从Java 8中的Stream of Stream中提取Map <K,Multiset <V >>

Question

我有流的字流(这种格式不是由我设定的,不能更改).对于前者

Stream<String> doc1 = Stream.of("how", "are", "you", "doing", "doing", "doing");
Stream<String> doc2 = Stream.of("what", "what", "you", "upto");
Stream<String> doc3 = Stream.of("how", "are", "what", "how");
Stream<Stream<String>> docs = Stream.of(doc1, doc2, doc3);

我试图把它变成一个结构Map<String, Multiset<Integer>>(或者它的相应流,因为我想进一步处理它),其中键String是单词本身,Multiset<Integer>代表每个文档中出现的单词的数量(应该排除0) .Multiset是google guava类(不是来自java.util.).

例如:

how   -> {1, 2}  // because it appears once in doc1, twice in doc3 and none in doc2(so doc2's count should not be included)
are   -> {1, 1}  // once in doc1 and once in doc3
you   -> {1, 1}  // once in doc1 and once in doc2
doing -> {3}     // thrice in doc3, none in others 
what  -> {2,1}   // so on
upto  -> {1}  

在Java 8中执行此操作的好方法是什么？

我尝试使用flatMap,但内部Stream大大限制了我的选项.

Answer 1

 Map<String, List<Long>> map = docs.flatMap(
            inner -> inner.collect(
                    Collectors.groupingBy(Function.identity(), Collectors.counting()))
                    .entrySet()
                    .stream())
            .collect(Collectors.groupingBy(
                    Entry::getKey,
                    Collectors.mapping(Entry::getValue, Collectors.toList())));

System.out.println(map);

// {upto=[1], how=[1, 2], doing=[3], what=[2, 1], are=[1, 1], you=[1, 1]}