Possible Duplicate:
How to sort a Map<Key, Value> on the values in Java?
I have a treemap<Integer,Float>. How can I sort the the map on float point number?
Is there any quick way? or I have to write the comparator for the map?
Asked
Active
Viewed 1,906 times
-1
-
1@OP: Take note of the caveats on the accepted answer of the duplicate question. There are a _lot_ of ways in which that solution doesn't work. – Louis Wasserman Dec 14 '12 at 18:42
2 Answers
5
In practice, you can't (correctly, reliably) sort a Map implementation by the values. (The implementations you might see claiming otherwise are hackish, unreliable, and behave really weirdly -- rejecting duplicate values, throwing exceptions on attempts to look at keys not in the map, getting unrecoverably corrupted if the backing map changes...)
Instead, sort the list of entries explicitly:
List<Map.Entry<Integer, Float>> list = new ArrayList<>(map.entrySet());
Collections.sort(list, new Comparator<Map.Entry<Integer, Float>>() {
public int compare(Map.Entry<Integer, Float> e1, Map.Entry<Integer, Float> e2){
return e1.getValue().compareTo(e2.getValue());
}
});
If you liked, you could then put this into a LinkedHashMap:
Map<Integer, Float> sortedMap = new LinkedHashMap<Integer, Float>();
for (Map.Entry<Integer, Float> entry : list) {
sortedMap.put(entry.getKey(), entry.getValue());
}
Louis Wasserman
- 191,574
- 25
- 345
- 413
-
I depends on what the OP is asking - the original map remains unsorted (wrt the values). – assylias Dec 14 '12 at 18:40
-
2As I said in my answer, there is no reliable implementation which would do so. – Louis Wasserman Dec 14 '12 at 18:40
2
Easiest solution might be to use LinkedHashMap instead, and sort it by values. See this: How to sort a LinkedHashMap by its value class's field?
