Inbuilt short method to get array of keys of Hashmap sorted by their values in Java

Question

Many questions have been asked in StackOverflow regarding sorting the Hashmap by key or value. Most of them are posted over many years. For example,this,this, and this. I am searching for any onliner method for sorting the Hashmap keys by their values and get the array of the sorted keys. In iOS, following line of code yields the same:

NSArray* sortedKeys = [myDictionary keysSortedByValueUsingSelector:@selector(compare:)]};

Here, if the NSDictionary myDictionary contains the following objects:

{
 S: 1;
 A: 5;
 N: 8;
 T: 2;
 O: 0;
}

Then the sortedKeys contains the following objects:

(N, A, T, S, O)

Is such method available in the latest Java? Shall I follow the lengthy solutions? A lengthy solution given here yields a sorted Hashmap (keys sorted by their respective values). Will the order of the sorted keys still persists if I extract the keys of this sorted Hashmap using keySet()? Thank you!

https://stackoverflow.com/a/22132422/829571 – assylias Aug 24 '18 at 08:08 — assylias, Aug 24 '18 at 08:08

assylias · Accepted Answer · 2018-08-24T08:21:27.130

2

Using streams, you can write:

List<String> keys = map.entrySet().stream()
                      .sorted(Entry.comparingByValue())
                      .map(Entry::getKey)
                      .collect(toList());

It's a bit longer than your iOS example but not that bad.

To get the list in reverse order, you can use a reverse order comparator:

.sorted(Collections.reverseOrder(Entry.comparingByValue()))

edited Aug 24 '18 at 08:21

answered Aug 24 '18 at 08:11

assylias

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you need to reverse it though since OP wants descending order. also technically they wanted an Array not a List – Patrick Parker Aug 24 '18 at 08:13
1

@PatrickParker they might want an array, but they should use a List in Java. – Kayaman Aug 24 '18 at 08:42

Inbuilt short method to get array of keys of Hashmap sorted by their values in Java

1 Answers1