CODEWITHSUNDEEP
javasortingguavamultimap
oko
oko

Reputation: 1355

How to sort Guava MultiMap by count of values for each key

I already saw this question and answer here, but my use case is doing it at creation process.

I can create a multimap like that :

ImmutableListMultimap<Foo, Bar> indexMultiMap = Multimaps.index(barCollection, new Function<Bar, Foo>() {
     @Override
     public Foo apply(Bar bar) {
        //some works
        return Foo;
     }
  });

I know that Foo elements will be unique, and i want to sort this map by frequency of each Foo element size of Bar collection of each Foo element) in this map, descending.

1) How can i do that with one iteration ? Like doing it when indexing this collection to MultiMap

2) If not so, what is the efficient way to get it ?

My objective is at all, when i am iterating this map, i want to see first key has the bigger count of values, like

Foo -> 3 (size of bar collection corresponding to this key)

Foo -> 3

Foo -> 2

Foo -> 1

Foo -> 1

Upvotes: 3

Views: 1530

Answers (2)

hakunami
hakunami

Reputation: 2441

As @px5x2 said. when you call Multimaps.index(), keys appear in the order they are first encountered. So, sort your collection first. Using the Guava Multimaps.index() example here with tiny modification.

ImmutableSet<String> digits = ImmutableSet.of("zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine");
Function<String, Integer> lengthFunction = new Function<String, Integer>(){
    public Integer apply(String input) {
        return input.length();
    }
};
ImmutableMultimap<Integer, String> sortedOnLength = Multimaps.index(
    Ordering.natural().onResultOf(lengthFunction).sortedCopy(digits), 
    lengthFunction
);

Upvotes: 2

px5x2
px5x2

Reputation: 1565

From javadoc of Multimaps.index();

"In the returned multimap, keys appear in the order they are first encountered ..."

If the collection is sorted in a way that 'simulates' implicit sorting behaviour, multimap will be created in the order you want. eg:

SortedMultiset preSorted = TreeMultiset.create(fooComparator);

then feed Multimaps.index() with above preSorted collection.

Upvotes: 1

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