Github user jkbradley commented on a diff in the pull request:
https://github.com/apache/spark/pull/6339#discussion_r35821538
--- Diff:
mllib/src/main/scala/org/apache/spark/ml/feature/StringIndexer.scala ---
@@ -151,4 +152,79 @@ class StringIndexerModel private[ml] (
val copied = new StringIndexerModel(uid, labels)
copyValues(copied, extra)
}
+
+ /**
+ * Return a model to perform the inverse transformation.
+ * Note: By default we keep the original columns during this
transformation, so the inverse
+ * should only be used on new columns such as predicted labels.
+ */
+ def invert(inputCol: String, outputCol: String): StringIndexerInverse = {
+ new StringIndexerInverse(Some(labels))
+ .setInputCol(inputCol)
+ .setOutputCol(outputCol)
+ }
+}
+
+/**
+ * :: Experimental ::
+ * Transform a provided column back to the original input types using
either the metadata
+ * on the input column, or if provided using the labels supplied by the
user.
+ * Note: By default we keep the original columns during this
transformation,
+ * so the inverse should only be used on new columns such as predicted
labels.
+ */
+@Experimental
+class StringIndexerInverse private[ml] (
+ override val uid: String,
+ val labels: Option[Array[String]]) extends Transformer
--- End diff --
Scala Option tends not to be Java-friendly. I'd prefer we make this a
Param; that will make it Java-friendly and make it clear whether the user has
set it.
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