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.mllib;
  
  import com.google.common.collect.ImmutableMap;
  import org.apache.spark.SparkConf;
  import org.apache.spark.api.java.JavaSparkContext;
  
  // $example on$
  import java.util.*;
  
  import scala.Tuple2;
  
  import org.apache.spark.api.java.JavaPairRDD;
  // $example off$
  
  public class JavaStratifiedSamplingExample {
    public static void main(String[] args) {
  
      SparkConf conf = new SparkConf().setAppName("JavaStratifiedSamplingExample");
      JavaSparkContext jsc = new JavaSparkContext(conf);
  
      @SuppressWarnings("unchecked")
      // $example on$
      List<Tuple2<Integer, Character>> list = Arrays.asList(
          new Tuple2<>(1, 'a'),
          new Tuple2<>(1, 'b'),
          new Tuple2<>(2, 'c'),
          new Tuple2<>(2, 'd'),
          new Tuple2<>(2, 'e'),
          new Tuple2<>(3, 'f')
      );
  
      JavaPairRDD<Integer, Character> data = jsc.parallelizePairs(list);
  
      // specify the exact fraction desired from each key Map<K, Double>
      ImmutableMap<Integer, Double> fractions = ImmutableMap.of(1, 0.1, 2, 0.6, 3, 0.3);
  
      // Get an approximate sample from each stratum
      JavaPairRDD<Integer, Character> approxSample = data.sampleByKey(false, fractions);
      // Get an exact sample from each stratum
      JavaPairRDD<Integer, Character> exactSample = data.sampleByKeyExact(false, fractions);
      // $example off$
  
      System.out.println("approxSample size is " + approxSample.collect().size());
      for (Tuple2<Integer, Character> t : approxSample.collect()) {
        System.out.println(t._1() + " " + t._2());
      }
  
      System.out.println("exactSample size is " + exactSample.collect().size());
      for (Tuple2<Integer, Character> t : exactSample.collect()) {
        System.out.println(t._1() + " " + t._2());
      }
  
      jsc.stop();
    }
  }
  