Github user freeman-lab commented on a diff in the pull request:
https://github.com/apache/spark/pull/2906#discussion_r22632512
--- Diff:
mllib/src/main/scala/org/apache/spark/mllib/clustering/HierarchicalClustering.scala
---
@@ -0,0 +1,627 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.mllib.clustering
+
+import breeze.linalg.{DenseVector => BDV, SparseVector => BSV, Vector =>
BV, norm => breezeNorm}
+import org.apache.spark.Logging
+import org.apache.spark.SparkContext._
+import org.apache.spark.mllib.linalg.{Vector, Vectors}
+import org.apache.spark.rdd.RDD
+import org.apache.spark.util.random.XORShiftRandom
+
+/**
+ * This trait is used for the configuration of the hierarchical clustering
+ */
+sealed
+trait HierarchicalClusteringConf extends Serializable {
+ this: HierarchicalClustering =>
+
+ def setNumClusters(numClusters: Int): this.type = {
+ this.numClusters = numClusters
+ this
+ }
+
+ def getNumClusters(): Int = this.numClusters
+
+ def setNumRetries(numRetries: Int): this.type = {
+ this.numRetries = numRetries
+ this
+ }
+
+ def getNumRetries(): Int = this.numRetries
+
+ def setSubIterations(subIterations: Int): this.type = {
+ this.subIterations = subIterations
+ this
+ }
+
+ def getSubIterations(): Int = this.subIterations
+
+ def setEpsilon(epsilon: Double): this.type = {
+ this.epsilon = epsilon
+ this
+ }
+
+ def getEpsilon(): Double = this.epsilon
+
+ def setRandomSeed(seed: Int): this.type = {
+ this.randomSeed = seed
+ this
+ }
+
+ def getRandomSeed(): Int = this.randomSeed
+
+ def setRandomRange(range: Double): this.type = {
+ this.randomRange = range
+ this
+ }
+}
+
+
+/**
+ * This is a divisive hierarchical clustering algorithm based on bi-sect
k-means algorithm.
+ *
+ * The main idea of this algorithm is derived from:
+ * "A comparison of document clustering techniques",
+ * M. Steinbach, G. Karypis and V. Kumar. Workshop on Text Mining, KDD,
2000.
+ * http://cs.fit.edu/~pkc/classes/ml-internet/papers/steinbach00tr.pdf
+ *
+ * @param numClusters the number of clusters you want
+ * @param subIterations the number of iterations at digging
+ * @param epsilon the threshold to stop the sub-iterations
+ * @param randomSeed uses in sampling data for initializing centers in
each sub iterations
+ * @param randomRange the range coefficient to generate random points in
each clustering step
+ */
+class HierarchicalClustering(
+ private[mllib] var numClusters: Int,
+ private[mllib] var subIterations: Int,
+ private[mllib] var numRetries: Int,
+ private[mllib] var epsilon: Double,
+ private[mllib] var randomSeed: Int,
+ private[mllib] var randomRange: Double)
+ extends Serializable with Logging with HierarchicalClusteringConf {
+
+ /**
+ * Constructs with the default configuration
+ */
+ def this() = this(20, 20, 10, 10E-4, 1, 0.1)
+
+ /** Shows the parameters */
+ override def toString(): String = {
+ Array(
+ s"numClusters:${numClusters}",
+ s"subIterations:${subIterations}",
+ s"numRetries:${numRetries}",
+ s"epsilon:${epsilon}",
+ s"randomSeed:${randomSeed}",
+ s"randomRange:${randomRange}"
+ ).mkString(", ")
+ }
+
+ /**
+ * Trains a hierarchical clustering model with the given configuration
+ *
+ * @param data training points
+ * @return a model for hierarchical clustering
+ */
+ def run(data: RDD[Vector]): HierarchicalClusteringModel = {
+ validateData(data)
+ logInfo(s"Run with ${this}")
+
+ val startTime = System.currentTimeMillis() // to measure the execution
time
+ val clusterTree = ClusterTree.fromRDD(data) // make the root node
+ val model = new HierarchicalClusteringModel(clusterTree)
+ val statsUpdater = new ClusterTreeStatsUpdater()
+
+ var node: Option[ClusterTree] = Some(model.clusterTree)
+ statsUpdater(node.get)
+
+ // If the followed conditions are satisfied, and then stop the
training.
+ // 1. There is no splittable cluster
+ // 2. The number of the splitted clusters is greater than that of
given clusters
+ var totalVariance = Double.MaxValue
+ var newTotalVariance = model.clusterTree.getVariance().get
+ var step = 1
+ while (node != None
+ && model.clusterTree.getTreeSize() < this.numClusters) {
+
+ // split some times in order not to be wrong clustering result
+ var isMerged = false
+ for (i <- 1 to this.numRetries) {
+ if (node.get.getVariance().get > this.epsilon && isMerged ==
false) {
+ var subNodes = split(node.get).map(subNode =>
statsUpdater(subNode))
+ if (subNodes.size == 2) {
+ // insert the nodes to the tree
+ node.get.insert(subNodes.toList)
+ // calculate the local dendrogram height
+ val dist = breezeNorm(subNodes(0).center.toBreeze -
subNodes(1).center.toBreeze, 2)
+ node.get.height = Some(dist)
+ // unpersist unnecessary cache because its children nodes are
cached
+ node.get.data.unpersist()
+ logInfo(s"the number of cluster is
${model.clusterTree.getTreeSize()} at step ${step}")
+ isMerged = true
+ }
+ }
+ }
+ node.get.isVisited = true
+
+ // update the total variance and select the next splittable node
+ node = nextNode(model.clusterTree)
+ step += 1
+ }
+
+ model.isTrained = true
+ val trainTime = (System.currentTimeMillis() - startTime).toInt
+ logInfo(s"Elapsed Time for Training: ${trainTime.toDouble / 1000}
[sec]")
+ model
+ }
+
+ /**
+ * validate the given data to train
+ */
+ private def validateData(data: RDD[Vector]) {
+ require(this.numClusters <= data.count(), "# clusters must be less
than # data rows")
+ }
+
+ /**
+ * Selects the next node to split
+ */
+ private[clustering] def nextNode(clusterTree: ClusterTree):
Option[ClusterTree] = {
+ // select the max variance of clusters which are leaves of a tree
+ clusterTree.toSeq().filter(tree => tree.isSplittable() &&
!tree.isVisited) match {
+ case list if list.isEmpty => None
+ case list => Some(list.maxBy(_.getVariance()))
+ }
+ }
+
+ /**
+ * Takes the initial centers for bi-sect k-means
+ */
+ private[clustering] def takeInitCenters(centers: Vector):
Array[BV[Double]] = {
+ val random = new XORShiftRandom()
+ Array(
+ centers.toBreeze.map(elm => elm - random.nextDouble() * elm *
this.randomRange),
+ centers.toBreeze.map(elm => elm + random.nextDouble() * elm *
this.randomRange)
+ )
+ }
+
+ /**
+ * Splits the given cluster (tree) with bi-sect k-means
+ *
+ * @param clusterTree the splitted cluster
+ * @return an array of ClusterTree. its size is generally 2, but its
size can be 1
+ */
+ private def split(clusterTree: ClusterTree): Array[ClusterTree] = {
+ val startTime = System.currentTimeMillis()
+ val data = clusterTree.data
+ val sc = data.sparkContext
+ var centers = takeInitCenters(clusterTree.center)
+
+ // TODO Supports distance metrics other Euclidean distance metric
+ val metric = (bv1: BV[Double], bv2: BV[Double]) => breezeNorm(bv1 -
bv2, 2.0)
+ sc.broadcast(metric)
+
+ // If the following conditions are satisfied, the iteration is stopped
+ // 1. the relative error is less than that of configuration
+ // 2. the number of executed iteration is greater than that of
configuration
+ // 3. the number of centers is equal to one. if one means that the
cluster is not splittable
+ var numIter = 0
+ var error = Double.MaxValue
+ while (error > this.epsilon
+ && numIter < this.subIterations
+ && centers.size > 1) {
+ val startTimeOfIter = System.currentTimeMillis()
+
+ sc.broadcast(centers)
--- End diff --
This use of `sc.broadcast` has no effect because the output isn't assigned
or used. Instead, you want something like `val bcCenters =
sc.broadcast(Centers)` and then access within the `map` as `bcCenters.value`.
See
[KMeans](https://github.com/apache/spark/blob/master/mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeans.scala#L181-185)
for an example.
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