Github user greghogan commented on a diff in the pull request:
https://github.com/apache/flink/pull/2740#discussion_r86391230
--- Diff:
flink-libraries/flink-ml/src/main/scala/org/apache/flink/ml/preprocessing/StringIndexer.scala
---
@@ -0,0 +1,163 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.preprocessing
+
+import org.apache.flink.api.scala._
+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
+
+/**
+ * StringIndexer maps a DataSet[String] to a DataSet[(String,Int)] where
each label is
+ * associated with an index.The indices are in [0,numLabels) and are
ordered by label
+ * frequencies. The most frequent label has index 0.
+ *
+ * @example
+ * {{{
+ * val trainingDS: DataSet[String] =
env.fromCollection(data)
+ * val transformer =
StringIndexer().setHandleInvalid("skip")
+ *
+ * transformer.fit(trainingDS)
+ * val transformedDS = transformer.transform(trainingDS)
+ * }}}
+ *
+ *
+ * You can manage unseen labels using HandleInvalid parameter. If
HandleInvalid is
+ * set to "skip" (see example),then each line containing an unseen label
is skipped.
+ * Otherwise an exception is raised.
+ *
+ * =Parameters=
+ *
+ * -[[HandleInvalid]]: Define how to handle unseen labels: by default is
"skip"
+ *
+ *
+ */
+class StringIndexer extends Transformer[StringIndexer] {
+
+ private[preprocessing] var metricsOption: Option[Map[String, Int]] = None
+
+
+ /**
+ * Set the value to handle unseen labels
+ * @param value set to "skip" if you want to filter line with unseen
labels
+ * @return StringIndexer instance with HandleInvalid value
+ */
+ 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 labels in
the input DataSet.
+ *
+ * @return [[FitOperation]] training the [[StringIndexer]] on string
labels
+ */
+ 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 )
+ }
+ }
+ }
+
+ /**
+ * Count the frequency of each label, sort them in a decreasing order
and assign an index
+ *
+ * @param input input Dataset containing labels
+ * @return a map that returns for each label (key) its index (value)
+ */
+ private def extractIndices(input: DataSet[String]): Map[String, Int] ={
+
+ implicit val resultTypeInformation = createTypeInformation[(String,
Int)]
+
+ val mapper = input
+ .map( s => (s, 1) )
+ .groupBy( 0 )
+ .reduce( (a, b) => (a._1, a._2 + b._2) )
+ .collect( )
--- End diff --
`collect()` returns all results (via an accumulator) to the calling
program. I'm not seeing why this would be necessary.
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