通过组合键值从哈希图中删除键

Question

Hey guys currently have problem with regards to removing duplicates from hashmap.

Some background:

My hashmap is in this format Map<CompositeKeyBean,ValueBean> .

CompositeKeyBean is in the form (String ID, String hashvalue) ;

ValueBean is an object.

So if i have a hashmap with values as such:

(ID:1,HashValue:123),Obj1
(ID:1,HashValue:234),Obj1
(ID:1,HashValue:345),Obj1

I need to remove the duplicate keys and only have items with unique IDs. currently I have come up with this, But it does not seem to work, im pretty sure i am doing something wrong.

for (Map.Entry<CompositeKeyBean, ReportDataBean> entry : list.entrySet())
    {
        String idvalue = entry.getKey().getCompositeKeyList().get(0);
        for(int i = 1; i < list.size();i++)
        {
            if(list.keySet().contains(idvalue))
            {
                list.remove(i);
            }
        }
    }

Answer 1

If you are expecting duplicate keys, then you can do the following way to handle it while populating the map itself:

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

if(map.containsKey("ID")){
String oldValue = map.get("ID");
//put logic to merge the value
}else{
map.put("ID","newValue");
}

Answer 2

My solution for this one would be to declare first an another Map which will be used to hold the number of times that a certain key has appeared in the original Map. For the second time, you can iterate the same map entrySet and remove the duplicates using the declared additional Map as reference.

Map<String, Integer> numberOfInstanceMap = new HashMap<String, Integer>(); //temporary placeholder

for (Map.Entry<CompositeKeyBean, ReportDataBean> entry : list.entrySet())
{
    String idvalue = entry.getKey().getCompositeKeyList().get(0);
    if(!numberOfInstanceMap.containsKey(idvalue)) {
        numberOfInstanceMap.put(idvalue, 1); //initialize the key to 1
    } else {
        numberOfInstanceMap.replace(idValue, numberOfInstanceMap.get(idValue) + 1); //add 1 to the existing value of the key
    }
}

for (Map.Entry<CompositeKeyBean, ReportDataBean> entry : list.entrySet())
{
    String idvalue = entry.getKey().getCompositeKeyList().get(0);
    Integer i = numberOfInstanceMap.get(idValue);
    if(i>1) { //remove duplicate if the key exists more than once
        list.remove(idValue);
    }        
}