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List集合按某個屬性或者字段進(jìn)行分組的操作

更新時間：2021年06月08日 14:16:10 作者：有趣的靈魂_不世俗的心

這篇文章主要介紹了List集合按某個屬性或者字段進(jìn)行分組的操作，具有很好的參考價值，希望對大家有所幫助。如有錯誤或未考慮完全的地方，望不吝賜教

List集合按某個屬性或者字段進(jìn)行分組

List<Object>分組按照Student對象中的Institution（學(xué)院）屬性進(jìn)行分組統(tǒng)計

核心代碼

Map<String, List<Student>> collect = stuList.stream().collect(Collectors.groupingBy(Student::getInstitution));

實現(xiàn)代碼示例：

public static void main(String[] args) {
  List<Student> stuList=initStuList2();
  Map<String, List<Student>> collect = stuList.stream().collect(Collectors.groupingBy(Student::getInstitution));
  for(String key:collect.keySet()){
   System.out.println(key+":" +collect.get(key).size());
   System.out.println(collect.get(key));
  }
 }
 
 public static  List<Student> initStuList2(){
  List<Student> stuList=new ArrayList<Student>(1000);
  for(int i=0;i<10;i++){ 
   Student student = new Student();
   long stu=(long) ((Math.random()*9+10000)*1000000);
   String Idcard=String.valueOf(stu).substring(0, 9);
   String ids=UUID.randomUUID().toString().replaceAll("-","");
   student.setId(ids);
   student.setUsername("student"+i);
   student.setClasses("計算機(jī)"+i);
   student.setIdcard("362425199"+Idcard);
   String [] institution={"信息學(xué)院","文學(xué)院","音樂學(xué)院","體院","理學(xué)院","機(jī)電學(xué)院"};
   int ss=(int)(Math.random()*6);
   student.setInstitution(institution[ss]);
   student.setMobile("18179"+Idcard.substring(0, 6));
   student.setEmail(Idcard+"@qq.com");
   student.setQq(Idcard);
   student.setHomeaddress("廣東省深圳市");
   student.setWeixin(Idcard);
   if(i%50==0){student.setSex("廣東省深圳市");}
   else{
    String[] sexs={"男","女"};
    int ii=((int) Math.random());
    student.setSex(sexs[ii]); 
   }
   student.setCreateby("拿破侖");
   student.setCreatetime(new Date());
   stuList.add(student);
  }
  return stuList;
 }

實現(xiàn)效果

按照學(xué)院分組，得到體院集合中6個對象，文學(xué)院2個對象，理學(xué)院1個對象，信息學(xué)院1個對象

List<Map<String,Object>>分組統(tǒng)計根據(jù)性別分類

核心代碼：

Map<String, List<Map<String, Object>>> gslist = agentList.stream().collect(Collectors.groupingBy(e -> e.get("sex").toString()));

實現(xiàn)代碼示例

public static void main(String[] args) {
		List<Map<String,Object>> agentList=init();
		HashMap<String, Object> hashMap =(HashMap<String, Object>) agentList.get(0);
		Map<String, List<Map<String, Object>>> gslist = agentList.stream().collect(Collectors.groupingBy(e -> e.get("sex").toString()));
		for(String key:gslist.keySet()){
	    	System.out.println(key+" : "+gslist.get(key).size());
	    	System.out.println(gslist.get(key));
	    }
	}
 	
	/***
	 * 初始化聯(lián)系信�?
	 * @return
	 */
	public static  List<Map<String,Object>> init(){
		String insertID=UUID.randomUUID().toString().replaceAll("-","");
		List<Map<String,Object>> concacts= new ArrayList<Map<String,Object>>();
		long time1=System.currentTimeMillis();
		for(int i=0;i<10;i++){
			String id=UUID.randomUUID().toString().replaceAll("-","");
			Map<String, Object> map = new HashMap<String,Object>();
			map.put("id", id);
			map.put("name", "張三");
			map.put("identity_no", "36242519961225"+(int)(Math.random()*10000+1000));
			map.put("telphone","1852562"+(int)(Math.random()*10000+1000));
			map.put("address","江西吉安");
			map.put("levels", "VIP");
			map.put("source", 0);
			map.put("flight_no", "ZH9101");
			map.put("planned_takeofftime", "1220");
			map.put("estimated_takeofftime", "1425");
			map.put("flight_change_type", 1);
			map.put("flight_change_reason", "軍事活動");
			map.put("flightdate","2019-05-01");
			map.put("en_name", "ZHANG/SAN");
			map.put("traveller_idx", (int)(Math.random()*1000+100));
			String [] sexs={"男","女","同性戀","人妖"};
			int kk=(int) (Math.random()*4);
			map.put("sex", sexs[kk]);
			map.put("phone_num","1302880"+(int)(Math.random()*10000+1000));
			map.put("originating", "SZX");
			map.put("terminus", "BKK");
			map.put("ticketid", (int)(Math.random()*10000+1000));
			map.put("mainspace", "J");
			map.put("sonspace", "C");
			map.put("message_info", "4");
			map.put("extension", "1892562"+(int)(Math.random()*10000+1000));
			map.put("officeid", (int)(Math.random()*10000+1000));
			map.put("pnrics", (int)(Math.random()*10000+1000));
			map.put("traveller_safe", "2019-02-23 ZH9007");
			map.put("phone_inform", 1);
			concacts.add(map);
		}
		long time2=System.currentTimeMillis();
		//System.out.println("初始化數(shù)據(jù)花�?"+(time2-time1)/1000);
		return concacts;
	}

實現(xiàn)效果

List分組的兩種方式

java8之前List分組

假設(shè)有個student類，有id、name、score屬性，list集合中存放所有學(xué)生信息，現(xiàn)在要根據(jù)學(xué)生姓名進(jìn)行分組。

public Map<String, List<Student>> groupList(List<Student> students) {
 Map<String, List<Student>> map = new Hash<>();
 for (Student student : students) {
  List<Student> tmpList = map.get(student.getName());
  if (tmpList == null) {
   tmpList = new ArrayList<>();
   tmpList.add(student);
   map.put(student.getName(), tmpList);
  } else {
   tmpList.add(student);
  }
 }
 return map;
}

java8的List分組

public Map<String, List<Student>> groupList(List<Student> students) {
 Map<String, List<Student>> map = students.stream().collect(Collectors.groupingBy(Student::getName));
 return map;
}

以上為個人經(jīng)驗，希望能給大家一個參考，也希望大家多多支持腳本之家。

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