CODEWITHSUNDEEP
javatreemap
Dileep Perla
Dileep Perla

Reputation: 1865

How to get key and value of a TreeMap at particular index

I have a TreeMap with a set of 'Key and Value' pairs. How can I get both Key and Value at a particular Index of the TreeMap?

EDIT : @TO-ALL : Thanks. But I know how to implement it by using an extra ArrayList. I just thought is there any way to achieve this without using an extra ArrayList.

Upvotes: 21

Views: 81302

Answers (6)

Vineet Agarwal
Vineet Agarwal

Reputation: 59

This might be helpful 

TreeMap< String,Integer > ht=new TreeMap<>();

ht.put("12",1);
ht.put("22",2);
ht.put("32",3);
ht.put("42",4);
for(int i=0;i<ht.size();i++)
{
   System.out.println(new Vector(ht.keySet()).get(i));
   System.out.println(new Vector(ht.values()).get(i));
}

Upvotes: 1

R&#233;da
R&#233;da

Reputation: 371

here is an other option to get the key from a value :

Map<String, String> map = new HashMap<String, String>();
map.put("s1", "s1Val");
map.put("s2", "s2Val");
map.put("s3", "s3Val");

    // ex: "s2Val" -> return "s2"

int index = new ArrayList<String>(map.values()).indexOf("s2Val");
System.out.println(map.keySet().toArray()[index]); // -> return "s2"

Upvotes: -2

Booyah Johnson
Booyah Johnson

Reputation: 101

First off, I'm not sure why people here so frequently concern themselves about the validity of a question. There are numerous instances where people have seen fit to maintain an ArrayList in sorted order. Maintaining an ArrayList in sorted order is grossly inefficient for large lists.

The Entry nodes of the standard Java (Oracle) source distribution do not maintain the size of their descendant trees. Because of this, it is not possible to identify an element within the map by index without an inefficient sequential search.

I find this drawback so severe that I have written my own AVL map that can efficiently get elements by index and compute indexOf(E). Making this possible is as simple as maintaining the sizes each of the left and right branches of an Entry. There is some chance that the Glazedlists library has a searchable tree embedded it in somewhere. You may wish to review that.

Upvotes: 9

Chandra
Chandra

Reputation: 1337

If you really want to use TreeMap and get by position, you can use the following:

key => treemap.keySet().toArray()[0]
value => treemap.get(key);

OR (if you just want value) 

treemap.values().toArray()[0];

But I would suggest you use iterator, as in the above method, it needs to create array whenever you want to find (so not so efficient) and also you should be careful enough to make sure index don't go out of reach.

Upvotes: 27

Alexei Kaigorodov
Alexei Kaigorodov

Reputation: 13525

You can copy entry set in an array list and then get desired entry by index:

list=new ArrayList<Map.Entry<K,V>>(treeMap.entrySet());
Map.Entry<K,V>=list.get(index);

But a) copying takes O(N) time and b) when treeMap changes, the list become invalid.

Upvotes: 6

Jean-Christophe Fortin
Jean-Christophe Fortin

Reputation: 748

This might not be the best way but you'll be able to access your key/value at a particular index.

TreeMap<Object, Object> foo = new TreeMap<Object, Object>();
Object key = foo.keySet().toArray(new Object[foo.size()])[YOUR_INDEX];
Object value = foo.get(key);

Upvotes: 2

Related Questions