SVD++ demo

graph/src/main/scala/org/apache/spark/graph/algorithms/Svdpp.scala

@@ -0,0 +1,143 @@
+package org.apache.spark.graph.algorithms
+
+import org.apache.spark._
+import org.apache.spark.graph._
+import scala.util.Random
+import org.apache.commons.math.linear._
+
+class VD (
+  var v1: RealVector, // v1: p for user node, q for item node
+  var v2: RealVector, // v2: pu + |N(u)|^(-0.5)*sum(y) for user node, y for item node
+  var bias: Double,
+  var norm: Double // only for user node
+) extends Serializable
+
+class Msg (
+  var v1: RealVector,
+  var v2: RealVector,
+  var bias: Double
+) extends Serializable
+
+object Svdpp {
+  // implement SVD++ based on http://public.research.att.com/~volinsky/netflix/kdd08koren.pdf
+
+  def run(sc: SparkContext, input: String): Graph[VD,Double] = {
+    // defalut parameters
+    val rank = 4
+    val maxIters = 15
+    val minVal = 0.0
+    val maxVal = 5.0
+    val gamma1 = 0.007
+    val gamma2 = 0.007
+    val gamma6 = 0.005
+    val gamma7 = 0.015
+	
+    def defaultF(rank: Int) = {
+      val p = new ArrayRealVector(rank)
+      val w = new ArrayRealVector(rank)
+      for (i <- 0 until rank) {
+        p.setEntry(i, Random.nextDouble)
+        w.setEntry(i, Random.nextDouble)
+      }
+      var vd = new VD(p, w, 0.0, 0.0)
+      vd
+    }
+
+    // calculate initial norm and bias
+    def mapF0(et: EdgeTriplet[VD, Double]): Iterator[(Vid, (Long, Double))] = {
+      assert(et.srcAttr != null && et.dstAttr != null)
+      Iterator((et.srcId, (1L, et.attr)), (et.dstId, (1L, et.attr)))
+    }
+    def reduceF0(g1: (Long, Double), g2: (Long, Double)) = {
+      (g1._1 + g2._1, g1._2 + g2._2)
+    }
+    def updateF0(vid: Vid, vd: VD, msg: Option[(Long, Double)]) = {
+      if (msg.isDefined) {
+        vd.bias = msg.get._2 / msg.get._1
+        vd.norm = 1.0 / scala.math.sqrt(msg.get._1)
+      }
+      vd
+    }
+	
+    // read textfile
+    val edges = sc.textFile(input).map { line => 
+      val fields = line.split(",")
+      Edge(fields(0).toLong * 2, fields(1).toLong * 2 + 1, fields(2).toDouble)
+    }
+
+    // calculate global rating mean
+    val (rs, rc) = edges.map(e => (e.attr, 1L)).reduce((a, b) => (a._1 + b._1, a._2 + b._2))
+    val u = rs / rc // global rating mean
+
+    // make graph
+    var g = Graph.fromEdges(edges, defaultF(rank), RandomVertexCut).cache()
+
+    // calculate initial norm and bias
+    val t0 = g.mapReduceTriplets(mapF0, reduceF0)
+    g.outerJoinVertices(t0) {updateF0} 
+	
+    // phase 1
+    def mapF1(et: EdgeTriplet[VD, Double]): Iterator[(Vid, RealVector)] = {
+      assert(et.srcAttr != null && et.dstAttr != null)
+      Iterator((et.srcId, et.dstAttr.v2)) // sum up y of connected item nodes
+    }	
+    def reduceF1(g1: RealVector, g2: RealVector) = {
+      g1.add(g2)
+    }
+    def updateF1(vid: Vid, vd: VD, msg: Option[RealVector]) = {
+      if (msg.isDefined) {
+        vd.v2 = vd.v1.add(msg.get.mapMultiply(vd.norm)) // pu + |N(u)|^(-0.5)*sum(y)
+      }
+      vd
+    }
+
+    // phase 2
+    def mapF2(et: EdgeTriplet[VD, Double]): Iterator[(Vid, Msg)] = {
+      assert(et.srcAttr != null && et.dstAttr != null)
+      val usr = et.srcAttr
+      val itm = et.dstAttr
+      var p = usr.v1
+      var q = itm.v1
+      val itmBias = 0.0
+      val usrBias = 0.0
+      var pred = u + usr.bias + itm.bias + q.dotProduct(usr.v2)
+      if (pred < minVal) {
+        pred = minVal
+      }
+      if (pred > maxVal) {
+        pred = maxVal
+      }
+      val err = et.attr - pred
+      val y = (q.mapMultiply(err*usr.norm)).subtract((usr.v2).mapMultiply(gamma7))
+      val newP = (q.mapMultiply(err)).subtract(p.mapMultiply(gamma7)) // for each connected item q
+      val newQ = (usr.v2.mapMultiply(err)).subtract(q.mapMultiply(gamma7))
+      Iterator((et.srcId, new Msg(newP, y, err - gamma6*usr.bias)), (et.dstId, new Msg(newQ, y, err - gamma6*itm.bias)))
+    }	
+    def reduceF2(g1: Msg, g2: Msg):Msg = {
+      g1.v1 = g1.v1.add(g2.v1)
+      g1.v2 = g1.v2.add(g2.v2)
+      g1.bias += g2.bias
+      g1
+    }
+    def updateF2(vid: Vid, vd: VD, msg: Option[Msg]) = {
+      if (msg.isDefined) {
+        vd.v1 = vd.v1.add(msg.get.v1.mapMultiply(gamma2))
+        if (vid % 2 == 1) { // item node update y
+          vd.v2 = vd.v2.add(msg.get.v2.mapMultiply(gamma2))
+        }
+        vd.bias += msg.get.bias*gamma1
+      }
+      vd
+    }
+
+    for (i <- 0 until maxIters) {
+      // phase 1
+      val t1: VertexRDD[RealVector] = g.mapReduceTriplets(mapF1, reduceF1)
+      g.outerJoinVertices(t1) {updateF1}  
+      // phase 2
+      val t2: VertexRDD[Msg] = g.mapReduceTriplets(mapF2, reduceF2)
+      g.outerJoinVertices(t2) {updateF2}
+    }
+  g
+  }
+}