[SPARK-29967][ML][PYTHON] KMeans support instance weighting

mllib/src/main/scala/org/apache/spark/ml/clustering/KMeans.scala

@@ -31,17 +31,18 @@ import org.apache.spark.ml.util.Instrumentation.instrumented
 import org.apache.spark.mllib.clustering.{DistanceMeasure, KMeans => MLlibKMeans, KMeansModel => MLlibKMeansModel}
 import org.apache.spark.mllib.linalg.{Vector => OldVector, Vectors => OldVectors}
 import org.apache.spark.mllib.linalg.VectorImplicits._
-import org.apache.spark.sql.{DataFrame, Dataset, SparkSession}
-import org.apache.spark.sql.functions.udf
-import org.apache.spark.sql.types.{IntegerType, StructType}
+import org.apache.spark.rdd.RDD
+import org.apache.spark.sql.{DataFrame, Dataset, Row, SparkSession}
+import org.apache.spark.sql.functions._
+import org.apache.spark.sql.types.{DoubleType, IntegerType, StructType}
 import org.apache.spark.storage.StorageLevel
 import org.apache.spark.util.VersionUtils.majorVersion
 
 /**
  * Common params for KMeans and KMeansModel
  */
 private[clustering] trait KMeansParams extends Params with HasMaxIter with HasFeaturesCol
-  with HasSeed with HasPredictionCol with HasTol with HasDistanceMeasure {
+  with HasSeed with HasPredictionCol with HasTol with HasDistanceMeasure with HasWeightCol {
 
   /**
    * The number of clusters to create (k). Must be > 1. Note that it is possible for fewer than
@@ -313,12 +314,32 @@ class KMeans @Since("1.5.0") (
   @Since("1.5.0")
   def setSeed(value: Long): this.type = set(seed, value)
 
+  /**
+   * Sets the value of param [[weightCol]].
+   * If this is not set or empty, we treat all instance weights as 1.0.
+   * Default is not set, so all instances have weight one.
+   *
+   * @group setParam
+   */
+  @Since("3.0.0")
+  def setWeightCol(value: String): this.type = set(weightCol, value)
+
   @Since("2.0.0")
   override def fit(dataset: Dataset[_]): KMeansModel = instrumented { instr =>
     transformSchema(dataset.schema, logging = true)
 
     val handlePersistence = dataset.storageLevel == StorageLevel.NONE
-    val instances = DatasetUtils.columnToOldVector(dataset, getFeaturesCol)
+    val w = if (isDefined(weightCol) && $(weightCol).nonEmpty) {
+      col($(weightCol)).cast(DoubleType)
+    } else {
+      lit(1.0)
+    }
+
+    val instances: RDD[(OldVector, Double)] = dataset.select(
+      DatasetUtils.columnToVector(dataset, getFeaturesCol),
+      w).rdd.map {
+      case Row(point: Vector, weight: Double) => (OldVectors.fromML(point), weight)
+    }
 
     if (handlePersistence) {
       instances.persist(StorageLevel.MEMORY_AND_DISK)
@@ -327,7 +348,7 @@ class KMeans @Since("1.5.0") (
     instr.logPipelineStage(this)
     instr.logDataset(dataset)
     instr.logParams(this, featuresCol, predictionCol, k, initMode, initSteps, distanceMeasure,
-      maxIter, seed, tol)
+      maxIter, seed, tol, weightCol)
     val algo = new MLlibKMeans()
       .setK($(k))
       .setInitializationMode($(initMode))
@@ -336,7 +357,7 @@ class KMeans @Since("1.5.0") (
       .setSeed($(seed))
       .setEpsilon($(tol))
       .setDistanceMeasure($(distanceMeasure))
-    val parentModel = algo.run(instances, Option(instr))
+    val parentModel = algo.runWithweight(instances, Option(instr))
     val model = copyValues(new KMeansModel(uid, parentModel).setParent(this))
     val summary = new KMeansSummary(
       model.transform(dataset),

mllib/src/main/scala/org/apache/spark/mllib/clustering/DistanceMeasure.scala

@@ -84,8 +84,8 @@ private[spark] abstract class DistanceMeasure extends Serializable {
    * @param point a `VectorWithNorm` to be added to `sum` of a cluster
    * @param sum the `sum` for a cluster to be updated
    */
-  def updateClusterSum(point: VectorWithNorm, sum: Vector): Unit = {
-    axpy(1.0, point.vector, sum)
+  def updateClusterSum(point: VectorWithNorm, sum: Vector, weight: Double = 1.0): Unit = {
+    axpy(weight, point.vector, sum)
   }
 
   /**
@@ -100,6 +100,18 @@ private[spark] abstract class DistanceMeasure extends Serializable {
     new VectorWithNorm(sum)
   }
 
+  /**
+   * Returns a centroid for a cluster given its `sum` vector and the weightSum of points.
+   *
+   * @param sum   the `sum` for a cluster
+   * @param weightSum the weightSum of points in the cluster
+   * @return the centroid of the cluster
+   */
+  def centroid(sum: Vector, weightSum: Double): VectorWithNorm = {
+    scal(1.0 / weightSum, sum)
+    new VectorWithNorm(sum)
+  }
+
   /**
    * Returns two new centroids symmetric to the specified centroid applying `noise` with the
    * with the specified `level`.
@@ -249,9 +261,9 @@ private[spark] class CosineDistanceMeasure extends DistanceMeasure {
    * @param point a `VectorWithNorm` to be added to `sum` of a cluster
    * @param sum the `sum` for a cluster to be updated
    */
-  override def updateClusterSum(point: VectorWithNorm, sum: Vector): Unit = {
+  override def updateClusterSum(point: VectorWithNorm, sum: Vector, weight: Double = 1.0): Unit = {
     assert(point.norm > 0, "Cosine distance is not defined for zero-length vectors.")
-    axpy(1.0 / point.norm, point.vector, sum)
+    axpy(weight / point.norm, point.vector, sum)
   }
 
   /**

mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeans.scala

@@ -23,7 +23,7 @@ import org.apache.spark.annotation.Since
 import org.apache.spark.broadcast.Broadcast
 import org.apache.spark.internal.Logging
 import org.apache.spark.ml.util.Instrumentation
-import org.apache.spark.mllib.linalg.{Vector, Vectors}
+import org.apache.spark.mllib.linalg.{DenseVector, SparseVector, Vector, Vectors}
 import org.apache.spark.mllib.linalg.BLAS.axpy
 import org.apache.spark.rdd.RDD
 import org.apache.spark.storage.StorageLevel
@@ -209,11 +209,14 @@ class KMeans private (
    */
   @Since("0.8.0")
   def run(data: RDD[Vector]): KMeansModel = {
-    run(data, None)
+    val instances: RDD[(Vector, Double)] = data.map {
+      case (point) => (point, 1.0)
+    }
+    runWithweight(instances, None)
   }
 
-  private[spark] def run(
-      data: RDD[Vector],
+  private[spark] def runWithweight(
+      data: RDD[(Vector, Double)],
       instr: Option[Instrumentation]): KMeansModel = {
 
     if (data.getStorageLevel == StorageLevel.NONE) {
@@ -222,12 +225,15 @@ class KMeans private (
     }
 
     // Compute squared norms and cache them.
-    val norms = data.map(Vectors.norm(_, 2.0))
-    val zippedData = data.zip(norms).map { case (v, norm) =>
-      new VectorWithNorm(v, norm)
+    val norms = data.map { case (v, _) =>
+      Vectors.norm(v, 2.0)
+    }
+
+    val zippedData = data.zip(norms).map { case ((v, w), norm) =>
+      (new VectorWithNorm(v, norm), w)
     }
     zippedData.persist()
-    val model = runAlgorithm(zippedData, instr)
+    val model = runAlgorithmWithWeight(zippedData, instr)
     zippedData.unpersist()
 
     // Warn at the end of the run as well, for increased visibility.
@@ -241,8 +247,8 @@ class KMeans private (
   /**
    * Implementation of K-Means algorithm.
    */
-  private def runAlgorithm(
-      data: RDD[VectorWithNorm],
+  private def runAlgorithmWithWeight(
+      data: RDD[(VectorWithNorm, Double)],
       instr: Option[Instrumentation]): KMeansModel = {
 
     val sc = data.sparkContext
@@ -251,14 +257,17 @@ class KMeans private (
 
     val distanceMeasureInstance = DistanceMeasure.decodeFromString(this.distanceMeasure)
 
+    val dataVectorWithNorm = data.map(d => d._1)
+    val weights = data.map(d => d._2)
+
     val centers = initialModel match {
       case Some(kMeansCenters) =>
         kMeansCenters.clusterCenters.map(new VectorWithNorm(_))
       case None =>
         if (initializationMode == KMeans.RANDOM) {
-          initRandom(data)
+          initRandom(dataVectorWithNorm)
         } else {
-          initKMeansParallel(data, distanceMeasureInstance)
+          initKMeansParallel(dataVectorWithNorm, distanceMeasureInstance)
         }
     }
     val initTimeInSeconds = (System.nanoTime() - initStartTime) / 1e9
@@ -278,30 +287,32 @@ class KMeans private (
       val bcCenters = sc.broadcast(centers)
 
       // Find the new centers
-      val collected = data.mapPartitions { points =>
+      val collected = data.mapPartitions { pointsAndWeights =>
         val thisCenters = bcCenters.value
         val dims = thisCenters.head.vector.size
 
         val sums = Array.fill(thisCenters.length)(Vectors.zeros(dims))
-        val counts = Array.fill(thisCenters.length)(0L)
 
-        points.foreach { point =>
-          val (bestCenter, cost) = distanceMeasureInstance.findClosest(thisCenters, point)
+        // clusterWeightSum is needed to calculate cluster center
+        // cluster center =
+        //     sample1 * weight1/clusterWeightSum + sample2 * weight2/clusterWeightSum + ...
+        val clusterWeightSum = Array.fill(thisCenters.length)(0.0)
+
+        pointsAndWeights.foreach { case (point, weight) =>
+          var (bestCenter, cost) = distanceMeasureInstance.findClosest(thisCenters, point)
+          cost *= weight
           costAccum.add(cost)
-          distanceMeasureInstance.updateClusterSum(point, sums(bestCenter))
-          counts(bestCenter) += 1
+          distanceMeasureInstance.updateClusterSum(point, sums(bestCenter), weight)
+          clusterWeightSum(bestCenter) += weight
         }
 
-        counts.indices.filter(counts(_) > 0).map(j => (j, (sums(j), counts(j)))).iterator
-      }.reduceByKey { case ((sum1, count1), (sum2, count2)) =>
+        clusterWeightSum.indices.filter(clusterWeightSum(_) > 0)
+          .map(j => (j, (sums(j), clusterWeightSum(j)))).iterator
+      }.reduceByKey { case ((sum1, clusterWeightSum1), (sum2, clusterWeightSum2)) =>
         axpy(1.0, sum2, sum1)
-        (sum1, count1 + count2)
+        (sum1, clusterWeightSum1 + clusterWeightSum2)
       }.collectAsMap()
 
-      if (iteration == 0) {
-        instr.foreach(_.logNumExamples(collected.values.map(_._2).sum))
-      }
-
       val newCenters = collected.mapValues { case (sum, count) =>
         distanceMeasureInstance.centroid(sum, count)
       }