[Spark-4995] Replace Vector.toBreeze.activeIterator with foreachActive

mllib/src/main/scala/org/apache/spark/mllib/linalg/distributed/IndexedRowMatrix.scala

@@ -142,7 +142,7 @@ class IndexedRowMatrix(
     val mat = BDM.zeros[Double](m, n)
     rows.collect().foreach { case IndexedRow(rowIndex, vector) =>
       val i = rowIndex.toInt
-      vector.toBreeze.activeIterator.foreach { case (j, v) =>
+      vector.foreachActive { case (j, v) =>
         mat(i, j) = v
       }
     }

mllib/src/main/scala/org/apache/spark/mllib/linalg/distributed/RowMatrix.scala

@@ -588,8 +588,8 @@ class RowMatrix(
     val n = numCols().toInt
     val mat = BDM.zeros[Double](m, n)
     var i = 0
-    rows.collect().foreach { v =>
-      v.toBreeze.activeIterator.foreach { case (j, v) =>
+    rows.collect().foreach { vector =>
+      vector.foreachActive { case (j, v) =>
         mat(i, j) = v
       }
       i += 1

mllib/src/main/scala/org/apache/spark/mllib/util/MLUtils.scala

@@ -154,10 +154,12 @@ object MLUtils {
   def saveAsLibSVMFile(data: RDD[LabeledPoint], dir: String) {
     // TODO: allow to specify label precision and feature precision.
     val dataStr = data.map { case LabeledPoint(label, features) =>
-      val featureStrings = features.toBreeze.activeIterator.map { case (i, v) =>
-        s"${i + 1}:$v"
+      val sb = new StringBuilder(label.toString)
+      features.foreachActive { case (i, v) =>
+        sb += ' '
+        sb ++= s"${i + 1}:$v"
       }
-      (Iterator(label) ++ featureStrings).mkString(" ")
+      sb.mkString
     }
     dataStr.saveAsTextFile(dir)
   }