Sort map on value?

Question

if i have a map like this:

Map<Fruit, Double> multiMap = new HashMap<Fruit, Double>();

is there a way for me to sort on the Double values while still keeping the Double values linked to the corresponding Fruit object?

initially i was thinking of doing something like this:

public ArrayList<Double> sortAllValues() {
    ArrayList<Double> allEntries = new ArrayList<Double>();

    for (Entry<Fruit, Double> entry : multiMap.entrySet())
        allEntries.add(entry.getValue());
    }
return Collections.sort(allEntries);
}

but if i do this i lose the linkage between the Fruit and the Double value... any ideas?

Thanks in advance

Hashtables do not store any order and are not intended for keeping inorder data — Cruncher, Mar 19 '13 at 15:34
Perhaps you want an array of fruit, and sort them by the double that they map to. — Cruncher, Mar 19 '13 at 15:34
Looks like it's exactly what you need: http://stackoverflow.com/questions/109383/how-to-sort-a-mapkey-value-on-the-values-in-java — BobTheBuilder, Mar 19 '13 at 15:36
It looks like you just want to sort the values as oppose to the keys. This has been answered before like @baraky pointed out. http://stackoverflow.com/questions/109383/how-to-sort-a-mapkey-value-on-the-values-in-java — Franklin, Mar 19 '13 at 15:45
Are you sure you want to use a Map? Why not bring the double into your Fruit class so it is always together? — Aboutblank, Mar 19 '13 at 15:47
Can you give a before-and-after example of what your multimap would look like before and after sorting? It's not at all clear what kind of sorting you want. — Louis Wasserman, Mar 19 '13 at 16:12

score 2 · Accepted Answer · answered Mar 19 '13 at 15:55

2

consider the following:

class ValuedFruit implements Comparable<ValuedFruit> {
    private Fruit fruit;
    private double value;

    @Override
    public int compareTo(ValuedFruit o) {
        return (value < o.value) ? -1 : ((value > o.value) ? 1 : 0);
    }
}
List<ValuedFruit> fruits = new ArrayList<ValuedFruit>();
void sort(List<ValuedFruit> fruits){
    Collections.sort(fruits);
}

answered Mar 19 '13 at 15:55

BlackJoker

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The compareTo method could just contain `return Double.compare(this.value, o.value)`, which would have the bonus of not breaking the ordering if any value happens to be NaN. – VGR Mar 20 '13 at 12:40

Subhrajyoti Majumder · Answer 2 · 2013-03-19T15:52:30.847

1

It is not possible that you can maintain order of map entries(key,value) based on the value but it could possible based on key with TreeMap<k,v>.

TreeMap is sorted according to the natural ordering of its keys, or by a Comparator provided at map creation time, depending on which constructor is used. This implementation provides guaranteed log(n) time cost for the containsKey, get, put and remove operations.

What you could possibly do that is update your code -

public ArrayList<Double> sortAllValues() {    
     return Collections.sort(multiMap.values());
}

It will stop unnecessary iteration.

edited Mar 19 '13 at 15:52

answered Mar 19 '13 at 15:38

Subhrajyoti Majumder

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for some reason, your answer looks very odd + this sentence made no sense whatsoever to me. **There is no way where you can sort map entry(key,value) on based on value but based on value it is possible with TreeMap** – Rahul Mar 19 '13 at 15:44
http://stackoverflow.com/questions/109383/how-to-sort-a-mapkey-value-on-the-values-in-java – Franklin Mar 19 '13 at 15:46
Thanks for commenting I have updated it – Subhrajyoti Majumder Mar 19 '13 at 15:53

score 1 · Answer 3 · answered Mar 19 '13 at 15:47

You just have single double value associated with every Fruit object. If this is the case then sorting doesn't make any sense. If you have multiple double values associated with a single Fruit object then change the structure of your map to something like this :

Map<Fruit, Set<Double>> multiMap = new HashMap<Fruit, Set<Double>>();

You can use TreeSet, to keep the values sorted.

Sort map on value?

3 Answers3