Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/8293#discussion_r37463102
--- Diff: docs/ml-features.md ---
@@ -1387,5 +1387,107 @@ print(output.select("features", "clicked").first())
</div>
</div>
+## RFormula
+
+`RFormula` selects columns specified by an [R model
formula](https://stat.ethz.ch/R-manual/R-devel/library/stats/html/formula.html).
It produces a vector column of features and a double column of labels. Like
when formulas are used in R for linear regression, string input columns will be
one-hot encoded, and numeric columns will be cast to doubles. If not already
present in the DataFrame, the output label column will be created from the
specified response variable in the formula.
+
+**Examples**
+
+Assume that we have a DataFrame with the columns `id`, `country`, `hour`,
and `clicked`:
+
+~~~
+id | country | hour | clicked
+---|---------|------|---------
+ 7 | "US" | 18 | 1.0
+ 8 | "CA" | 12 | 0.0
+~~~
+
+If we use `RFormula` with a formula string of `clicked ~ country + hour`,
which indicates that we want to
+predict `clicked` based on `country` and `hour`, after transformation we
should get the following DataFrame:
+
+~~~
+id | country | hour | clicked | label | features
+---|---------|------|---------|-------|-----------------------------
+ 7 | "US" | 18 | 1.0 | 1.0 | [0.0, 1.0, 18.0]
+ 8 | "CA" | 12 | 0.0 | 0.0 | [1.0, 0.0, 12.0]
+~~~
+
+<div class="codetabs">
+<div data-lang="scala" markdown="1">
+
+[`RFormula`](api/scala/index.html#org.apache.spark.ml.feature.RFormula)
takes an R formula string, and optional parameters for the names of its output
columns.
+
+{% highlight scala %}
+import org.apache.spark.ml.feature.RFormula
+
+val dataset = sqlContext.createDataFrame(
+ Seq((7, "US", 18, 1.0)),
+ Seq((8, "CA", 12, 0.0))
+).toDF("id", "country", "hour", "clicked")
+val formula = new RFormula()
+ .setFormula("clicked ~ country + hour")
+ .setFeaturesCol("features")
+ .setLabelCol("label")
+val output = formula.fit(dataset).transform(dataset)
+println(output.select("features", "label").first())
--- End diff --
`output.select("features", "label").show()` because there are more than one
instance. The output should be
~~~
+----------+-----+
| features|label|
+----------+-----+
|[0.0,18.0]| 1.0|
|[1.0,12.0]| 0.0|
+----------+-----+
~~~
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