/*
 * 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();
    }
}
