imatiach-msft commented on a change in pull request #21632:
[SPARK-19591][ML][MLlib] Add sample weights to decision trees
URL: https://github.com/apache/spark/pull/21632#discussion_r245549304
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File path: mllib/src/main/scala/org/apache/spark/ml/tree/impl/BaggedPoint.scala
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@@ -33,13 +33,20 @@ import org.apache.spark.util.random.XORShiftRandom
* this datum has 1 copy, 0 copies, and 4 copies in the 3 subsamples,
respectively.
*
* @param datum Data instance
- * @param subsampleWeights Weight of this instance in each subsampled dataset.
- *
- * TODO: This does not currently support (Double) weighted instances. Once
MLlib has weighted
- * dataset support, update. (We store subsampleWeights as Double for
this future extension.)
+ * @param subsampleCounts Number of samples of this instance in each
subsampled dataset.
+ * @param sampleWeight The weight of this instance.
*/
-private[spark] class BaggedPoint[Datum](val datum: Datum, val
subsampleWeights: Array[Double])
- extends Serializable
+private[spark] class BaggedPoint[Datum](
+ val datum: Datum,
+ val subsampleCounts: Array[Int],
+ val sampleWeight: Double) extends Serializable {
+
+ /**
+ * Subsample counts weighted by the sample weight.
+ */
+ def weightedCounts: Array[Double] = subsampleCounts.map(_ * sampleWeight)
Review comment:
I was going to say I'm not sure as well - as you said there is a small trade
off - also I would mention that for clarity in code I think it is a bit clearer
what the field is this way as opposed to doing the computation beforehand.
However, I noticed this field isn't even used anywhere, it's just there for
clarity, in here:
mllib/src/main/scala/org/apache/spark/ml/tree/impl/RandomForest.scala
we get a single subsample count and weight and they are passed separately to
another method orderedBinSeqOp or mixedBinSeqOp
I guess it's nice to have this method for clarity or even debugging but if
it's not used maybe I should just get rid of it altogether to limit confusion?
What are your thoughts on this?
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