zhengruifeng opened a new pull request #27070: [SPARK-9612][ML][FOLLOWUP] fix GBT support weights if subsamplingRate<1 URL: https://github.com/apache/spark/pull/27070 ### What changes were proposed in this pull request? fix `BaggedPoint.convertToBaggedRDD` when `subsamplingRate < 1.0` ### Why are the changes needed? 1, `baggedPoint: BaggedPoint[TreePoint]` is used in the tree growth to find best split; 2, `BaggedPoint[TreePoint]` contains two weights: ```scala class BaggedPoint[Datum](val datum: Datum, val subsampleCounts: Array[Int], val sampleWeight: Double = 1.0) class TreePoint(val label: Double, val binnedFeatures: Array[Int], val weight: Double) ``` 3, only the var `sampleWeight` in `BaggedPoint` is used, the var `weight` in `TreePoint` is never used in finding splits; 4, The method `BaggedPoint.convertToBaggedRDD` was changed in https://github.com/apache/spark/pull/21632, it was only for decisiontree, so only the following code path was changed; ``` if (numSubsamples == 1 && subsamplingRate == 1.0) { convertToBaggedRDDWithoutSampling(input, extractSampleWeight) } ``` 5, In https://github.com/apache/spark/pull/25926, I made GBT support weights, but only test it with default `subsamplingRate==1`. GBT with `subsamplingRate<1` will convert treePoints to baggedPoints via ```scala convertToBaggedRDDSamplingWithoutReplacement(input, subsamplingRate, numSubsamples, seed) ``` in which the orignial weights from `weightCol` will be discarded and all `sampleWeight` are assigned default 1.0; ### Does this PR introduce any user-facing change? No ### How was this patch tested? updated testsuites
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