spark 数据分析 分组取TopN

package com.swust.seltop;

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.api.java.function.FlatMapFunction;
import org.apache.spark.api.java.function.Function2;
import org.apache.spark.api.java.function.PairFunction;
import scala.Tuple2;

import java.util.*;

/**
 *
 * @author 雪瞳
 * @Slogan 时钟尚且前行，人怎能再此止步！
 * @Function 分组取TopN
 *
 */
public class SortTopN {
    public static void main(String[] args) {
        SparkConf conf = new SparkConf();
        conf.setMaster("local").setAppName("top");
        JavaSparkContext jsc = new JavaSparkContext(conf);
        jsc.setLogLevel("Error");

        String inputPath = "./data/top.txt";
        JavaRDD<String> input = jsc.textFile(inputPath,1);
        //top10类
        JavaPairRDD<String, Integer> pairRDD = input.mapToPair(new PairFunction<String, String, Integer>() {
            @Override
            public Tuple2<String, Integer> call(String line) throws Exception {
                // 14 cat1 cat1
                String[] splits = line.split(" ");
                Tuple2<String, Integer> tp = new Tuple2<>(splits[0]+"\t"+splits[1]+"\t"+splits[2], Integer.parseInt(splits[0]));
                return tp;
            }
        });
        //为每一个分区创建一个本地 top10列表
        JavaRDD<SortedMap<Integer, String>> singleTop10 = pairRDD.mapPartitions(new FlatMapFunction<Iterator<Tuple2<String, Integer>>, SortedMap<Integer, String>>() {
            @Override
            public Iterator<SortedMap<Integer, String>> call(Iterator<Tuple2<String, Integer>> iterator) throws Exception {
                SortedMap<Integer, String> top = new TreeMap<>();
                while (iterator.hasNext()) {
                    Tuple2<String, Integer> next = iterator.next();
                    top.put(next._2, next._1);
                    //保留正序前10
                    if (top.size() > 10) {
                        top.remove(top.firstKey());
                    }
                }
                List<SortedMap<Integer, String>> list = Collections.singletonList(top);
                return list.iterator();
            }
        });
        //收集所有本地的top10 列表
        List<SortedMap<Integer, String>> singleResult = singleTop10.collect();
        SortedMap<Integer,String> finalResult = new TreeMap<>();
        for (SortedMap<Integer, String> elements : singleResult){
            //遍历map并将数据存储到finalResult内
            Set<Map.Entry<Integer, String>> entries = elements.entrySet();
            for (Map.Entry<Integer,String> entry:entries){
                finalResult.put(entry.getKey(),entry.getValue());
            }

            if (finalResult.size()>10){
                finalResult.remove(finalResult.firstKey());
            }
        }
        //输出结果
        for (Map.Entry<Integer,String> entry : finalResult.entrySet()){
            System.err.println(entry.getKey()+"------"+entry.getValue());
        }
        // 替代方案 使用reduce进行数据迭代
        /*singleTop10.reduce(new Function2<SortedMap<Integer, String>, SortedMap<Integer, String>, SortedMap<Integer, String>>() {
            @Override
            public SortedMap<Integer, String> call(SortedMap<Integer, String> sm1, SortedMap<Integer, String> sm2) throws Exception {
                SortedMap<Integer,String> top10 = new TreeMap<>();
                for (Map.Entry<Integer,String> entry : sm1.entrySet()){
                    top10.put(entry.getKey(),entry.getValue());
                    if (top10.size()>10){
                        top10.remove(top10.firstKey());
                    }
                }
                for (Map.Entry<Integer,String> entry : sm2.entrySet()){
                    top10.put(entry.getKey(),entry.getValue());
                    if (top10.size()>10){
                        top10.remove(top10.firstKey());
                    }
                }
                return top10;
            }
        });*/

    }
}