CODEWITHSUNDEEP
javaguavatreemap
r123454321
r123454321

Reputation: 3403

Google Guava TreeMultimap -- retrieve values based on sorted ordering?

I'm trying to implement something that requires sorting of values of a <Destination -> Quantity> map, such as:

<San Francisco -> 10, Seattle -> 20, LA -> 10}

The values are not necessarily distinct. I want to be able to retrieve the key/value pair with the largest and smallest value, similar to what a TreeMap is able to do with keys.

I found Google Guava's TreeMultimap, which is an implementation of Multimap whose keys and values are ordered by their natural ordering or by supplied comparators. The thing is, TreeMultimap doesn't seem to have any methods that let me retrieve key/value pairs based on the ordering of the keys or values, (like what pollFirstEntry(), for instance, does in TreeMap).

To this extent, I'm a little confused on how to make a TreeMultimap obtain this functionality. I feel like it should work, maybe it's just a matter of how I instantiate the object?

Upvotes: 2

Views: 2321

Answers (2)

Mark Peters
Mark Peters

Reputation: 81104

It's true that TreeMultimap does order values according to a value comparator, but that ordering is only relevant in relation to other values mapped to the same key. So, for example, if you had 

 a => 3
 a => 1
 b => 4
 b => 2

And you iterated through the entries(), you should get [(a, 1), (a, 3), (b, 2), (b, 4)]. Similarly if you iterated through the values(), you should get [1, 3, 2, 4] as it returns the values of a in order, then the values of b in order.

Getting the first or last key is simple though, as keySet() returns a NavigableSet, meaning you can call first() and last() on it.

Upvotes: 0

Louis Wasserman
Louis Wasserman

Reputation: 198211

TreeMultimap isn't going to support this in quite the way you're looking for, I'm fairly certain.

What you could do is a TreeMultimap<Integer, String> -- swapping the role of the keys and the values -- and then TreeMultimap.asMap().lastEntry() would get you a Map.Entry<Integer, Collection<String>>, corresponding to the greatest Integer and all the Strings associated with it.

The one thing definitely not supported by TreeMultimap is looking at the combined values for all keys as a single sorted collection. (You can look at them as an unsorted collection with values(), of course.)

Upvotes: 2

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