sort HashMap in reverse?

Question

So I came across this method which is able to sort HashMaps by value.

public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue(Map<K, V> map) {
        return map.entrySet()
                .stream()
                .sorted(Map.Entry.comparingByValue())
                .collect(Collectors.toMap(
                        Map.Entry::getKey,
                        Map.Entry::getValue,
                        (e1, e2) -> e1,
                        LinkedHashMap::new
                        ));
    }

I want to use the reversed() method on the Comparator but I can't seem to find the right place to put it.

@LewBloch .sorted(Map.Entry.comparingByValue().reversed()) does not compile. Mureinik's solution works — Ben Arnao, Mar 01 '17 at 16:09

score 11 · Accepted Answer · answered Mar 01 '17 at 15:03

11

The reversed() method should be called on the Comparator returned by comparingByValue(). Java's type inference breaks down here, unfortunately, so you'll have to specify the generic types:

public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue
    (Map<K, V> map) {

    return map.entrySet()
            .stream()
            .sorted(Map.Entry.<K, V> comparingByValue().reversed())
            // Type here -----^ reversed() here -------^
            .collect(Collectors.toMap(
                    Map.Entry::getKey,
                    Map.Entry::getValue,
                    (e1, e2) -> e1,
                    LinkedHashMap::new
            ));
}

answered Mar 01 '17 at 15:03

Mureinik

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@BenArnao Which is exactly why it's generally a good idea to include what you've tried in your question as well as clear descriptions of why what you tried hasn't worked. – Jason C Mar 01 '17 at 15:07
2

Thanks, this is what i needed. I tried using reversed() at that place but it didn't work because i had to specify the type. – Ben Arnao Mar 01 '17 at 15:07

sort HashMap in reverse?

1 Answers1

Linked