How to sort HashMap of arrays by integer key Java

Question

I have a HashMap of arrays of strings identified by integers as key. I want to sort this HashMap by keys.

My hashmap : HashMap<Integer, String[]> htab = new HashMap<>();

I tried the TreeMap solution but it doesn't have a compatible constructor of my values (String[]): Map<Integer, String> map = new TreeMap<Integer, String>((Comparator<? super Integer>) htab);

Example of a set of my HashMap:

21 : {"2","3","5","10","0"}

If the values are **arrays** of strings, use `Map = new TreeMap<>();` instead of `Map`. — Jesper, Nov 29 '16 at 10:30
Or you can use **LinkedHashMap** and sort the instance of LinkedHashMap. This is a sample for how to sort a LinkedHashMap by value and sort by keys is the same. [link](http://stackoverflow.com/questions/12184378/sorting-linkedhashmap) — Ming, Nov 29 '16 at 10:42

score 1 · Answer 1 · answered Nov 29 '16 at 10:54

You don't need the (Comparator<? super Integer>) part for your TreeMap. Also you have used String instead of String[] in your declaration. This code will work:

SortedMap<Integer, String[]> sortedMap = new TreeMap<Integer, String[]>(Htab);

Or alternatively you can declare Htab as a TreeMap instead of a HashMap to begin with.

Edo user1419293 · Answer 2 · 2016-11-29T11:00:42.467

0

If you want to sort the keys you may use a TreeSet or a TreeMap as follows. The keys are naturally sorted, i.e. the sorting is defined by the Integer class.

Map<Integer, String[]> map = new HashMap<>();

Set<Integer> naturallySortedKeys = new TreeSet<>(map.keySet());
Map<Integer, String[]> naturallySortedMap = new TreeMap<>(map);

edited Nov 29 '16 at 11:00

answered Nov 29 '16 at 10:54

Edo user1419293

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2
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They are looking for a sorted map not a sorted key set. – Eddie Curtis Nov 29 '16 at 10:55
thanks for pointing that out. I just edited my answer to provide both. – Edo user1419293 Nov 29 '16 at 11:02

score 0 · Answer 3 · answered Nov 29 '16 at 10:55

Just create the TreeMap with the HashMap as a parameter.

public void test() {
    Map<Integer, String[]> htab = new HashMap<>();
    String[] a = {"a", "3", "5", "10", "0"};
    htab.put(21, a);
    String[] b = {"b", "3", "5", "10", "0"};
    htab.put(210, b);
    String[] c = {"c", "3", "5", "10", "0"};
    htab.put(2, c);
    Map<Integer, String[]> sorted = new TreeMap<>(htab);
    System.out.println(htab);
    System.out.println(sorted);
}

score 0 · Answer 4 · answered Nov 29 '16 at 10:55

You can use a TreeMap as per the comment written by jesper.

    Map<Integer, String[]> map = new TreeMap<Integer, String[]>();
    map.put(21, new String[] {"abc","bcde", "regweger"});
    map.put(43, new String[] {"dbc","bgercde", "reggweer"});
    map.put(31, new String[] {"afbc","bcdrge", "rewgwger"});
    map.put(5, new String[] {"abgc","bcdee", "regwesgr"});
    map.put(98, new String[] {"abhhc","bc3gde", "regrer"});
    map.put(11, new String[] {"awqbc","bc33de", "frgeger"});

    System.out.println(map.toString());

You will find the to string prints out the elements in ascending order of key value.

How to sort HashMap of arrays by integer key Java

4 Answers4