[MLlib] [SPARK-5301] Missing conversions and operations on IndexedRowMatrix and CoordinateMatrix

* Transpose is missing from CoordinateMatrix (this is cheap to compute, so it should be there)
* IndexedRowMatrix should be convertable to CoordinateMatrix (conversion added)

Tests for both added.

Author: Reza Zadeh <reza@databricks.com>

Closes #4089 from rezazadeh/matutils and squashes the following commits:

ec5238b [Reza Zadeh] Array -> Iterator to avoid temp array
3ce0b5d [Reza Zadeh] Array -> Iterator
bbc907a [Reza Zadeh] Use 'i' for index, and zipWithIndex
cb10ae5 [Reza Zadeh] remove unnecessary import
a7ae048 [Reza Zadeh] Missing linear algebra utilities

2 files changed, 13 insertions, 0 deletions

diff --git a/mllib/src/test/scala/org/apache/spark/mllib/linalg/distributed/CoordinateMatrixSuite.scala b/mllib/src/test/scala/org/apache/spark/mllib/linalg/distributed/CoordinateMatrixSuite.scala
index f8709751ef..80bef814ce 100644
--- a/mllib/src/test/scala/org/apache/spark/mllib/linalg/distributed/CoordinateMatrixSuite.scala
+++ b/mllib/src/test/scala/org/apache/spark/mllib/linalg/distributed/CoordinateMatrixSuite.scala
@@ -73,6 +73,11 @@ class CoordinateMatrixSuite extends FunSuite with MLlibTestSparkContext {
     assert(mat.toBreeze() === expected)
   }
 
+  test("transpose") {
+    val transposed = mat.transpose()
+    assert(mat.toBreeze().t === transposed.toBreeze())
+  }
+
   test("toIndexedRowMatrix") {
     val indexedRowMatrix = mat.toIndexedRowMatrix()
     val expected = BDM(
diff --git a/mllib/src/test/scala/org/apache/spark/mllib/linalg/distributed/IndexedRowMatrixSuite.scala b/mllib/src/test/scala/org/apache/spark/mllib/linalg/distributed/IndexedRowMatrixSuite.scala
index 741cd4997b..b86c2ca5ff 100644
--- a/mllib/src/test/scala/org/apache/spark/mllib/linalg/distributed/IndexedRowMatrixSuite.scala
+++ b/mllib/src/test/scala/org/apache/spark/mllib/linalg/distributed/IndexedRowMatrixSuite.scala
@@ -80,6 +80,14 @@ class IndexedRowMatrixSuite extends FunSuite with MLlibTestSparkContext {
     assert(rowMat.rows.collect().toSeq === data.map(_.vector).toSeq)
   }
 
+  test("toCoordinateMatrix") {
+    val idxRowMat = new IndexedRowMatrix(indexedRows)
+    val coordMat = idxRowMat.toCoordinateMatrix()
+    assert(coordMat.numRows() === m)
+    assert(coordMat.numCols() === n)
+    assert(coordMat.toBreeze() === idxRowMat.toBreeze())
+  }
+
   test("multiply a local matrix") {
     val A = new IndexedRowMatrix(indexedRows)
     val B = Matrices.dense(3, 2, Array(0.0, 1.0, 2.0, 3.0, 4.0, 5.0))