Java - 获取对象的arrayList中最常见的元素

Question

我有一个如下所示的ArrayList:

ArrayList<TravelData> listOfTravels;

和TravelData对象包含以下元素

int id;
String groupName;
String guideName;

这就是我初始化 arrayList 的方式:

listOfTravels.add(new TravelData(1,"group a", "Ross"));
listOfTravels.add(new TravelData(2,"group a", "Chandler"));
listOfTravels.add(new TravelData(3,"group a", "Monica"));
listOfTravels.add(new TravelData(4,"group b", "Phoebe"));
listOfTravels.add(new TravelData(5,"group b", "Rachel"));
listOfTravels.add(new TravelData(6,"group c", "Joey"));
listOfTravels.add(new TravelData(7,"group c", "Rachel"));
listOfTravels.add(new TravelData(8,"group d", "Chandler"));

我想要获取该列表中前 3 个最常见的组和指南。在此示例中:

Top 3 groups: "group a", "group b", "group c"
Top 3 guides: "Rachel", "Chandler", "Ross"

(第三名的导游可能是其他任何人，因为罗斯、莫妮卡、菲比和乔伊的出场次数相同)。

我找到了很好的答案，例如 how to get the most common element in a list但它仅适用于整数的ArrayList，并且仅显示第一个最常见的元素。

Answer 1

试试这个，它会对你有帮助。

public class TravelData {
int id;
String groupName;
public String getGroupName() {
    return groupName;
}

public String getGuideName() {
    return guideName;
}

String guideName;

public TravelData(int id, String groupName, String guideName) {
    this.id = id;
    this.groupName = groupName;
    this.guideName = guideName;
}

public static void getcommonGroups(ArrayList<TravelData>  list){
    Map<String, Integer> wordMap = new HashMap<String, Integer>();

    for(TravelData td:list){
        if(wordMap.containsKey(td.getGroupName())){
            wordMap.put(td.getGroupName(), wordMap.get(td.getGroupName())+1);
        } else {
            wordMap.put(td.getGroupName(), 1);
        }
    }

    List<Map.Entry<String, Integer>> sortedList = sortByValue(wordMap);
    for(Map.Entry<String, Integer> entry:sortedList){
        System.out.println(entry.getKey()+" ===="+entry.getValue());
    } }

  public static List<Map.Entry<String, Integer>> sortByValue(Map<String, Integer> 
  wordMap)  {

    Set<Map.Entry<String, Integer>> set = wordMap.entrySet();
    List<Map.Entry<String, Integer>> list = new ArrayList<Map.Entry<String, Integer>>(set);
    Collections.sort( list, new Comparator<Map.Entry<String, Integer>>()
    {
        public int compare( Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2 )
        {
            return (o2.getValue()).compareTo( o1.getValue() );
        }
    } );
    return list;
}


public static  void main(String args[]){
    ArrayList<TravelData> listOfTravels=new ArrayList() ;
    listOfTravels.add(new TravelData(1,"group a", "Ross"));
    listOfTravels.add(new TravelData(2,"group a", "Chandler"));
    listOfTravels.add(new TravelData(3,"group a", "Monica"));
    listOfTravels.add(new TravelData(4,"group b", "Phoebe"));
    listOfTravels.add(new TravelData(5,"group b", "Rachel"));
    listOfTravels.add(new TravelData(6,"group c", "Joey"));
    listOfTravels.add(new TravelData(7,"group c", "Rachel"));
    listOfTravels.add(new TravelData(8,"group d", "Chandler"));
    getcommonGroups(listOfTravels);
}}