aggregateByKeyStatCounter.java

import org.apache.spark.SparkConf;
import org.apache.spark.api.java.JavaPairRDD;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.JavaSparkContext;
import org.apache.spark.util.StatCounter;
import scala.Tuple2;
import scala.Tuple3;

import java.util.Arrays;
import java.util.List;

public class AggregateByKeyStatCounter {

    public static void main(String[] args) {
        SparkConf conf = new SparkConf().setAppName("AggregateByKeyStatCounter).setMaster("local");
        JavaSparkContext sc = new JavaSparkContext(conf);

        List<Tuple2<String, Integer>> myList = Arrays.asList(new Tuple2<>("A", 8), new Tuple2<>("B", 3), new Tuple2<>("C", 5),
                new Tuple2<>("A", 2), new Tuple2<>("B", 8));

        JavaRDD<Tuple2<String, Integer>> data = sc.parallelize(myList);
        JavaPairRDD<String, Integer> pairs = JavaPairRDD.fromJavaRDD(data);

        JavaRDD<Tuple3<String, Double, Double>> output = pairs.aggregateByKey(new StatCounter(), StatCounter::merge, StatCounter::merge).map(x -> new Tuple3<String, Double, Double>(x._1(), x._2().stdev(), x._2().mean()));

        output.collect().forEach(System.out::println);
    }

}