如何使用Java 8流将List <Object>转换为Map <String，List <String >>？

Question

我有一个Employee对象，它具有rowId，skillId和Student如下

[0, 20,"John"],

[1, 30,"Amy"],

[2, 20,"Tom"]

我需要这样的答复：

Map<skillId, List<student>>

20 , ["John","Tom"]

30 , [Amy]

有人可以帮忙吗？

Answer 1

尝试使用var dateGroups = periodQuery.Select(x => x.Date).Distinct().OrderBy(x => x.Date); //working var datesEx = dateGroups.Select(g => periodQuery.Where(x => g.Date == x.Date).FirstOrDefault()); //not working 和groupingBy

mapping

Answer 2

请使用以下内容，

Map<Integer, List<Employee>> collect = employeeList.stream()
                .collect(Collectors.groupingBy(Employee::getSkillId, Collectors.toList()));

Answer 3

Map<Integer, List<String>> skillAndList = list.stream().collect(Collectors.groupingBy(Employee::getSkillId, Collectors.mapping(Employee::getStudent, Collectors.toList())));
System.out.println(skillAndList);

输出与您预期的相同-

{30=[Amy], 20=[John,Tom]}