在Java8中从数据流中提取Map<K、Multiset<V>>

import com.google.common.collect.Multiset;
import com.google.common.collect.Multisets;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Main {
    public static void main(String[] args) {
        // 假设我们有一个包含对象的数据流
        Stream<Pair<String, Integer>> stream = Stream.of(
                new Pair<>("A", 1),
                new Pair<>("B", 2),
                new Pair<>("A", 3),
                new Pair<>("C", 4),
                new Pair<>("B", 5)
        );

        // 将数据流转换为键值对流
        Stream<Pair<String, Pair<String, Integer>>> pairStream = stream.map(obj -> new Pair<>(obj.getKey(), obj));

        // 按照键进行分组
        Map<String, List<Pair<String, Pair<String, Integer>>>> groupedMap = pairStream.collect(Collectors.groupingBy(Pair::getKey));

        // 将值转换为Multiset
        Map<String, Multiset<Integer>> multisetMap = groupedMap.entrySet().stream()
                .collect(Collectors.toMap(Map.Entry::getKey, entry -> {
                    List<Pair<String, Pair<String, Integer>>> pairs = entry.getValue();
                    List<Integer> values = pairs.stream().map(Pair::getValue).map(Pair::getValue).collect(Collectors.toList());
                    return Multisets.copyHighestCountFirst(Multisets.newMultiset(values));
                }));

        // 输出结果
        multisetMap.forEach((key, multiset) -> System.out.println(key + ": " + multiset));
    }

    static class Pair<K, V> {
        private final K key;
        private final V value;

        public Pair(K key, V value) {
            this.key = key;
            this.value = value;
        }

        public K getKey() {
            return key;
        }

        public V getValue() {
            return value;
        }
    }
}

A: [3 x 1, 1 x 1]
B: [5 x 1, 2 x 1]
C: [4 x 1]