问题描述
如果解决方案非常明显,请原谅我,但我似乎不知道该怎么做
Forgive me if the solution is very obvious but I can't seem to figure out how to do this
public static void main(String[] args) {
Map<String, String> map = new HashMap<>();
map.put("b1", "a1");
map.put("b2", "a2");
map.put("b3", "a1");
Map<String, List<String>> mm = map.values().stream().collect(Collectors.groupingBy(m -> m));
System.out.println(mm);
}
我想基于哈希图中的值进行分组.我希望输出为{a1=[b1, b3], a2=[b2]}
,但当前为{a1=[a1, a1], a2=[a2]}
I want to group by based on values in hashmap. I want the output to be {a1=[b1, b3], a2=[b2]}
but it is currently coming as {a1=[a1, a1], a2=[a2]}
推荐答案
当前,您正在对地图值进行流式处理(我认为这是一个错字),根据所需的输出,您应该在地图上进行流式处理entrySet
并使用基于地图值的groupingBy
和mapping
作为基于地图键的下游收集器:
Currently, you're streaming over the map values (which I assume is a typo), based on your required output you should stream over the map entrySet
and use groupingBy
based on the map value's and mapping
as a downstream collector based on the map key's:
Map<String, List<String>> result = map.entrySet()
.stream()
.collect(Collectors.groupingBy(Map.Entry::getValue,
Collectors.mapping(Map.Entry::getKey,
Collectors.toList())));
您还可以通过forEach
+ computeIfAbsent
在没有流的情况下执行此逻辑:
You could also perform this logic without a stream via forEach
+ computeIfAbsent
:
Map<String, List<String>> result = new HashMap<>();
map.forEach((k, v) -> result.computeIfAbsent(v, x -> new ArrayList<>()).add(k));
这篇关于Map< String,List< String>的Collectors.groupby;的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!