Java sorting and HashMap

Question

I have a HashMap<String, Integer> How can I sort this data structure and keep the key-value mappings? I want to sort by VALUES not keys.

Collection<Integer> counts = tableFrequency.values();

But then I lose the key mappings. Or is there a better associative data-structure that I could have used instead of the HashMap?

Possible duplicate of http://stackoverflow.com/q/2864840/1332690 — Charles Menguy, Apr 16 '12 at 00:21

Jeffrey · Accepted Answer · 2012-04-16T00:24:17.387

6

To sort a Map by its values, you could grab its entrySet and sort that with a custom Comparator.

List<Entry<K,V>> sorted = new ArrayList<>(map.entrySet());
Collections.sort(sorted, new Comparator<Entry<K,V>>() {
    public int compare(Entry<K,V> o1, Entry<K,V> o2) {
        return o1.getValue().compareTo(o2.getValue());
    }
};

edited Apr 16 '12 at 00:24

answered Apr 16 '12 at 00:02

Jeffrey

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I want to sort by the Values not the keys. How will this work? – CodeKingPlusPlus Apr 16 '12 at 00:12
Do you know what data-structure I can use to sort by values? – CodeKingPlusPlus Apr 16 '12 at 00:16
What library is Entry defined in? – CodeKingPlusPlus Apr 16 '12 at 00:24
@CodeKingPlusPlus It looks like he statically imported Map.Entry. – Andrew T Finnell Apr 16 '12 at 00:24
@CodeKingPlusPlus It's a nested class of `java.util.Map`. – Jeffrey Apr 16 '12 at 00:25

score 2 · Answer 2 · answered Apr 16 '12 at 00:04

2

TreeMap keeps the elements in the order in wich you added them. It seems like a perfect answer for you.

Beware though, some actions will be way slower than with a HashMap, things such as searching...

answered Apr 16 '12 at 00:04

geenux

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No it doesn't, `TreeMap` will sort elements as you add them. – Jeffrey Apr 16 '12 at 00:05
I want to sort by the values not the keys – CodeKingPlusPlus Apr 16 '12 at 00:12

score 1 · Answer 3 · edited May 23 '17 at 10:27

1

The class TreeMap is what you want:

TreeMap treeMap = new TreeMap();

treeMap.put("One", new Integer(1));
treeMap.put("Two", new Integer(2));

Object obj = treeMap.get("Two");
System.out.println(obj);

It uses the compare() method to be able to sort elements.

Since your new question is about sorting by values, this is a duplicate of this post

edited May 23 '17 at 10:27

Community

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answered Apr 16 '12 at 00:04

Charles Menguy

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It seems to have sorted my keys, I want it to sort by the values – CodeKingPlusPlus Apr 16 '12 at 00:07
why the downvote? the original post didn't include any notion of sorting by value... – Charles Menguy Apr 16 '12 at 00:16

Java sorting and HashMap

3 Answers3

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