How to Remove Items/Entries with Specific Values from Map/HashMa

  • 时间：2020-09-07 12:13:31
  • 分类：网络文摘
  • 阅读：142 次
2091E060-120E-4C44-BAA3-7E4E0DF7BD55 How to Remove Items/Entries with Specific Values from Map/HashMap Object in Java? java programming languages

Java

In Java, you can usually remove items or entries with some specific value from Map or HashMap object using traditional method:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

public Map<String, String> removeItemByValue(Map<String, String> data, String value) {
  for (var key: data.keySet()) {
    if (data.get(key) == null) {
       data.remove(key);
    }
  }
  return data;
}
 
var data = new HashMap<String, String>();
data.put("a", "1");
data.put("b", "2");
data.put("c", "2");
removeItemByValue(data, null); 
// only prints a = 1
for (var key: data.keySet()) {
  System.out.println(key + "=" + data.get(key)); 
}
public Map<String, String> removeItemByValue(Map<String, String> data, String value) {
  for (var key: data.keySet()) {
    if (data.get(key) == null) {
       data.remove(key);
    }
  }
  return data;
}

var data = new HashMap<String, String>();
data.put("a", "1");
data.put("b", "2");
data.put("c", "2");
removeItemByValue(data, null); 
// only prints a = 1
for (var key: data.keySet()) {
  System.out.println(key + "=" + data.get(key)); 
}

A Better Map-Item Removal Approach via using values()

The values() method in Map object actually returns a Collection view of the valujes that are contained in the map object. And the remove object return null when the item is not existent anymore. Thefore, we can use the following modern 1-liner in Java to remove the items in a Map that have the specific value.

1
2
3
4

public Map<String, String> removeItemByValue(Map<String, String> data, String value) {
  while (data.values().remove(value)) ;
  return data;
}
public Map<String, String> removeItemByValue(Map<String, String> data, String value) {
  while (data.values().remove(value)) ;
  return data;
}

To double check and verify that items are actually removed:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

package com.helloacm;
 
import java.util.HashMap;
import java.util.Map;
 
public class Main {
    public static void main(String[] args) {
        var data = new HashMap<String, String>();
        data.put("a", "b");
        data.put("e", "2");
        data.put("f", "2");
        while (data.values().remove("2"));
        // prints "a"        
        for (Map.Entry<String, String> entry: data.entrySet()) {
            System.out.println(entry.getKey());
        }
    }
}
package com.helloacm;

import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        var data = new HashMap<String, String>();
        data.put("a", "b");
        data.put("e", "2");
        data.put("f", "2");
        while (data.values().remove("2"));
        // prints "a"        
        for (Map.Entry<String, String> entry: data.entrySet()) {
            System.out.println(entry.getKey());
        }
    }
}

–EOF (The Ultimate Computing & Technology Blog) —

推荐阅读：
第15届华杯赛决赛小学组试题解析二（A卷）　 为什么生活中有那么多圆柱体？　 石头的体积　 梅文鼎与抽屉原理　 人体上的尺子　 一道行程问题　 一道关于比的应用题　 画家达·芬奇与数学　 a与b成反比例，b与c成反比例，a与c成什么比例？　 如何计算玻璃瓶（啤酒瓶）的容积　
评论列表
添加评论