Added a comment about breeze lazy slicing

amplab · Nov 25, 2015 · 74ab533 · 74ab533
1 parent d9b013d
commit 74ab533
Showing 1 changed file with 4 additions and 0 deletions.
diff --git a/src/main/scala/utils/MatrixUtils.scala b/src/main/scala/utils/MatrixUtils.scala
@@ -20,6 +20,8 @@ object MatrixUtils extends Serializable {
    */
   def matrixToRowArray[T : ClassTag](mat: DenseMatrix[T]): Array[DenseVector[T]] = {
     val matT = mat.t
+    // The explicit copy of the vector is necessary because otherwise Breeze slices
+    // lazily, leading to inflated serialization size (A serious issue w/ spark)
     (0 until mat.rows).toArray.map(x => DenseVector(matT(::, x).toArray))
   }
 
@@ -29,6 +31,8 @@ object MatrixUtils extends Serializable {
    * @return Array of columns.
    */
   def matrixToColArray[T : ClassTag](mat: DenseMatrix[T]): Array[DenseVector[T]] = {
+    // The explicit copy of the vector is necessary because otherwise Breeze slices
+    // lazily, leading to inflated serialization size (A serious issue w/ spark)
     (0 until mat.cols).toArray.map(x => DenseVector(mat(::, x).toArray))
   }