Question

我有流语言流（此格式不是我设置的，不能更改）。对于前

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我正在尝试将其转换为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);的结构（或其相应的流，因为我想进一步处理它），其中键Map<String, Multiset<Integer>>是单词本身和{{1表示每个文档中出现的单词的数量（应排除0）。 Multiset是一个google guava类（不是来自java.util。）。

例如：

String

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极大地限制了我的选项。

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]}

Answer 2

Map<String, Multiset<Integer>> result = docs
        .map(s -> s.collect(Collectors.toCollection(HashMultiset::create)))
        .flatMap(m -> m.entrySet().stream())
        .collect(Collectors.groupingBy(Multiset.Entry::getElement,
                Collectors.mapping(Multiset.Entry::getCount,
                        Collectors.toCollection(HashMultiset::create))));

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

Multiset对于获取字数非常有用，但对于存储计数并不是必需的。如果您对Map<String, List<Integer>>感到满意，只需将最后一行替换为Collectors.toList())));。

或者，既然您还在使用Guava，为什么不使用ListMultimap？

ListMultimap<String, Integer> result = docs
        .map(s -> s.collect(Collectors.toCollection(HashMultiset::create)))
        .flatMap(m -> m.entrySet().stream())
        .collect(ArrayListMultimap::create,
                (r, e) -> r.put(e.getElement(), e.getCount()),
                Multimap::putAll);

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

Answer 3

由于您使用的是Guava，因此您可以利用其实用程序来处理流。与Table结构相同。这是代码：

Table<String, Long, Long> result =
    Streams.mapWithIndex(docs, (doc, i) -> doc.map(word -> new SimpleEntry<>(word, i)))
        .flatMap(Function.identity())
        .collect(Tables.toTable(
            Entry::getKey, Entry::getValue, p -> 1L, Long::sum, HashBasedTable::create));

这里我使用Streams.mapWithIndex方法为每个内部流分配索引。在map函数中，我将每个单词转换为由单词和索引组成的对，以便我以后可以知道该单词属于哪个文档。

然后，我将所有文档的对(word, index)平面映射到一个流，最后，我通过{{3}将所有对收集到番石榴Table收集器。行是单词，列是文档（由索引表示），值是每个文档的单词计数（我为每个不同的1L对分配(word, index)并使用{ {1}}合并冲突）。

您拥有Long::sum表格中所需的所有信息，但如果您仍然需要result，则可以这样做：

Map<String, Multiset<Integer>>

注意：你需要Guava 21才能工作。

Answer 4

以下是AbacusUtil的简单解决方案：

Map<String, List<Integer>> m = Stream.of(doc1, doc2, doc3)
          .flatMap(d -> d.toMultiset().stream()).collect(Collectors.toMap2());

提取地图<k，multiset <v =“”>＆gt;来自Java 8中的Stream of Streams

4 个答案: