remove lazy eval, and minor memory footprint

Author: yinxusen

mllib/src/main/scala/org/apache/spark/mllib/rdd/VectorRDDFunctions.scala

@@ -53,35 +53,46 @@ private class VectorRDDStatisticsAggregator(
     val currMin: BDV[Double]) extends VectorRDDStatisticalSummary with Serializable {
 
   // lazy val is used for computing only once time. Same below.
-  override lazy val mean = Vectors.fromBreeze(currMean :* nnz :/ totalCnt)
+  override def mean = {
+    val realMean = BDV.zeros[Double](currMean.length)
+    var i = 0
+    while (i < currMean.length) {
+      realMean(i) = currMean(i) * nnz(i) / totalCnt
+      i += 1
+    }
+    Vectors.fromBreeze(realMean)
+  }
 
-  override lazy val variance = {
+  override def variance = {
+    val realVariance = BDV.zeros[Double](currM2n.length)
     val deltaMean = currMean
     var i = 0
     while (i < currM2n.size) {
-      currM2n(i) += deltaMean(i) * deltaMean(i) * nnz(i) * (totalCnt - nnz(i)) / totalCnt
-      currM2n(i) /= totalCnt
+      realVariance(i) = currM2n(i) + deltaMean(i) * deltaMean(i) * nnz(i) * (totalCnt - nnz(i)) / totalCnt
+      realVariance(i) /= totalCnt
       i += 1
     }
-    Vectors.fromBreeze(currM2n)
+    Vectors.fromBreeze(realVariance)
   }
 
-  override lazy val count: Long = totalCnt.toLong
+  override def count: Long = totalCnt.toLong
 
-  override lazy val numNonZeros: Vector = Vectors.fromBreeze(nnz)
+  override def numNonZeros: Vector = Vectors.fromBreeze(nnz)
 
-  override lazy val max: Vector = {
-    nnz.iterator.foreach {
-      case (id, count) =>
-        if ((count < totalCnt) && (currMax(id) < 0.0))  currMax(id) = 0.0
+  override def max: Vector = {
+    var i = 0
+    while (i < nnz.length) {
+      if ((nnz(i) < totalCnt) && (currMax(i) < 0.0))  currMax(i) = 0.0
+      i += 1
     }
     Vectors.fromBreeze(currMax)
   }
 
-  override lazy val min: Vector = {
-    nnz.iterator.foreach {
-      case (id, count) =>
-        if ((count < totalCnt) && (currMin(id) > 0.0)) currMin(id) = 0.0
+  override def min: Vector = {
+    var i = 0
+    while (i < nnz.length) {
+      if ((nnz(i) < totalCnt) && (currMin(i) > 0.0)) currMin(i) = 0.0
+      i += 1
     }
     Vectors.fromBreeze(currMin)
   }
@@ -117,15 +128,16 @@ private class VectorRDDStatisticsAggregator(
 
     val deltaMean = currMean - other.currMean
 
-    other.currMean.activeIterator.foreach {
-      case (id, 0.0) =>
-      case (id, value) =>
-        currMean(id) =
-          (currMean(id) * nnz(id) + other.currMean(id) * other.nnz(id)) / (nnz(id) + other.nnz(id))
+    var i = 0
+    while (i < other.currMean.length) {
+      if (other.currMean(i) != 0.0)
+        currMean(i) = (currMean(i) * nnz(i) + other.currMean(i) * other.nnz(i)) /
+          (nnz(i) + other.nnz(i))
+      i += 1
     }
 
-    var i = 0
-    while(i < currM2n.size) {
+    i = 0
+    while (i < currM2n.size) {
       (nnz(i), other.nnz(i)) match {
         case (0.0, 0.0) =>
         case _ => currM2n(i) +=
@@ -134,14 +146,16 @@ private class VectorRDDStatisticsAggregator(
       i += 1
     }
 
-    other.currMax.activeIterator.foreach {
-      case (id, value) =>
-        if (currMax(id) < value) currMax(id) = value
+    i = 0
+    while (i < other.currMax.length) {
+      if (currMax(i) < other.currMax(i)) currMax(i) = other.currMax(i)
+      i += 1
     }
 
-    other.currMin.activeIterator.foreach {
-      case (id, value) =>
-        if (currMin(id) > value) currMin(id) = value
+    i = 0
+    while (i < other.currMin.length) {
+      if (currMin(i) > other.currMin(i)) currMin(i) = other.currMin(i)
+      i += 1
     }
 
     nnz += other.nnz