content: /*
   * 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.spark.examples.ml;
  
  import org.apache.spark.sql.Dataset;
  import org.apache.spark.sql.SparkSession;
  
  // $example on$
  import java.util.Arrays;
  import java.util.List;
  
  import org.apache.spark.ml.attribute.Attribute;
  import org.apache.spark.ml.feature.IndexToString;
  import org.apache.spark.ml.feature.StringIndexer;
  import org.apache.spark.ml.feature.StringIndexerModel;
  import org.apache.spark.sql.Row;
  import org.apache.spark.sql.RowFactory;
  import org.apache.spark.sql.types.DataTypes;
  import org.apache.spark.sql.types.Metadata;
  import org.apache.spark.sql.types.StructField;
  import org.apache.spark.sql.types.StructType;
  // $example off$
  
  public class JavaIndexToStringExample {
    public static void main(String[] args) {
      SparkSession spark = SparkSession
        .builder()
        .appName("JavaIndexToStringExample")
        .getOrCreate();
  
      // $example on$
      List<Row> data = Arrays.asList(
        RowFactory.create(0, "a"),
        RowFactory.create(1, "b"),
        RowFactory.create(2, "c"),
        RowFactory.create(3, "a"),
        RowFactory.create(4, "a"),
        RowFactory.create(5, "c")
      );
      StructType schema = new StructType(new StructField[]{
        new StructField("id", DataTypes.IntegerType, false, Metadata.empty()),
        new StructField("category", DataTypes.StringType, false, Metadata.empty())
      });
      Dataset<Row> df = spark.createDataFrame(data, schema);
  
      StringIndexerModel indexer = new StringIndexer()
        .setInputCol("category")
        .setOutputCol("categoryIndex")
        .fit(df);
      Dataset<Row> indexed = indexer.transform(df);
  
      System.out.println("Transformed string column '" + indexer.getInputCol() + "' " +
          "to indexed column '" + indexer.getOutputCol() + "'");
      indexed.show();
  
      StructField inputColSchema = indexed.schema().apply(indexer.getOutputCol());
      System.out.println("StringIndexer will store labels in output column metadata: " +
          Attribute.fromStructField(inputColSchema).toString() + "\n");
  
      IndexToString converter = new IndexToString()
        .setInputCol("categoryIndex")
        .setOutputCol("originalCategory");
      Dataset<Row> converted = converter.transform(indexed);
  
      System.out.println("Transformed indexed column '" + converter.getInputCol() + "' back to " +
          "original string column '" + converter.getOutputCol() + "' using labels in metadata");
      converted.select("id", "categoryIndex", "originalCategory").show();
  
      // $example off$
      spark.stop();
    }
  }
  