[SPARK-10573] [ML] IndexToString output schema should be StringType

Fixes bug where IndexToString output schema was DoubleType. Correct me if I'm wrong, but it doesn't seem like the output needs to have any "ML Attribute" metadata.

Author: Nick Pritchard <nicholas.pritchard@falkonry.com>

Closes #8751 from pnpritchard/SPARK-10573.

2 files changed, 10 insertions, 3 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/feature/StringIndexer.scala b/mllib/src/main/scala/org/apache/spark/ml/feature/StringIndexer.scala
index 3a4ab9a857..2b1592930e 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/feature/StringIndexer.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/feature/StringIndexer.scala
@@ -27,7 +27,7 @@ import org.apache.spark.ml.Transformer
 import org.apache.spark.ml.util.Identifiable
 import org.apache.spark.sql.DataFrame
 import org.apache.spark.sql.functions._
-import org.apache.spark.sql.types.{DoubleType, NumericType, StringType, StructType}
+import org.apache.spark.sql.types._
 import org.apache.spark.util.collection.OpenHashMap
 
 /**
@@ -229,8 +229,7 @@ class IndexToString private[ml] (
     val outputColName = $(outputCol)
     require(inputFields.forall(_.name != outputColName),
       s"Output column $outputColName already exists.")
-    val attr = NominalAttribute.defaultAttr.withName($(outputCol))
-    val outputFields = inputFields :+ attr.toStructField()
+    val outputFields = inputFields :+ StructField($(outputCol), StringType)
     StructType(outputFields)
   }
 
diff --git a/mllib/src/test/scala/org/apache/spark/ml/feature/StringIndexerSuite.scala b/mllib/src/test/scala/org/apache/spark/ml/feature/StringIndexerSuite.scala
index 05e05bdc64..ddcdb5f421 100644
--- a/mllib/src/test/scala/org/apache/spark/ml/feature/StringIndexerSuite.scala
+++ b/mllib/src/test/scala/org/apache/spark/ml/feature/StringIndexerSuite.scala
@@ -17,6 +17,7 @@
 
 package org.apache.spark.ml.feature
 
+import org.apache.spark.sql.types.{StringType, StructType, StructField, DoubleType}
 import org.apache.spark.{SparkException, SparkFunSuite}
 import org.apache.spark.ml.attribute.{Attribute, NominalAttribute}
 import org.apache.spark.ml.param.ParamsSuite
@@ -165,4 +166,11 @@ class StringIndexerSuite extends SparkFunSuite with MLlibTestSparkContext {
         assert(a === b)
     }
   }
+
+  test("IndexToString.transformSchema (SPARK-10573)") {
+    val idxToStr = new IndexToString().setInputCol("input").setOutputCol("output")
+    val inSchema = StructType(Seq(StructField("input", DoubleType)))
+    val outSchema = idxToStr.transformSchema(inSchema)
+    assert(outSchema("output").dataType === StringType)
+  }
 }