com.microsoft.ml.spark.stages.StratifiedRepartition.scala Maven / Gradle / Ivy
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// Copyright (C) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License. See LICENSE in project root for information.
package com.microsoft.ml.spark.stages
import com.microsoft.ml.spark.core.contracts.{HasLabelCol, Wrappable}
import org.apache.spark.RangePartitioner
import org.apache.spark.ml.Transformer
import org.apache.spark.ml.param._
import org.apache.spark.ml.param.shared.HasSeed
import org.apache.spark.ml.util._
import org.apache.spark.sql.types._
import org.apache.spark.sql.{DataFrame, Dataset}
/** Constants for StratifiedRepartition
. */
object SPConstants {
val Count = "count"
val Equal = "equal"
val Original = "original"
val Mixed = "mixed"
}
object StratifiedRepartition extends DefaultParamsReadable[DropColumns]
/** StratifiedRepartition
repartitions the DataFrame such that each label is selected in each partition.
* This may be necessary in some cases such as in LightGBM multiclass classification, where it is necessary for
* at least one instance of each label to be present on each partition.
*/
class StratifiedRepartition(val uid: String) extends Transformer with Wrappable
with DefaultParamsWritable with HasLabelCol with HasSeed {
def this() = this(Identifiable.randomUID("StratifiedRepartition"))
val mode = new Param[String](this, "mode",
"Specify equal to repartition with replacement across all labels, specify " +
"original to keep the ratios in the original dataset, or specify mixed to use a heuristic")
setDefault(mode -> SPConstants.Mixed)
def getMode: String = $(mode)
def setMode(value: String): this.type = set(mode, value)
/** @param dataset - The input dataset, to be transformed
* @return The DataFrame that results from stratified repartitioning
*/
override def transform(dataset: Dataset[_]): DataFrame = {
// Count unique values in label column
val distinctLabelCounts = dataset.select(getLabelCol).groupBy(getLabelCol).count().collect()
val labelToCount = distinctLabelCounts.map(row => (row.getInt(0), row.getLong(1)))
val labelToFraction =
getMode match {
case SPConstants.Equal => getEqualLabelCount(labelToCount, dataset)
case SPConstants.Mixed => {
val equalLabelToCount = getEqualLabelCount(labelToCount, dataset)
val normalizedRatio = equalLabelToCount.map { case (label, count) => count }.sum / labelToCount.size
labelToCount.map { case (label, count) => (label, count / normalizedRatio)}.toMap
}
case SPConstants.Original => labelToCount.map { case (label, count) => (label, 1.0) }.toMap
case _ => throw new Exception(s"Unknown mode specified to StratifiedRepartition: $getMode")
}
val labelColIndex = dataset.schema.fieldIndex(getLabelCol)
val spdata = dataset.toDF().rdd.keyBy(row => row.getInt(labelColIndex))
.sampleByKeyExact(true, labelToFraction, getSeed)
.mapPartitions(keyToRow => keyToRow.zipWithIndex.map { case ((key, row), index) => (index, row) })
val rangePartitioner = new RangePartitioner(dataset.rdd.getNumPartitions, spdata)
val rspdata = spdata.partitionBy(rangePartitioner).mapPartitions(keyToRow =>
keyToRow.map{case (key, row) => row}).persist()
dataset.sqlContext.createDataFrame(rspdata, dataset.schema)
}
private def getEqualLabelCount(labelToCount: Array[(Int, Long)], dataset: Dataset[_]): Map[Int, Double] = {
val maxLabelCount = Math.max(labelToCount.map { case (label, count) => count }.max, dataset.rdd.getNumPartitions)
labelToCount.map { case (label, count) => (label, maxLabelCount.toDouble / count) }.toMap
}
def transformSchema(schema: StructType): StructType = schema
def copy(extra: ParamMap): DropColumns = defaultCopy(extra)
}