How to remove duplicates from Hashmap of type HashMap<String, Object>?

Question

I'm having haspmap of type <String, Object>. This hashmap contains the duplicates entries. I'm trying the below method to remove the duplicates. But its showing an error. Please find the code and error as below.

This is the original hashmap which contains data.

Map<String , Object> map = new HashMap<String , Object>();

I'm trying to add the values to sets.

Set<String> valueSet = new HashSet<String>(map.values());

In the map.values() its showing an error saying that cannot resolve the constructor hashset(java.util.collection)

After this I'm adding the below code to eliminate the duplicates.

Iterator<String> it = valueSet.iterator();

        Map<Integer , String> uniqueMap = new HashMap<Integer , String>();

        while(it.hasNext()){
            String value = it.next();

            for(Entry<Integer , String> e : map.entrySet()){
                if(value.equals(e.getValue())  && !uniqueMap.containsValue(value)){
                    uniqueMap.put(e.getKey(), value);
                }
            }
        }

But due the error, I'm not able to proceed further. Could you please help me where I'm doing wrong. Thank you.

A Map cannot have duplicate keys, but maybe duplicate values. If what you want/need is to have both unique keys and values/ you can use a BiMap from Google Guava's library or use this algorithm: 1) create a new map, 2) for each key/value pair in your original map, store them in the new map using the value as key and the key as value 3) store the values from the new map back in the old map — Luiggi Mendoza
– Luiggi Mendoza, Commented Jan 14, 2016 at 3:09

Titus · Accepted Answer · 2016-01-14 04:57:23Z

5

This:

Map<String , Object> map = new HashMap<String , Object>();
Set<String> valueSet = new HashSet<String>(map.values());

Doesn't work because map.values() returns a Collection<Object> and the set is of type String.

Try this:

Map<String , Object> map = new HashMap<String , Object>();
Set<Object> valueSet = new HashSet<Object>(map.values());

Or:

Map<String , String> map = new HashMap<String , String>();
Set<String> valueSet = new HashSet<String>(map.values());

@coders in response to your comment, if you have a list of maps and you want to create a set of this maps's unique values, you can do this:

ArrayList<HashMap<String, Object>> mDataList = new ArrayList<HashMap<String, Object>>();
Set<Object> valueSet = new HashSet<Object>();  
for(HashMap<String, Object> map : mDataList){
    valuesSet.addAll(map.values());
}

edited Jan 14, 2016 at 4:57

answered Jan 14, 2016 at 3:10

Titus

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4 Comments

coders Over a year ago

Hello @Titus, how to loop through the list of hashmap<string, object> to eliminate the duplicates. Ex: ArrayList<HashMap<String, Object>> mDataList = new ArrayList<HashMap<String, Object>>();

Titus Over a year ago

@coders what do you mean by duplicates ? maps with the same entries or multiple maps having the same key or the same value ?

coders Over a year ago

Thanks, But how can you add this(<HashMap<String, Object> map : mDataList) inside the for loop. Thats not correct right?

Titus Over a year ago

@coders that was a typo, it had an < at the start that shouldn't have been there.

Naitik · Accepted Answer · 2016-01-14 03:21:33Z

2

Hasmap cannot store duplicate keys.

answered Jan 14, 2016 at 3:21

Naitik

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