[SPARK-15413][ML][MLLIB] Change `toBreeze` to `asBreeze` in Vector and Matrix

## What changes were proposed in this pull request?

We're using `asML` to convert the mllib vector/matrix to ml vector/matrix now. Using `as` is more correct given that this conversion actually shares the same underline data structure. As a result, in this PR, `toBreeze` will be changed to `asBreeze`. This is a private API, as a result, it will not affect any user's application.

## How was this patch tested?

unit tests

Author: DB Tsai <dbt@netflix.com>

Closes #13198 from dbtsai/minor.

3 files changed, 16 insertions, 16 deletions

diff --git a/mllib-local/src/main/scala/org/apache/spark/ml/linalg/Matrices.scala b/mllib-local/src/main/scala/org/apache/spark/ml/linalg/Matrices.scala
index a47526d36f..0ea687bbcc 100644
--- a/mllib-local/src/main/scala/org/apache/spark/ml/linalg/Matrices.scala
+++ b/mllib-local/src/main/scala/org/apache/spark/ml/linalg/Matrices.scala
@@ -69,7 +69,7 @@ sealed trait Matrix extends Serializable {
   def rowIter: Iterator[Vector] = this.transpose.colIter
 
   /** Converts to a breeze matrix. */
-  private[ml] def toBreeze: BM[Double]
+  private[ml] def asBreeze: BM[Double]
 
   /** Gets the (i, j)-th element. */
   @Since("2.0.0")
@@ -112,11 +112,11 @@ sealed trait Matrix extends Serializable {
   }
 
   /** A human readable representation of the matrix */
-  override def toString: String = toBreeze.toString()
+  override def toString: String = asBreeze.toString()
 
   /** A human readable representation of the matrix with maximum lines and width */
   @Since("2.0.0")
-  def toString(maxLines: Int, maxLineWidth: Int): String = toBreeze.toString(maxLines, maxLineWidth)
+  def toString(maxLines: Int, maxLineWidth: Int): String = asBreeze.toString(maxLines, maxLineWidth)
 
   /**
    * Map the values of this matrix using a function. Generates a new matrix. Performs the
@@ -202,7 +202,7 @@ class DenseMatrix @Since("2.0.0") (
     this(numRows, numCols, values, false)
 
   override def equals(o: Any): Boolean = o match {
-    case m: Matrix => toBreeze == m.toBreeze
+    case m: Matrix => asBreeze == m.asBreeze
     case _ => false
   }
 
@@ -210,7 +210,7 @@ class DenseMatrix @Since("2.0.0") (
     Seq(numRows, numCols, toArray).##
   }
 
-  private[ml] def toBreeze: BM[Double] = {
+  private[ml] def asBreeze: BM[Double] = {
     if (!isTransposed) {
       new BDM[Double](numRows, numCols, values)
     } else {
@@ -488,14 +488,14 @@ class SparseMatrix @Since("2.0.0") (
       rowIndices: Array[Int],
       values: Array[Double]) = this(numRows, numCols, colPtrs, rowIndices, values, false)
 
-  override def hashCode(): Int = toBreeze.hashCode()
+  override def hashCode(): Int = asBreeze.hashCode()
 
   override def equals(o: Any): Boolean = o match {
-    case m: Matrix => toBreeze == m.toBreeze
+    case m: Matrix => asBreeze == m.asBreeze
     case _ => false
   }
 
-  private[ml] def toBreeze: BM[Double] = {
+  private[ml] def asBreeze: BM[Double] = {
      if (!isTransposed) {
        new BSM[Double](values, numRows, numCols, colPtrs, rowIndices)
      } else {
diff --git a/mllib-local/src/main/scala/org/apache/spark/ml/linalg/Vectors.scala b/mllib-local/src/main/scala/org/apache/spark/ml/linalg/Vectors.scala
index 59f9c2adba..909fec1c06 100644
--- a/mllib-local/src/main/scala/org/apache/spark/ml/linalg/Vectors.scala
+++ b/mllib-local/src/main/scala/org/apache/spark/ml/linalg/Vectors.scala
@@ -92,14 +92,14 @@ sealed trait Vector extends Serializable {
   /**
    * Converts the instance to a breeze vector.
    */
-  private[spark] def toBreeze: BV[Double]
+  private[spark] def asBreeze: BV[Double]
 
   /**
    * Gets the value of the ith element.
    * @param i index
    */
   @Since("2.0.0")
-  def apply(i: Int): Double = toBreeze(i)
+  def apply(i: Int): Double = asBreeze(i)
 
   /**
    * Makes a deep copy of this vector.
@@ -453,7 +453,7 @@ class DenseVector @Since("2.0.0") ( @Since("2.0.0") val values: Array[Double]) e
 
   override def toArray: Array[Double] = values
 
-  private[spark] override def toBreeze: BV[Double] = new BDV[Double](values)
+  private[spark] override def asBreeze: BV[Double] = new BDV[Double](values)
 
   override def apply(i: Int): Double = values(i)
 
@@ -584,7 +584,7 @@ class SparseVector @Since("2.0.0") (
     new SparseVector(size, indices.clone(), values.clone())
   }
 
-  private[spark] override def toBreeze: BV[Double] = new BSV[Double](indices, values, size)
+  private[spark] override def asBreeze: BV[Double] = new BSV[Double](indices, values, size)
 
   override def foreachActive(f: (Int, Double) => Unit): Unit = {
     var i = 0
diff --git a/mllib-local/src/main/scala/org/apache/spark/ml/stat/distribution/MultivariateGaussian.scala b/mllib-local/src/main/scala/org/apache/spark/ml/stat/distribution/MultivariateGaussian.scala
index 383d6d96e8..0be28677ef 100644
--- a/mllib-local/src/main/scala/org/apache/spark/ml/stat/distribution/MultivariateGaussian.scala
+++ b/mllib-local/src/main/scala/org/apache/spark/ml/stat/distribution/MultivariateGaussian.scala
@@ -47,7 +47,7 @@ class MultivariateGaussian @Since("2.0.0") (
     this(Vectors.fromBreeze(mean), Matrices.fromBreeze(cov))
   }
 
-  private val breezeMu = mean.toBreeze.toDenseVector
+  private val breezeMu = mean.asBreeze.toDenseVector
 
   /**
    * Compute distribution dependent constants:
@@ -61,7 +61,7 @@ class MultivariateGaussian @Since("2.0.0") (
    */
   @Since("2.0.0")
   def pdf(x: Vector): Double = {
-    pdf(x.toBreeze)
+    pdf(x.asBreeze)
   }
 
   /**
@@ -69,7 +69,7 @@ class MultivariateGaussian @Since("2.0.0") (
    */
   @Since("2.0.0")
   def logpdf(x: Vector): Double = {
-    logpdf(x.toBreeze)
+    logpdf(x.asBreeze)
   }
 
   /** Returns density of this multivariate Gaussian at given point, x */
@@ -113,7 +113,7 @@ class MultivariateGaussian @Since("2.0.0") (
    * relation to the maximum singular value (same tolerance used by, e.g., Octave).
    */
   private def calculateCovarianceConstants: (BDM[Double], Double) = {
-    val eigSym.EigSym(d, u) = eigSym(cov.toBreeze.toDenseMatrix) // sigma = u * diag(d) * u.t
+    val eigSym.EigSym(d, u) = eigSym(cov.asBreeze.toDenseMatrix) // sigma = u * diag(d) * u.t
 
     // For numerical stability, values are considered to be non-zero only if they exceed tol.
     // This prevents any inverted value from exceeding (eps * n * max(d))^-1