Github user jkbradley commented on a diff in the pull request:
https://github.com/apache/spark/pull/6339#discussion_r35581918
--- Diff:
mllib/src/main/scala/org/apache/spark/ml/feature/StringIndexer.scala ---
@@ -151,4 +167,64 @@ 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 invert should only be needed if you do something beyond simply
+ * applying the original transformation.
+ */
+ def invert(): StringIndexerInvertModel = {
+ new StringIndexerInvertModel(uid, labels)
+ .setInputCol(getOutputCol)
+ .setOutputCol(getInputCol)
+ }
+}
+
+class StringIndexerInvertModel private[ml] (
+ override val uid: String,
+ labels: Array[String]) extends Model[StringIndexerInvertModel] with
StringIndexerBase {
+
+ /** @group setParam */
+ def setInputCol(value: String): this.type = set(inputCol, value)
+
+ /** @group setParam */
+ def setOutputCol(value: String): this.type = set(outputCol, value)
+
+
+ private val indexToLabel: OpenHashMap[Double, String] = {
+ val n = labels.length
+ val map = new OpenHashMap[Double, String](n)
+ var i = 0
+ while (i < n) {
+ map.update(i, labels(i))
+ i += 1
+ }
+ map
+ }
+
+ override def transformSchema(schema: StructType): StructType = {
+ invertSchema(schema)
+ }
+
+ override def transform(dataset: DataFrame): DataFrame = {
+ val indexer = udf { index: Double =>
+ if (indexToLabel.contains(index)) {
+ indexToLabel(index)
+ } else {
+ throw new SparkException(s"Unseen index: $index ??")
+ }
+ }
+ val outputColName = $(outputCol)
+ val metadata = NominalAttribute.defaultAttr
+ .withName(outputColName).withValues(labels).toMetadata()
+ dataset.select(col("*"),
+ indexer(dataset($(inputCol)).cast(StringType)).as(outputColName,
metadata))
+ }
+
+ override def copy(extra: ParamMap): StringIndexerInvertModel = {
+ val copied = new StringIndexerInvertModel(uid, labels)
+ copyValues(copied, extra)
--- End diff --
call setParent, if a parent is available
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