From f4f5ebb59b10ab09414690498bdeadceb94ca2e5 Mon Sep 17 00:00:00 2001
From: Liang-Chi Hsieh <viirya@gmail.com>
Date: Thu, 11 Dec 2014 20:46:00 +0800
Subject: [PATCH] Follow BLAS.dot pattern to replace intersect, diff with
 while-loop.

---
 .../org/apache/spark/mllib/util/MLUtils.scala | 77 +++++++++++--------
 1 file changed, 43 insertions(+), 34 deletions(-)

diff --git a/mllib/src/main/scala/org/apache/spark/mllib/util/MLUtils.scala b/mllib/src/main/scala/org/apache/spark/mllib/util/MLUtils.scala
index 7b25ef6ecbc62..89fc88a1cb60b 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/util/MLUtils.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/util/MLUtils.scala
@@ -271,32 +271,34 @@ object MLUtils {
     var squaredDistance = 0.0
     (v1, v2) match { 
       case (v1: SparseVector, v2: SparseVector) =>
-        var count = 0
-        var indices = v1.indices.intersect(v2.indices)
-
-        while (count < indices.length) {
-          val idx = indices(count)
-          val score = v1(idx) - v2(idx)
-          squaredDistance += score * score
-          count += 1
-        }
-
-        count = 0
-        indices = v1.indices.diff(v2.indices)
-        while (count < indices.length) {
-          val idx = indices(count)
-          val score = v1(idx)
-          squaredDistance += score * score
-          count += 1
-        }
+        val v1Values = v1.values
+        val v1Indices = v1.indices
+        val v2Values = v2.values
+        val v2Indices = v2.indices
+        val nnzv1 = v1Indices.size
+        val nnzv2 = v2Indices.size
         
-        count = 0
-        indices = v2.indices.diff(v1.indices)
-        while (count < indices.length) {
-          val idx = indices(count)
-          val score = v2(idx)
-          squaredDistance += score * score
-          count += 1
+        var kv1 = 0
+        var kv2 = 0
+        var score = 0.0
+        while (kv1 < nnzv1) {
+          val iv1 = v1Indices(kv1)
+ 
+          if (kv2 >= nnzv2 || iv1 < v2Indices(kv2)) {
+            score = v1Values(kv1)
+            squaredDistance += score * score
+          }
+          while (kv2 < nnzv2 && v2Indices(kv2) < iv1) {
+            score = v2Values(kv2)
+            squaredDistance += score * score
+            kv2 += 1
+          }
+          if (kv2 < nnzv2 && v2Indices(kv2) == iv1) {
+            score = v1Values(kv1) - v2Values(kv2)
+            squaredDistance += score * score
+            kv2 += 1
+          }
+          kv1 += 1
         }
 
       case (v1: SparseVector, v2: DenseVector) if v1.indices.length / v1.size < 0.5 =>
@@ -321,21 +323,28 @@ object MLUtils {
     var squaredDistance = 0.0
     var count = 0
     var indices = v1.indices
-
+    var score = 0.0
     while (count < indices.length) {
       val idx = indices(count)
-      val score = v1(idx) - v2(idx)
+      score = v1(idx) - v2(idx)
       squaredDistance += score * score
       count += 1
     }
 
-    count = 0
-    indices = (0 to v2.size - 1).toArray.diff(v1.indices)
-    while (count < indices.length) {
-      val idx = indices(count)
-      val score = v2(idx)
-      squaredDistance += score * score
-      count += 1
+    var kv1 = 0
+    var kv2 = 0
+    var iv1 = indices(kv1)
+    val nnzv2 = v2.size
+    while (kv2 < nnzv2) {
+      if (kv2 < iv1 || kv2 > iv1) {
+        score = v2(kv2)
+        squaredDistance += score * score
+      }
+      if (kv2 == iv1 && kv1 < indices.length - 1) {
+        kv1 += 1
+        iv1 = indices(kv1)
+      }
+      kv2 += 1
     }
     squaredDistance
   }