[GitHub] [spark] ozancicek commented on a change in pull request #24939: [SPARK-18569][ML][R] Support RFormula arithmetic, I() and spark functions

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ozancicek commented on a change in pull request #24939: [SPARK-18569][ML][R] Support RFormula arithmetic, I() and spark functions
URL: https://github.com/apache/spark/pull/24939#discussion_r303864360
 
 

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 File path: mllib/src/main/scala/org/apache/spark/ml/feature/RFormula.scala
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 @@ -362,6 +381,16 @@ class RFormulaModel private[feature](
         case _ => true
       }
       StructType(withFeatures.fields :+ StructField($(labelCol), DoubleType, nullable))
+    } else if (resolvedFormula.evalExprs.contains(resolvedFormula.label)) {
+      val spark = SparkSession.builder().getOrCreate()
+      val dummyRDD = spark.sparkContext.parallelize(Seq(Row.empty))
+      val dummyDF = spark.createDataFrame(dummyRDD, schema)
+        .withColumn(resolvedFormula.label, expr(resolvedFormula.label))
+      val nullable = dummyDF.schema(resolvedFormula.label).dataType match {
 
 Review comment:
   In order to create a schema with arbitrary types, I actually borrowed this pattern from here: https://github.com/apache/spark/blob/master/mllib/src/main/scala/org/apache/spark/ml/feature/SQLTransformer.scala#L79
   
   However, the datatype check to determine whether the field should be nullable seems unnecessary here, because only `NumericType` and `BooleanType` seems to be supported, so I modified here to return schema without checking datatype. https://github.com/apache/spark/blob/master/mllib/src/main/scala/org/apache/spark/ml/feature/RFormula.scala#L390  
   
   

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