[SPARK-11902][ML] Unhandled case in VectorAssembler#transform

There is an unhandled case in the transform method of VectorAssembler if one of the input columns doesn't have one of the supported type DoubleType, NumericType, BooleanType or VectorUDT.

So, if you try to transform a column of StringType you get a cryptic "scala.MatchError: StringType".

This PR aims to fix this, throwing a SparkException when dealing with an unknown column type.

Author: BenFradet <benjamin.fradet@gmail.com>

Closes #9885 from BenFradet/SPARK-11902.

mllib/src/main/scala/org/apache/spark/ml/feature/VectorAssembler.scala

@@ -84,6 +84,8 @@ class VectorAssembler(override val uid: String)
             val numAttrs = group.numAttributes.getOrElse(first.getAs[Vector](index).size)
             Array.fill(numAttrs)(NumericAttribute.defaultAttr)
           }
+        case otherType =>
+          throw new SparkException(s"VectorAssembler does not support the $otherType type")
       }
     }
     val metadata = new AttributeGroup($(outputCol), attrs).toMetadata()

mllib/src/test/scala/org/apache/spark/ml/feature/VectorAssemblerSuite.scala

@@ -69,6 +69,17 @@ class VectorAssemblerSuite
     }
   }
 
+  test("transform should throw an exception in case of unsupported type") {
+    val df = sqlContext.createDataFrame(Seq(("a", "b", "c"))).toDF("a", "b", "c")
+    val assembler = new VectorAssembler()
+      .setInputCols(Array("a", "b", "c"))
+      .setOutputCol("features")
+    val thrown = intercept[SparkException] {
+      assembler.transform(df)
+    }
+    assert(thrown.getMessage contains "VectorAssembler does not support the StringType type")
+  }
+
   test("ML attributes") {
     val browser = NominalAttribute.defaultAttr.withValues("chrome", "firefox", "safari")
     val hour = NumericAttribute.defaultAttr.withMin(0.0).withMax(24.0)