CODEWITHSUNDEEP
javaguavatreemaps
Dmytro D
Dmytro D

Reputation: 2584

How to sort Guava's MultiMap only by keys?

I have MultiMap from Guava library. I want to sort it only by keys. I have tried:

Multimap<String, MyObj> sortedMultiMap =
    TreeMultimap.create(Ordering.from(new Comparator<String>() {
        @Override
        public int compare(String lhs, String rhs) {
            //my comparison here
        }
    }), Ordering.natural());//i want not to sort values at all,MyObj doesn't implement Comparable
sortedMultiMap.putAll(notSortedMultiMap);

But as you can see, TreeMultiMap.create method has 2 arguments - comparators for keys and values. How i can sort MultiMap only by keys?

Upvotes: 5

Views: 4078

Answers (2)

gustf
gustf

Reputation: 2017

Update after answer from Louis Wasserman Even if my original answer solved the problem and answered the question I think this is the more elegant solution. 

Multimap<String, MyObj> multimap = 
    MultimapBuilder.treeKeys(/* you comparator here */).linkedListValues().build();

You can use Ordering.arbitrary() as the second argument, it does not require the objects to implement Comparable.

If insertion order is needed you can use something like

Multimap<String, MyObj> sortedMultiMap = Multimaps.newMultimap(
            Maps.<String, Collection<MyObj>>newTreeMap(/* your comparator here*/),
            Lists::newLinkedList);

Upvotes: 7

Louis Wasserman
Louis Wasserman

Reputation: 198163

Use MultimapBuilder:

 Multimap<String, MyObj> multimap = 
      MultimapBuilder.treeKeys().linkedListValues().build();

Upvotes: 8

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