => total + statsSize *
nBins)
+ }
+
+ /**
+ * Number of elements for each node, corresponding to stride between
nodes in [[_allStats]].
+ */
+ private val nodeStride: Int = featureOffsets.last
+
+ /**
+ * Total number of elements stored in this aggregator.
+ */
+ def allStatsSize: Int = numNodes * nodeStride
+
+ /**
+ * Flat array of elements.
+ * Index for start of stats for a (node, feature, bin) is:
+ * index = nodeIndex * nodeStride + featureOffsets(featureIndex) +
binIndex * statsSize
+ * Note: For unordered features, the left child stats precede the right
child stats
+ * in the binIndex order.
+ */
+ protected val _allStats: Array[Double] = new Array[Double](allStatsSize)
+
+ /**
+ * Get flat array of elements stored in this aggregator.
+ */
+ protected def allStats: Array[Double] = _allStats
+
+ /**
+ * Update the stats for a given (node, feature, bin) for ordered
features, using the given label.
+ */
+ def update(
+ nodeIndex: Int,
+ featureIndex: Int,
+ binIndex: Int,
+ label: Double,
+ instanceWeight: Double): Unit = {
+ val i = nodeIndex * nodeStride + featureOffsets(featureIndex) +
binIndex * statsSize
+ impurityAggregator.update(_allStats, i, label, instanceWeight)
+ }
+
+ /**
+ * Pre-compute node offset for use with [[nodeUpdate]].
+ */
+ def getNodeOffset(nodeIndex: Int): Int = nodeIndex * nodeStride
+
+ /**
+ * Faster version of [[update]].
+ * Update the stats for a given (node, feature, bin) for ordered
features, using the given label.
+ * @param nodeOffset Pre-computed node offset from [[getNodeOffset]].
+ */
+ def nodeUpdate(
+ nodeOffset: Int,
+ nodeIndex: Int,
--- End diff --
sorry, `nodeIndex` is needed in `DTStatsAggregatorSubsampledFeatures`.
Close this comment.
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