问题描述
我有一个键作为字符串和值作为列表的映射.列表可以有 10 个唯一值.我需要将此映射转换为键为整数,值为列表.示例如下:
I have map with key as String and value as List. List can have 10 unique values. I need to convert this map with key as Integer and value as List. Example as below :
输入:
Key-1":1,2,3,4
"Key-1" : 1,2,3,4
Key-2":2,3,4,5
"Key-2" : 2,3,4,5
"Key-3" : 3,4,5,1
"Key-3" : 3,4,5,1
预期输出:
1 : "Key-1","Key-3"
1 : "Key-1","Key-3"
2 : "Key-1","Key-2"
2 : "Key-1","Key-2"
3 : "Key-1", "Key-2", "Key-3"
3 : "Key-1", "Key-2", "Key-3"
4 : "Key-1", "Key-2", "Key-3"
4 : "Key-1", "Key-2", "Key-3"
5 : "Key-2", "Key-3"
5 : "Key-2", "Key-3"
我知道使用 for 循环可以实现这一点,但我需要知道这可以通过 java8 中的流/lamda 来完成.
I am aware that using for loops i can achieve this but i needed to know can this be done via streams/lamda in java8.
-谢谢.
推荐答案
一个想法是从原始映射中生成所有值-键对,然后按这些值对键进行分组:
An idea could be to generate all value-key pairs from the original map and then group the keys by these values:
import java.util.AbstractMap.SimpleEntry;
import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.mapping;
import static java.util.stream.Collectors.toList;
...
Map<Integer, List<String>> transposeMap =
map.entrySet()
.stream()
.flatMap(e -> e.getValue().stream().map(i -> new SimpleEntry<>(i, e.getKey())))
.collect(groupingBy(Map.Entry::getKey, mapping(Map.Entry::getValue, toList())));
这篇关于Java8流:将值作为列表转置映射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!