Java sort HashMap by highest value, then lowest key

Question

Lets say I have a HashMap<Recipe, Integer> where Recipe is a class with 2 integer parameters. We can call them lemons and sugar. I want to get the key (which is a Recipe) in the HashMap that has the highest corresponding value. As a secondary sorting method, in case it contains multiple Recipes with the same value. It should return the Recipe with the sum of sugar and lemons that is the lowest.

eg.

HashMap<Recipe, Integer> recipes = new HashMap<>();
recipes.put(new Recipe(5, 3), 10); // 5 is lemons, 3 is sugar
recipes.put(new Recipe(8, 8), 15);
recipes.put(new Recipe(1, 2), 15);
Recipe bestRecipe - recipes.getBestRecipe();
// bestRecipe.getLemons() would be 1
// bestRecipe.getSugar() would be 2
// because it has the highest value (15) with the lowest sum of sugar and lemons (1+2=3)

How would I go about doing that? I know I can get the largest value with Collections.max(recipes.values()) but how would I find the largest value with the lowest sum of lemons and sugar?

Do your `Recipe` objects have equals and hashcode? What is the criteria of comparison? — Sid, Jun 08 '20 at 04:37
Just write a `Comparator` that compares `Map.Entry` objects according to your logic. — Robby Cornelissen, Jun 08 '20 at 04:38
You can use this answer: https://stackoverflow.com/a/4805676/259889 — Sid, Jun 08 '20 at 04:39

score 2 · Accepted Answer · answered Jun 08 '20 at 05:02

You can create a stream of the map entries and use the max method to get the max element sorted by a comparator.

The comparator logic is as follows:

It sorts by the map's value.
In case of a tie, it reverse sorts by the sum of lemons and sugars of a recipe. This means that the values would be sorted from greatest to lowest.

Optional<Recipe> bestRecipe = recipes.entrySet()
                .stream()
                .max(Comparator.comparingInt((Map.Entry<Recipe, Integer> e) -> e.getValue())
                        .thenComparing(e -> e.getKey().getSugar() + e.getKey().getLemons(), 
                            Comparator.reverseOrder()))
                .map(Map.Entry::getKey);

Thank you so much for taking the time to explain it – divadneb nahtan Jun 08 '20 at 05:13 — divadneb nahtan, Jun 08 '20 at 05:13

Eklavya · Answer 2 · 2020-06-08T05:11:32.350

1

You can stream the map and write your comparator for sorting then get the first element

recipes.entrySet().stream()
        .sorted((e1, e2) -> {
             int v = e2.getValue().compareTo(e1.getValue());
             if(v!=0) return v;
             Integer a = (e1.getKey().getLemons() + e1.getKey().getSuger());
             Integer b = (e2.getKey().getLemons() + e2.getKey().getSuger());
             return Integer.compare(a,b);
         })
        .map(Map.Entry::getKey)
        .findFirst().get();

edited Jun 08 '20 at 05:11

answered Jun 08 '20 at 04:55

Eklavya

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This one seems to return the exact opposite haha. Dont worry though, Robby Cornelissen's answer worked. For me, it seemed to return the lowest value and the sugar+lemons was 40, which was the highest – divadneb nahtan Jun 08 '20 at 05:10
@divadnebnahtan sorry by bad check now – Eklavya Jun 08 '20 at 05:11

Java sort HashMap by highest value, then lowest key

2 Answers2