Java sort map by value with Stream

Question

I have seen most of the examples using Stream to sort a map by the value but most of them were using a slightly easy version than mine and did not work for my case.

There was this website for examples similar to my case but it did not work as well since it creates the "int cannot be dereferenced" error due to compareTo() function as it is not for comparing primitives.

I also tried using Comparator.comparing() but it had no effect on the sorting at all.

I have something like below;

Map<String, Person> sortedMap = sortPersonByValue(personMap);

public static Map<String, Person> sortPersonByValue(final Map<String, Person> regions) {

        return regions.entrySet()
                .stream()
                .sorted(((e1, e2) -> e1.getValue().getAge().compareTo(e2.getValue().getAge()))
                //.sorted(Comparator.comparing(e1 -> e1.getValue().getAge()))
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e1, LinkedHashMap::new));
}

I would appreciate it if someone could point out what I am doing wrong. Thanks

Your code seems to work, at least for me. What doesn't work for you? Could you possibly add an example input and your expected output and maybe your class Person? — Eritrean, Nov 18 '20 at 16:08
@Eritrean I was wondering if you have tried it with commenting out the Comparator version and uncommenting the getValue() version? — Cugomastik, Nov 18 '20 at 16:34
@Eritrean that worked for me. Thank you very much for your help. — Cugomastik, Nov 18 '20 at 17:03
@Eritrean Do you know how to have a reverse order in this case? — Cugomastik, Nov 18 '20 at 17:05
Just swap the order of e1 and e2 in the comparison: `.sorted((e1,e2) -> Integer.compare(e2.getValue().getAge(), e1.getValue().getAge()))` — Eritrean, Nov 18 '20 at 17:33

Eritrean · Accepted Answer · 2020-11-18T16:42:48.963

1

Assuming Age is an int type and you want to use Integer.compare(x,y) version:

return regions.entrySet()
            .stream()
            .sorted((e1,e2) -> Integer.compare(e1.getValue().getAge(), e2.getValue().getAge()))
            .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e1, LinkedHashMap::new));

edited Nov 18 '20 at 16:42

answered Nov 18 '20 at 16:37

Eritrean

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how is this code different from that in the question in terms of what shouldn't have worked with the latter? – Naman Nov 19 '20 at 09:33

Java sort map by value with Stream

1 Answers1