How do you numerically sort an arraylist with int+string entries

Question

I'm working on a leaderboard and my data is stored in an ArrayList as

int + " " + username

I've been trying to sort it to display.

public static void main (String[] args) throws java.lang.Exception
{

    List<String> leaderboard = new ArrayList<String>();

    leaderboard.add("11 John");
    leaderboard.add("23 annie");
    leaderboard.add("1 putin");
    leaderboard.add("101 king");
    Collections.sort(leaderboard);

    for(int i = 0; i < leaderboard.size(); i++) {   
        System.out.print(leaderboard.get(i));
        System.out.println();
    } 

}

Outputs an alphabetical sort:

1 putin
101 king
11 John
23 annie

when I need

1 putin
11 John
23 annie
101 king

and to finish it off I would use

Collections.reverse(leaderboard);

To display it as a high score chart.

Make custom objects with a number and name as instance attributes. — Malik Brahimi
– Malik Brahimi, Commented Jan 2, 2016 at 22:21

Mureinik · Accepted Answer · 2016-01-02 22:24:12Z

4

You could create a custom Comparator to treat the first part of the string numerically:

public class NumericalStringComparator implements Comparator<String> {
    @Override
    public int compare (String s1, String s2) {
        int i1 = Integer.parseInt(s1.split(" ")[0]);
        int i2 = Integer.parseInt(s2.split(" ")[0]);
        int cmp = Integer.compare(i1, i2);
        if (cmp != 0) {
            return cmp;
        }
        return s1.compareTo(s2);
    }
}

You could then use it to in a reversed order to sort your collection:

 Collections.sort(leaderboard, new NumericalStringComparator().reversed());

answered Jan 2, 2016 at 22:24

Mureinik

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2 Comments

user1028872 Over a year ago

Wow that was fast. Works flawlessly thanks a lot! Using his code I get the proper sort. Thanks. Will accept as answer after 5 minute cooldown. Appreciate it.

CosmicGiant Over a year ago

This is only if you need the data to be stored as Strings. You probably don't. The recommended solution is to either use a Map<String, Integer> (instead of the current List) to map names to their respective scores; or to create a custom object that effectivelly does the same "key-value" pairing. This is to avoid storing numbers as String (memory-inefficient) and having to parse them in/out of Strings (cpu-inefficient)

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