根据成员字段的值在另一个列表中的位置对列表进行排序

Question

我有一个 Person 字段，包括 score(int)、name(String) 和 country(String)

1, Jane , Spain
2, James, Italy
1, John , Italy
2, Peter , England
3, Thomas , England
3, Martin , England

现在我提供另一个代表国家名称的字符串列表：[Italy, Spain, Norway, England, Germany]

我的要求是首先根据分数对人员列表进行排序，如果他们具有相同的分数然后按照国家名称列表中提供的国家名称进行排序。如果国家/地区名称也匹配，则按人名排序。

所以最后应该按这个顺序返回 person 对象：

1, John, Italy
1, Jane, Spain
2, James, Italy
2, Peter, England
3, Martin, England
3, Thomas, England

这是我正在尝试的代码：

public static List<Person> sortRecords(List<Person> people, List<String> countries) {
    people.sort((p1, p2) -> {
        int compare = p1.getScore() - p2.getScore();
        if(compare == 0) {
            compare = // how to compare by country names based on provided List<String> countries
            if(compare == 0) {
                compare = p1.getName().compareTo(p2.getName());
            }
        }
        return compare;
    });
}

我一直在按国家/地区名称进行比较。

Answer 1

使用List.indexOf

public static List<Person> sortRecords(List<Person> people, List<String> countries) {
    people.sort((p1, p2) -> {
        int compare = p1.getScore() - p2.getScore();
        if(compare == 0) {
            compare = countries.indexOf(p1.getCountry()) - countries.indexOf(p2.getCountry());
            if(compare == 0) {
                compare = p1.getName().compareTo(p2.getName());
            }
        }
        return compare;
    });
    return people;
}

---

请注意，由于排序是就地完成的，您不需要返回列表，然后使用java.util.Comparator 可以做一些好事

public static void sortRecords(List<Person> people, List<String> countries) {
    people.sort(
         Comparator.comparingInt(Person::getScore)
                   .thenComparingInt(person -> countries.indexOf(person.getCountry()))
                   .thenComparing(Person::getName)
    );
}

Answer 2

我会使用稳定的排序算法按名称、国家/地区和分数对列表进行排序。见https://www.geeksforgeeks.org/stability-in-sorting-algorithms/

import java.util.*;
class Record {
    int score; String name; String country;
    Record(int s, String n, String c){ score=s; name=n; country=c; }
    public String toString(){ 
      return String.format("[%d, %s, %s]", score, name, country);
    }
}
public class Main{
    public static void main(String[] args) {
        Record[] records = {
              new Record(1, "Jane" ,   "Spain"),
              new Record(2, "James",   "Italy"),
              new Record(1, "John" ,   "Italy"),
              new Record(2, "Peter",   "England"),
              new Record(3, "Thomas",  "England"),
              new Record(3, "Martin", "England")
        };
        Comparator<Record> byScore   = (r1,r2)->r1.score-r2.score;
        Comparator<Record> byCountry = (r1,r2)->r1.country.compareTo(r2.country);
        Comparator<Record> byName    = (r1,r2)->r1.name.compareTo(r2.name);

        System.out.println("===before====");
        Arrays.stream(records).forEach(System.out::println);
        
        Arrays.sort(records, byName); 
        Arrays.sort(records, byCountry);     
        Arrays.sort(records, byScore);
        
        System.out.println("===after====");
        Arrays.stream(records).forEach(System.out::println);
    }
}

输出

===before====
[1, Jane, Spain]
[2, James, Italy]
[1, John, Italy]
[2, Peter, England]
[3, Thomas, England]
[3, Martin, England]
===after====
[1, John, Italy]
[1, Jane, Spain]
[2, Peter, England]
[2, James, Italy]
[3, Martin, England]
[3, Thomas, England]