2
我想按集合中出现在我的对象中的值作为列表进行分组。Java Stream - 按关键字出现在列表中时分组
这是模型,我有
public class Student {
String stud_id;
String stud_name;
List<String> stud_location = new ArrayList<>();
public Student(String stud_id, String stud_name, String... stud_location) {
this.stud_id = stud_id;
this.stud_name = stud_name;
this.stud_location.addAll(Arrays.asList(stud_location));
}
}
当我用下面的初始化:
List<Student> studlist = new ArrayList<Student>();
studlist.add(new Student("1726", "John", "New York","California"));
studlist.add(new Student("4321", "Max", "California"));
studlist.add(new Student("2234", "Andrew", "Los Angeles","California"));
studlist.add(new Student("5223", "Michael", "New York"));
studlist.add(new Student("7765", "Sam", "California"));
studlist.add(new Student("3442", "Mark", "New York"));
我希望得到以下几点:
California -> Student(1726),Student(4321),Student(2234),Student(7765)
New York -> Student(1726),Student(5223),Student(3442)
Los Angeles => Student(2234)
我试着写下如下
Map<Student, List<String>> x = studlist.stream()
.flatMap(student -> student.getStud_location().stream().map(loc -> new Tuple(loc, student)))
.collect(Collectors.groupingBy(y->y.getLocation(), mapping(Entry::getValue, toList())));
但是我无法完成它 - 如何在映射后保留原始学生?
它应该是'Map>'。此外,你还没有显示你的'Tuple'类,但我怀疑'Entry :: getValue'不是你想要的。我会去'y - > y.getStudent()'。它的作品:)。 –
Tunaki