Sorting Maps

[Shasi Sekar]

Hi All,

I have a doubt on sorting a map

i explain the steps i followed.

1. put the keys and values in different collections
2.sort the values
3.iterate through sorted values,then iterate through the key set.
4.get the value from the unsorted map w.r.t to the key iteration
5.compare the value with the iterated value.
6.put the key and value into a sorted map if the comparison succeeds.

when i print the key an value after the successful comparison, i get the out put as required,i.e the output is sorted w.r.t. values.
but when the same output is inserted into a sorted map. I get the output as sorted w.r.t. keys.


what am i missing here.Is there a map which give the output in first in first out pattern


I code is below

public class SortMaps {

	HashMap<String, String> jumbledMap = new HashMap<String, String>();
	SortedMap<String,String>  sortingMap = new TreeMap<String,String>() ;
	
	public SortMaps() {
	}

	public HashMap addMapObjects(){
		jumbledMap.put("Abbas", "Chennai");
		jumbledMap.put("Alex", "Ooty");
		jumbledMap.put("Ajay", "Karumpalam");
		jumbledMap.put("Bharath", "Chennai");
		jumbledMap.put("Baskar", "Salem");
		jumbledMap.put("Parthi", "Salem");
		jumbledMap.put("Gates", "Bangalore");
		jumbledMap.put("Naveen", "Bangalore");
		jumbledMap.put("Saravanan", "Karumpalam");
		jumbledMap.put("Anand", "Ooty");
		
		System.out.println(jumbledMap.size()+"\t unsorted size ");
		return jumbledMap;
	}

	public void iterateMapKeys(SortedMap<String, String> sortedMap){

		Iterator keyItr = sortedMap.keySet().iterator();

		System.out.println("///////////////////////////////////");
		while(keyItr.hasNext()){
			String key = keyItr.next().toString();
			String value = sortedMap.get(key);
			
			System.out.println(key+"\t"+value);
		}
		System.out.println("///////////////////////////////////");
	}

	public SortedMap sortMap(HashMap map){

		
		//Keys and value are put into different collection
		Set  keys = map.keySet();
		LinkedList keyList = new LinkedList();
		LinkedList valueList = new LinkedList();

		Collection values =  map.values();
		keyList.addAll(keys);
		valueList.addAll(values);
		
		//Values are sorted
		Collections.sort(valueList);
		ListIterator valueItr = valueList.listIterator();
		String key="";
		String mapValue="";
		while(valueItr.hasNext()){
			String value = valueItr.next().toString();
			//compare the values from the sorted value list and the original hash map 
			//and put the key and value into the hash map if they are equal 
			Iterator itrKeys = keyList.iterator();
			while(itrKeys.hasNext()){
				key = itrKeys.next().toString();
				mapValue = map.get(key).toString();
				//to get the key for the selected value
				if(value.equals(mapValue)){
//					System.out.println(key+"\t" +mapValue); //Here The output is as expected
					sortingMap.put(key, mapValue);
					itrKeys.remove();
				}
			}
			valueItr.remove();
		}
		
		
		return sortingMap;
	}

	public static void main(String[] args) {

		SortMaps sortMaps = new SortMaps();
		HashMap unsorted = sortMaps.addMapObjects();
		SortedMap sorted = sortMaps.sortMap(unsorted); 
		sortMaps.iterateMapKeys(sorted);
	}
}

Regards,
Shasi Sekar

[Shasi Sekar]

i got it ... need to use linked hash map.

[Campbell Ritchie]

A linked hash map isn’t sorted; it is ordered. Sorted means you keep the keys from smallest to largest. A linked hash map keeps them from first inserted to last inserted. If you really want sorting, look for a Sorted Map and that link will give hints about which classes you can use.

[Shasi Sekar]

yes Ritchie, you are right.But i had sorted the values already using comparator and wanted a map with FIFO.

[Campbell Ritchie]

Maps don’t implement FIFO; lists do. But your linked hash map is a combination of a map and a list, so the list bit can implement FIFO for you.

[Shasi Sekar]

yes you are very right.That's what i have done

[Campbell Ritchie]

Shasi Sekar wrote:yes you are very right. . . .

Aww shucks, you’ve embarrassed me!

Well done getting it sorted out