[SPARK-11497][MLLIB][PYTHON] PySpark RowMatrix Constructor Has Type Erasure Issue

dusenberrymw · jkbradley · commit bfcc8cfee721 · 2015-12-11T14:21:48.000-08:00
As noted in PR apache#9441, implementing `tallSkinnyQR` uncovered a bug with our PySpark `RowMatrix` constructor. As discussed on the dev list [here](http://apache-spark-developers-list.1001551.n3.nabble.com/K-Means-And-Class-Tags-td10038.html), there appears to be an issue with type erasure with RDDs coming from Java, and by extension from PySpark. Although we are attempting to construct a `RowMatrix` from an `RDD[Vector]` in [PythonMLlibAPI](https://github.com/apache/spark/blob/master/mllib/src/main/scala/org/apache/spark/mllib/api/python/PythonMLLibAPI.scala#L1115), the `Vector` type is erased, resulting in an `RDD[Object]`. Thus, when calling Scala's `tallSkinnyQR` from PySpark, we get a Java `ClassCastException` in which an `Object` cannot be cast to a Spark `Vector`. As noted in the aforementioned dev list thread, this issue was also encountered with `DecisionTrees`, and the fix involved an explicit `retag` of the RDD with a `Vector` type. `IndexedRowMatrix` and `CoordinateMatrix` do not appear to have this issue likely due to their related helper functions in `PythonMLlibAPI` creating the RDDs explicitly from DataFrames with pattern matching, thus preserving the types. This PR currently contains that retagging fix applied to the `createRowMatrix` helper function in `PythonMLlibAPI`. This PR blocks apache#9441, so once this is merged, the other can be rebased. cc holdenk Author: Mike Dusenberry <mwdusenb@us.ibm.com> Closes apache#9458 from dusenberrymw/SPARK-11497_PySpark_RowMatrix_Constructor_Has_Type_Erasure_Issue. (cherry picked from commit 1b82203) Signed-off-by: Joseph K. Bradley <joseph@databricks.com>
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/api/python/PythonMLLibAPI.scala b/mllib/src/main/scala/org/apache/spark/mllib/api/python/PythonMLLibAPI.scala
@@ -1143,7 +1143,7 @@ private[python] class PythonMLLibAPI extends Serializable {
    * Wrapper around RowMatrix constructor.
    */
   def createRowMatrix(rows: JavaRDD[Vector], numRows: Long, numCols: Int): RowMatrix = {
-    new RowMatrix(rows.rdd, numRows, numCols)
+    new RowMatrix(rows.rdd.retag(classOf[Vector]), numRows, numCols)
   }
 
   /**

Original file line number	Diff line number	Diff line change
`@@ -1143,7 +1143,7 @@ private[python] class PythonMLLibAPI extends Serializable {`
`1143`	`1143`	`* Wrapper around RowMatrix constructor.`
`1144`	`1144`	`*/`
`1145`	`1145`	`def createRowMatrix(rows: JavaRDD[Vector], numRows: Long, numCols: Int): RowMatrix = {`
`1146`		`- new RowMatrix(rows.rdd, numRows, numCols)`
	`1146`	`+ new RowMatrix(rows.rdd.retag(classOf[Vector]), numRows, numCols)`
`1147`	`1147`	`}`
`1148`	`1148`
`1149`	`1149`	`/**`