[SPARK-13927][MLLIB] add row/column iterator to local matrices

## What changes were proposed in this pull request?

Add row/column iterator to local matrices to simplify tasks like BlockMatrix => RowMatrix conversion. It handles dense and sparse matrices properly.

## How was this patch tested?

Unit tests on sparse and dense matrix.

cc: dbtsai

Author: Xiangrui Meng <meng@databricks.com>

Closes #11757 from mengxr/SPARK-13927.

1 files changed, 13 insertions, 0 deletions

diff --git a/mllib/src/test/scala/org/apache/spark/mllib/linalg/MatricesSuite.scala b/mllib/src/test/scala/org/apache/spark/mllib/linalg/MatricesSuite.scala
index 1833cf3833..a02b8c9635 100644
--- a/mllib/src/test/scala/org/apache/spark/mllib/linalg/MatricesSuite.scala
+++ b/mllib/src/test/scala/org/apache/spark/mllib/linalg/MatricesSuite.scala
@@ -494,4 +494,17 @@ class MatricesSuite extends SparkFunSuite {
     assert(sm1.numNonzeros === 1)
     assert(sm1.numActives === 3)
   }
+
+  test("row/col iterator") {
+    val dm = new DenseMatrix(3, 2, Array(0, 1, 2, 3, 4, 0))
+    val sm = dm.toSparse
+    val rows = Seq(Vectors.dense(0, 3), Vectors.dense(1, 4), Vectors.dense(2, 0))
+    val cols = Seq(Vectors.dense(0, 1, 2), Vectors.dense(3, 4, 0))
+    for (m <- Seq(dm, sm)) {
+      assert(m.rowIter.toSeq === rows)
+      assert(m.colIter.toSeq === cols)
+      assert(m.transpose.rowIter.toSeq === cols)
+      assert(m.transpose.colIter.toSeq === rows)
+    }
+  }
 }