CODEWITHSUNDEEP
javasortingdictionarycollectionsjava-stream
hotmeatballsoup
hotmeatballsoup

Reputation: 605

Converting Java map into ordered collection based on map values

Please note: I see that this question appears similar to this one but in that question, they are simply sorting a map. Here I need to extract keys and their values out of a map, sort them and place them, in order into another collection. And that collection must be streamable and present the elements of that stream in the order that the sorting method placed them in.

Java 11 here. I have the following POJO:

@Data // lombok generates ctor, getters, setters, etc.
public class Answer {
    private String text;
    // ... many other fields here, omitted for brevity
}

I have a Map<Answer,Integer> that represents the number of instances for each Answer, for example:

Map<Answer,Integer> answerCounts = new HashMap<>();
answerCounts.put(answer1, 14); // answer #1 occurs 14 times
answerCounts.put(answer2, 7);
answerCounts.put(answer3, 239);
answerCounts.put(answer4, 7);
answerCounts.put(answer5, 54);
answerCounts.put(answer6, 2);

I would like to convert this map into a collection (likely either a List or Set) where the Answer elements are ordered according to their count values in the map. In the case of "ties" (where two map keys have the same count value) then it doesn't really matter what order the Answer elements appear in, so long as they are sorted correctly according to other, non-tying elements.

So using the map example above, I'd like the output of this conversion to be a list/set that provides Answer elements in the following order:

  1. Answer #3 (count = 239)
  2. Answer #5 (count = 54)
  3. Answer #1 (count = 14)
  4. Answer #2 (count = 7)
  5. Answer #4 (count = 7) (<-- #2 and #4 have same count so their respective order doesn't matter to me)
  6. Answer #6 (count = 2)

Any idea how I could accomplish this? The objective is to have a collection that I can then stream over (someCollection.stream()...) and process elements in order of how they appear in the "counts map".

Upvotes: 0

Views: 1060

Answers (1)

AlexM28
AlexM28

Reputation: 71

Use a LinkedHashMap instead of a Map. The difference is that the first one has an order, so when you sort it it will remain sorted (until you modify or add new elements)

By the way, you can stream over a Map

answerCounts.entrySet()
  .stream()
  .sorted(Map.Entry.comparingByValue())
  .forEach(System.out::println);

This will sort the Map but in the wrong order, and i can't find a way to reverse it

Upvotes: 2

Related Questions