Github user greghogan commented on a diff in the pull request:
https://github.com/apache/flink/pull/2740#discussion_r87860878
--- Diff:
flink-libraries/flink-ml/src/main/scala/org/apache/flink/ml/preprocessing/StringIndexer.scala
---
@@ -0,0 +1,108 @@
+package org.apache.flink.ml.preprocessing
+
+import org.apache.flink.api.scala._
+import org.apache.flink.api.scala.extensions.acceptPartialFunctions
+import org.apache.flink.api.scala.utils._
+import org.apache.flink.ml.common.{Parameter, ParameterMap}
+import org.apache.flink.ml.pipeline.{FitOperation,
TransformDataSetOperation, Transformer}
+import org.apache.flink.ml.preprocessing.StringIndexer.HandleInvalid
+
+import scala.collection.immutable.Seq
+
+/**
+ * String Indexer
+ */
+class StringIndexer extends Transformer[StringIndexer] {
+
+ private[preprocessing] var metricsOption: Option[DataSet[(String,
Long)]] = None
+
+
+ def setHandleInvalid(value: String): this.type ={
+ parameters.add( HandleInvalid, value )
+ this
+ }
+
+}
+
+object StringIndexer {
+
+ case object HandleInvalid extends Parameter[String] {
+ val defaultValue: Option[String] = Some( "skip" )
+ }
+
+ // ==================================== Factory methods
==========================================
+
+ def apply(): StringIndexer ={
+ new StringIndexer( )
+ }
+
+ // ====================================== Operations
=============================================
+
+ /**
+ * Trains [[StringIndexer]] by learning the count of each string in the
input DataSet.
+ */
+
+ implicit def fitStringIndexer ={
+ new FitOperation[StringIndexer, String] {
+ def fit(instance: StringIndexer, fitParameters: ParameterMap, input:
DataSet[String]):Unit ={
+ val metrics = extractIndices( input )
+ instance.metricsOption = Some( metrics )
+ }
+ }
+ }
+
+ private def extractIndices(input: DataSet[String]): DataSet[(String,
Long)] = {
+
+ val mapping = input
+ .mapWith( s => (s, 1) )
+ .groupBy( 0 )
+ .reduce( (a, b) => (a._1, a._2 + b._2) )
--- End diff --
Can this be replaced with `.sum(1)`?
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