Remove duplicate values from HashMap in Java

Question

I have a map with duplicate values:

(\"A\", \"1\");
(\"B\", \"2\");
(\"C\", \"2\");
(\"D\", \"3\");
(\"E\", \"3\");

I would like to the map

Answer 1

This can be easily done by putting your hashmap into arraylist. This arraylist is of hashmap type.

ArrayList<HashMap<String, String>> mArrayList=new ArrayList<>();
HashMap<String, String> map=new HashMap<>();
map.put("1", "1");
        mArrayList.add(map);
        map=new HashMap<>();
        map.put("1", "1"); 
        mArrayList.add(map);
        map=new HashMap<>();
        map.put("1", "2");
        mArrayList.add(map);
        map=new HashMap<>();
        map.put("1", "3");
        mArrayList.add(map);
        map=new HashMap<>();
        map.put("1", "2");
        mArrayList.add(map);

for(int i=0;i<mArrayList.size();i++)
        {
            temp=mArrayList.get(i).get("1");
            for(int k=i+1;k<mArrayList.size();k++)
            {
                if(temp.equals(mArrayList.get(k).get("1")))
                {
                    mArrayList.remove(k); 
                } 
            }

        }

Now print your arraylist...all the duplicate values from the hashmap easily removed...This is the easiest way to remove duplicacy

Answer 2

public static void main(String[] args) {
    Map<String, String> map = new HashMap<>();
    map.put("A", "1");
    map.put("B", "2");
    map.put("C", "2");
    map.put("D", "3");
    map.put("E", "3");
    System.out.println("Initial Map : " + map);
    for (String s : new ConcurrentHashMap<>(map).keySet()) {
        String value = map.get(s);
        for (Map.Entry<String, String> ss : new ConcurrentHashMap<>(map)
                .entrySet()) {
            if (s != ss.getKey() && value == ss.getValue()) {
                map.remove(ss.getKey());
            }
        }
    }
    System.out.println("Final Map : " + map);
}

Answer 3

This will be helpful to remove duplicate values from map.

    Map<String, String> myMap = new TreeMap<String, String>();
    myMap.put("1", "One");
    myMap.put("2", "Two");
    myMap.put("3", "One");
    myMap.put("4", "Three");
    myMap.put("5", "Two");
    myMap.put("6", "Three");

    Set<String> mySet = new HashSet<String>();

    for (Iterator itr = myMap.entrySet().iterator(); itr.hasNext();)
    {
        Map.Entry<String, String> entrySet = (Map.Entry) itr.next();

        String value = entrySet.getValue();

        if (!mySet.add(value))
        {
            itr.remove();               
        }
    }

System.out.println("mymap :" + mymap);

Output:

mymap :{1=One, 2=Two, 4=Three}

Answer 4

ConcurrentModificationException happening,because you are removing from map

  if (value.equals(nextValue)) {
            map.remove(key);
        }

You have to remove from iterator

if (value.equals(nextValue)) {
            keyIter.remove(key);
        }

Coming to the duplicate entry issue,Its pretty simple :Find duplicate values in Java Map?