我有流的流(这种格式不是我设置,不能改变).例如
Stream<String> doc1 = Stream.of("how","are","you","doing","doing");
Stream<String> doc2 = Stream.of("what","what","upto");
Stream<String> doc3 = Stream.of("how","how");
Stream<Stream<String>> docs = Stream.of(doc1,doc2,doc3);
我试图将其转换为Map< String,Multiset< Integer>>的结构. (或其对应的流,因为我想进一步处理),其中密钥字符串是单词本身,并且Multiset< Integer>表示每个文档中出现的字数(应排除0). Multiset是一个谷歌番石榴类(不是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中做什么好的方法？
我尝试使用flatMap,但内部Stream极大地限制了我的选择.
解决方法
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,you=[1,1]}