Sorting HashMap based on its Values

Hi, Can someone suggest me or send a code snippet to sort the HashMap based on its values(not the keys), so that when I display, I get the values in some sorted manner. Thanks & Regards, Vishal Reply to this Threaded Messages (11) Sorting HashMap based on its Values by Artem Yegorov on October 21 2004 12:22 EDT Close, but throws out ties by Tim Ringwood on March 31 2005 10:23 EST How about without LinkedHashMap by M J on October 03 2005 02:01 EDT Use TreeMap by Tray Alford on October 14 2005 10:58 EDT Solution - Use a List by Oluwafemi Adetula on December 14 2005 06:42 EST Correction by Oluwafemi Adetula on December 15 2005 12:12 EST Possible Enhancement by Alex Hill on March 16 2006 09:36 EST And Another Thing by Alex Hill on March 16 2006 09:38 EST re by jhon river on June 07 2010 11:41 EDT Re: Sorting Maps based on its values by Anders Eriksson on October 24 2004 18:27 EDT Re: Sorting Maps based on its values by Vishal Revankar on October 25 2004 06:03 EDT Sorting HashMap based on its Values[ Go to top ]Posted by: Artem Yegorov Posted on: October 21 2004 12:22 EDT in response to Mayank Bhargava Something like this, maybe? Map someMap= new LinkedHashMap(); someMap.put("key1","c"); someMap.put("key2","a"); someMap.put("key3","b"); List mapKeys = new ArrayList(someMap.keySet()); List mapValues = new ArrayList(someMap.values()); someMap.clear(); TreeSet sortedSet = new TreeSet(mapValues); Object[] sortedArray = sortedSet.toArray(); int size = sortedArray.length; //a) Ascending sort for (int i=0; i<size; i++) { //System.out.println(sortedArray[i]); someMap.put(mapKeys.get(mapValues.indexOf(sortedArray[i])), sortedArray[i]); } System.out.println(someMap); someMap.clear(); //b) Descending sort for (int i=size; i>0;) { someMap.put(mapKeys.get(mapValues.indexOf(sortedArray[--i])), sortedArray[i]); } System.out.println(someMap); Regards, Artem D. Yegorov http://www.activexml.org Reply to this Reply to original Close, but throws out ties[ Go to top ]Posted by: Tim Ringwood Posted on: March 31 2005 10:23 EST in response to Artem Yegorov That works if all the values are unique, which isn't true in my case. I ened up with the below. Maybe somebody can make it better, but it does deal with duplicate values. public LinkedHashMap sortHashMapByValues(HashMap passedMap, boolean ascending) { List mapKeys = new ArrayList(passedMap.keySet()); List mapValues = new ArrayList(passedMap.values()); Collections.sort(mapValues); Collections.sort(mapKeys); if (!ascending) Collections.reverse(mapValues); LinkedHashMap someMap = new LinkedHashMap(); Iterator valueIt = mapValues.iterator(); while (valueIt.hasNext()) { Object val = valueIt.next(); Iterator keyIt = mapKeys.iterator(); while (keyIt.hasNext()) { Object key = keyIt.next(); if (passedMap.get(key).toString().equals(val.toString())) { passedMap.remove(key); mapKeys.remove(key); someMap.put(key, val); break; } } } return someMap; } Reply to this Reply to original How about without LinkedHashMap[ Go to top ]Posted by: M J Posted on: October 03 2005 14:01 EDT in response to Tim Ringwood Any ideas on how to do this without using a LinkedHashMap? We're still on 1.3 which doesn't support LinkedHashMap and I'm not going to get the web admins to upgrade us anytime soon. Reply to this Reply to original Use TreeMap[ Go to top ]Posted by: Tray Alford Posted on: October 14 2005 10:58 EDT in response to M J I would look at the TreeMap that is available in 1.3 and look at implementing the comparable interfaces to the value objects or provide a comparator object. This should take care of all your probs. http://java.sun.com/j2se/1.3/docs/api/java/util/TreeMap.html Reply to this Reply to original Solution - Use a List[ Go to top ]Posted by: Oluwafemi Adetula Posted on: December 14 2005 18:42 EST in response to Tray Alford I had the same problem - could not sort a map based on values rather than keys. To solve this I simply created a list of objects, where each object wraps a Map.Entry and implements java.lang.Comparable. Here's the class: ----- import java.util.*; public class CustomEntry implements Comparable{ private Map.Entry entry; public CustomEntry(Map.Entry entry) { this.entry = entry; } public Map.Entry getEntry() { return this.entry; } public int compareTo(CombinationEntry anotherEntry) { Integer thisIntegerVal = (Integer)(this.getEntry().getValue()); int thisVal = thisIntegerVal.intValue(); Integer anotherIntegerVal = (Integer)(anotherEntry.getEntry().getValue()); int anotherVal = anotherIntegerVal.intValue(); return (thisVal<anotherVal ? 1 : (thisVal==anotherVal ? 0 : -1)); } public int compareTo(Object o) { return compareTo((CombinationEntry)o); } } ----- You first convert your map to a list of these custom entries (here's a method, which does this): ---------- public static List convertMapToList(Map map) { List list = new ArrayList(); Set entrySet = map.entrySet(); Iterator iterator = entrySet.iterator(); while (iterator.hasNext()) { Map.Entry entry = (Map.Entry)iterator.next(); CustomEntry customEntry = new CustomEntry(entry); list.add(customEntry); } return list; } ---------- Now you can sort the list produced from the above method by calling java.util.Collections.sort(List list). Unfortunately, what you are left with is not a map anymore but a list pretending to be a map! Reply to this Reply to original Correction[ Go to top ]Posted by: Oluwafemi Adetula Posted on: December 15 2005 12:12 EST in response to Oluwafemi Adetula In my previous post there were 2 errors - CombinationEntry should be CustomEntry. Here is the corrected version of my message: -------- I had the same problem - could not sort a map based on values rather than keys. To solve this I simply created a list of objects, where each object wraps a Map.Entry and implements java.lang.Comparable. Here's the class: ----- import java.util.*; public class CustomEntry implements Comparable{ private Map.Entry entry; public CustomEntry(Map.Entry entry) { this.entry = entry; } public Map.Entry getEntry() { return this.entry; } public int compareTo(CustomEntry anotherEntry) { Integer thisIntegerVal = (Integer)(this.getEntry().getValue()); int thisVal = thisIntegerVal.intValue(); Integer anotherIntegerVal = (Integer)(anotherEntry.getEntry().getValue()); int anotherVal = anotherIntegerVal.intValue(); return (thisVal<anotherVal ? 1 : (thisVal==anotherVal ? 0 : -1)); } public int compareTo(Object o) { return compareTo((CustomEntry)o); } } ----- You first convert your map to a list of these custom entries (here's a method, which does this): ---------- public static List convertMapToList(Map map) { List list = new ArrayList(); Set entrySet = map.entrySet(); Iterator iterator = entrySet.iterator(); while (iterator.hasNext()) { Map.Entry entry = (Map.Entry)iterator.next(); CustomEntry customEntry = new CustomEntry(entry); list.add(customEntry); } return list; } ---------- Now you can sort the list produced from the above method by calling java.util.Collections.sort(List list). Unfortunately, what you are left with is not a map anymore but a list pretending to be a map! Reply to this Reply to original Possible Enhancement[ Go to top ]Posted by: Alex Hill Posted on: March 16 2006 09:36 EST in response to Oluwafemi Adetula Along the same lines as Oluwafemi's. Using an annonymous inner class is a little cleaner perhaps. ---------------------------- Map<String, Integer> map = new HashMap<String, Integer>(); // --- Put entries into map here --- // Get a list of the entries in the map List<Map.Entry<String, Integer>> list = new Vector<Map.Entry<String, Integer>>(map.entrySet()); // Sort the list using an annonymous inner class implementing Comparator for the compare method java.util.Collections.sort(list, new Comparator<Map.Entry<String, Integer>>(){ public int compare(Map.Entry<String, Integer> entry, Map.Entry<String, Integer> entry1) { // Return 0 for a match, -1 for less than and +1 for more then return (entry.getValue().equals(entry1.getValue()) ? 0 : (entry.getValue() > entry1.getValue() ? 1 : -1)); } }); // Clear the map map.clear(); // Copy back the entries now in order for (Map.Entry<String, Integer> entry: list) { map.put(entry.getKey(), entry.getValue()); } Reply to this Reply to original And Another Thing[ Go to top ]Posted by: Alex Hill Posted on: March 16 2006 09:38 EST in response to Alex Hill Not sure that it's good practise to consider a Map as having an ordering at all. Reply to this Reply to original re[ Go to top ]Posted by: jhon river Posted on: June 07 2010 23:41 EDT in response to Tim Ringwood thanks, nice info about kelly used car|kelley book used car|black dining table|white table lamp|mahogany dining table|lucite coffee table Reply to this Reply to original Re: Sorting Maps based on its values[ Go to top ]Posted by: Anders Eriksson Posted on: October 24 2004 18:27 EDT in response to Mayank Bhargava If it doesn't have to be a 'Hash' map and if you're allowed to leverage some nice open source you may want to consider automaticly sorted maps like the TreeBidiMap (a SortedBidiMap) of Jakarta Commons Collections. Direct link to Javadoc http://jakarta.apache.org/commons/collections/apidocs-COLLECTIONS_3_1/org/apache/commons/collections/bidimap/TreeBidiMap.html Reply to this Reply to original Re: Sorting Maps based on its values[ Go to top ]Posted by: Vishal Revankar Posted on: October 25 2004 06:03 EDT in response to Anders Eriksson Thank You, Artem & Anders, That was of great help. Regards, Vishal Reply to this Reply to original