[SPARK-13010][ML][SPARKR] Implement a simple wrapper of AFTSurvivalRegression in SparkR

## What changes were proposed in this pull request?
This PR continues the work in #11447, we implemented the wrapper of ```AFTSurvivalRegression``` named ```survreg``` in SparkR.

## How was this patch tested?
Test against output from R package survival's survreg.

cc mengxr felixcheung

Close #11447

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #11932 from yanboliang/spark-13010-new.

1 files changed, 99 insertions, 0 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/r/AFTSurvivalRegressionWrapper.scala b/mllib/src/main/scala/org/apache/spark/ml/r/AFTSurvivalRegressionWrapper.scala
new file mode 100644
index 0000000000..40590e71c4
--- /dev/null
+++ b/mllib/src/main/scala/org/apache/spark/ml/r/AFTSurvivalRegressionWrapper.scala
@@ -0,0 +1,99 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.ml.r
+
+import org.apache.spark.SparkException
+import org.apache.spark.ml.{Pipeline, PipelineModel}
+import org.apache.spark.ml.attribute.AttributeGroup
+import org.apache.spark.ml.feature.RFormula
+import org.apache.spark.ml.regression.{AFTSurvivalRegression, AFTSurvivalRegressionModel}
+import org.apache.spark.sql.DataFrame
+
+private[r] class AFTSurvivalRegressionWrapper private (
+    pipeline: PipelineModel,
+    features: Array[String]) {
+
+  private val aftModel: AFTSurvivalRegressionModel =
+    pipeline.stages(1).asInstanceOf[AFTSurvivalRegressionModel]
+
+  lazy val rCoefficients: Array[Double] = if (aftModel.getFitIntercept) {
+    Array(aftModel.intercept) ++ aftModel.coefficients.toArray ++ Array(math.log(aftModel.scale))
+  } else {
+    aftModel.coefficients.toArray ++ Array(math.log(aftModel.scale))
+  }
+
+  lazy val rFeatures: Array[String] = if (aftModel.getFitIntercept) {
+    Array("(Intercept)") ++ features ++ Array("Log(scale)")
+  } else {
+    features ++ Array("Log(scale)")
+  }
+
+  def transform(dataset: DataFrame): DataFrame = {
+    pipeline.transform(dataset)
+  }
+}
+
+private[r] object AFTSurvivalRegressionWrapper {
+
+  private def formulaRewrite(formula: String): (String, String) = {
+    var rewritedFormula: String = null
+    var censorCol: String = null
+
+    val regex = """Surv\(([^,]+), ([^,]+)\) ~ (.+)""".r
+    try {
+      val regex(label, censor, features) = formula
+      // TODO: Support dot operator.
+      if (features.contains(".")) {
+        throw new UnsupportedOperationException(
+          "Terms of survreg formula can not support dot operator.")
+      }
+      rewritedFormula = label.trim + "~" + features.trim
+      censorCol = censor.trim
+    } catch {
+      case e: MatchError =>
+        throw new SparkException(s"Could not parse formula: $formula")
+    }
+
+    (rewritedFormula, censorCol)
+  }
+
+
+  def fit(formula: String, data: DataFrame): AFTSurvivalRegressionWrapper = {
+
+    val (rewritedFormula, censorCol) = formulaRewrite(formula)
+
+    val rFormula = new RFormula().setFormula(rewritedFormula)
+    val rFormulaModel = rFormula.fit(data)
+
+    // get feature names from output schema
+    val schema = rFormulaModel.transform(data).schema
+    val featureAttrs = AttributeGroup.fromStructField(schema(rFormula.getFeaturesCol))
+      .attributes.get
+    val features = featureAttrs.map(_.name.get)
+
+    val aft = new AFTSurvivalRegression()
+      .setCensorCol(censorCol)
+      .setFitIntercept(rFormula.hasIntercept)
+
+    val pipeline = new Pipeline()
+      .setStages(Array(rFormulaModel, aft))
+      .fit(data)
+
+    new AFTSurvivalRegressionWrapper(pipeline, features)
+  }
+}