[SPARK-9544] [MLLIB] add Python API for RFormula

Add Python API for RFormula. Similar to other feature transformers in Python. This is just a thin wrapper over the Scala implementation. ericl MechCoder

Author: Xiangrui Meng <meng@databricks.com>

Closes #7879 from mengxr/SPARK-9544 and squashes the following commits:

3d5ff03 [Xiangrui Meng] add an doctest for . and -
5e969a5 [Xiangrui Meng] fix pydoc
1cd41f8 [Xiangrui Meng] organize imports
3c18b10 [Xiangrui Meng] add Python API for RFormula

1 files changed, 7 insertions, 14 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/feature/RFormula.scala b/mllib/src/main/scala/org/apache/spark/ml/feature/RFormula.scala
index d1726917e4..d5360c9217 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/feature/RFormula.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/feature/RFormula.scala
@@ -19,16 +19,14 @@ package org.apache.spark.ml.feature
 
 import scala.collection.mutable
 import scala.collection.mutable.ArrayBuffer
-import scala.util.parsing.combinator.RegexParsers
 
 import org.apache.spark.annotation.Experimental
-import org.apache.spark.ml.{Estimator, Model, Transformer, Pipeline, PipelineModel, PipelineStage}
+import org.apache.spark.ml.{Estimator, Model, Pipeline, PipelineModel, PipelineStage, Transformer}
 import org.apache.spark.ml.param.{Param, ParamMap}
 import org.apache.spark.ml.param.shared.{HasFeaturesCol, HasLabelCol}
 import org.apache.spark.ml.util.Identifiable
 import org.apache.spark.mllib.linalg.VectorUDT
 import org.apache.spark.sql.DataFrame
-import org.apache.spark.sql.functions._
 import org.apache.spark.sql.types._
 
 /**
@@ -63,31 +61,26 @@ class RFormula(override val uid: String) extends Estimator[RFormulaModel] with R
    */
   val formula: Param[String] = new Param(this, "formula", "R model formula")
 
-  private var parsedFormula: Option[ParsedRFormula] = None
-
   /**
    * Sets the formula to use for this transformer. Must be called before use.
    * @group setParam
    * @param value an R formula in string form (e.g. "y ~ x + z")
    */
-  def setFormula(value: String): this.type = {
-    parsedFormula = Some(RFormulaParser.parse(value))
-    set(formula, value)
-    this
-  }
+  def setFormula(value: String): this.type = set(formula, value)
 
   /** @group getParam */
   def getFormula: String = $(formula)
 
   /** Whether the formula specifies fitting an intercept. */
   private[ml] def hasIntercept: Boolean = {
-    require(parsedFormula.isDefined, "Must call setFormula() first.")
-    parsedFormula.get.hasIntercept
+    require(isDefined(formula), "Formula must be defined first.")
+    RFormulaParser.parse($(formula)).hasIntercept
   }
 
   override def fit(dataset: DataFrame): RFormulaModel = {
-    require(parsedFormula.isDefined, "Must call setFormula() first.")
-    val resolvedFormula = parsedFormula.get.resolve(dataset.schema)
+    require(isDefined(formula), "Formula must be defined first.")
+    val parsedFormula = RFormulaParser.parse($(formula))
+    val resolvedFormula = parsedFormula.resolve(dataset.schema)
     // StringType terms and terms representing interactions need to be encoded before assembly.
     // TODO(ekl) add support for feature interactions
     val encoderStages = ArrayBuffer[PipelineStage]()