Sort Map elements in java Map<String, List<String>> in reverseorder

Question

In my java program, i am getting result like

Output:

acre care race

act cat

Expected:

act cat

acre care race

Now I want to sort the Map elements in reverse order. So I can get the result like above. I added my code in below.

public static void main(String args[]) {

    try {
        Scanner sc = readWords();
        Map<String, List<String>> wordAnagramPairs = new HashMap<>();
        wordAnagramPairs = mapAnagrams(sc);
        Comparator<List<String>> c = (l1, l2) -> {
            Collections.sort(l1);
            Collections.sort(l2);
            int in = l1.get(0).length() - l2.get(0).length();
            if (in == 0) {
                return String.join(" ", l1).compareTo(String.join(" ", l2));
            } else {
                return in;
            }
        };
        List<List<String>> sortedList = wordAnagramPairs.values()
                .stream()
                .filter(li -> li != null && li.size() > 1)
                .sorted(c)
                .collect(Collectors.toList());

        for(List<String> anagrams : sortedList){
            for(String anagram : anagrams){
                System.out.print(anagram + " ");
            }
            System.out.print('\n');
        }

    } catch (FileNotFoundException e) {
        System.out.println("File Not Found");
    }
}

Use TreeMap instead of HashMap

Raghav
– Raghav

2016-11-13 05:04:57 +00:00
Commented Nov 13, 2016 at 5:04 — Raghav
– Raghav, Commented Nov 13, 2016 at 5:04

Saravana · Accepted Answer · 2016-11-13 11:01:44Z

1

By looking at your expected output, it seems you need to sort by length of the list element and then by the sorted list elements if the length is equal

To compare by element length and then list elements

Comparator<List<String>> c = (l1, l2) -> {
            Collections.sort(l1); // elements to be sorted
            Collections.sort(l2); // elements to be sorted
            int in = l1.get(0).length() - l2.get(0).length();
            if (in == 0) {
                return String.join(" ", l1).compareTo(String.join(" ", l2));
            } else {
                return in;
            }
        };

Since you want only the values to be printed you can use stream on values

    Map<String, List<String>> wordAnagramPairs = new HashMap<>();
    wordAnagramPairs.put("race", Arrays.asList("race", "care", "acre"));
    wordAnagramPairs.put("act", Arrays.asList("act", "cat"));
    wordAnagramPairs.values().stream()
                             .filter(li -> li != null && li.size() > 1)
                             .sorted(c)
                             .forEach(System.out::println);

Output

[act, cat]
[acre, care, race]

To collect the sorted results

    List<List<String>> sortedList = wordAnagramPairs.values().stream().filter(li -> li != null && li.size() > 1).sorted(c)
            .collect(Collectors.toList());

    System.out.println(sortedList);

You can also use TreeMap<String, TreeSet<String>> to sort the map by key and sort the values by Set value

To sort by key

    wordAnagramPairs.entrySet()
                    .stream()
                    .filter(e -> e.getValue().size() > 1)
                    .sorted(Map.Entry.comparingByKey())
                    .forEach(System.out::println);

edited Nov 13, 2016 at 11:01

answered Nov 13, 2016 at 5:10

Saravana

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8 Comments

Mohammad Shahadat Hossain Over a year ago

I tried both solution but still not working. It is same result.

Saravana Over a year ago

Did you try the first comparator? See the output, it matches your expected output.

Saravana Over a year ago

add all inputs in the Question, also mention which one is not working

Mohammad Shahadat Hossain Over a year ago

excellent, the comparator one i tried it's seems to be working. But if i remove .forEach(System.out::println); the result changes. Can you tell why is this happening?

Saravana Over a year ago

forEach is a terminal operation, stream to work we need should have terminal operator. added a collect to collect the sorted list. check updated answer with collect

|

Chandana Kumara · Accepted Answer · 2016-11-13 06:03:09Z

1

You can use TreeMap for this without use HashMap. Refer this :http://beginnersbook.com/2014/07/how-to-iterate-treemap-in-reverse-order-in-java/

Unless try as this:

To sort Map:

Map<String, List<String>> sortedMap = new TreeMap<String, List<String>>(Collections.reverseOrder());
sortedMap .putAll(wordAnagramPairs );

To sort List:
You can sort list inside for loop calling following one before iterate it.

Collections.sort(list, Collections.reverseOrder());

OR

Collections.reverse(list);

edited Nov 13, 2016 at 6:03

answered Nov 13, 2016 at 5:52

Chandana Kumara

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