Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/8293#discussion_r37425854
--- Diff: docs/ml-features.md ---
@@ -1386,6 +1386,102 @@ print(output.select("features", "clicked").first())
{% endhighlight %}
</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
--- End diff --
Need to have at least two countries.
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