Sorting a matrix or 2d array by the content of a column

Question

I'm looking for some help with the code to sort a matrix content by the content of one column, but keeping the data of the same row... I will try to show an example:

The initial matrix is:

1 - Martha - 12321 - 18

2 - Adam - 54345 - 22

3 - June - 76577 - 12

4 - Thomas - 23454 - 16

5 - Peter - 62356 - 24

As you can see, the first column is the position, second is the name, third is an imaginary ID, and fourth is the age of the person.

This is a String array, so numerical data is converted using String.valueOf(number);

Now, I would like to get help with the code to sort each row, by the content of any column.

For example, rows sorted by the names column, should be something like:

2 - Adam - 54345 - 22

3 - June - 76577 - 12

1 - Martha - 12321 - 18

5 - Peter - 62356 - 24

4 - Thomas - 23454 - 16

Now, rows sorted by the ID column, should be something like:

1 - Martha - 12321 - 18

4 - Thomas - 23454 - 16

2 - Adam - 54345 - 22

5 - Peter - 62356 - 24

3 - June - 76577 - 12

As you can see, the complete row was moved, instead of just the items in a single column.

May someone help me? Thanks in advance.

Answer 1

In c# you can make model for that specific type of array and then you can use lambda to sort it.
Exp. OrderBy(p=> p.Name)

Answer 2

Here's a quick solution using Comparator and Collections. Everything it should be self explanatory. Every field is a String, but you could easily use integer as well. Hope you find it useful.

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class MatrixCompare {

    public static void main(String[] args) {

        List<Contact> contacts = new ArrayList<Contact>();
        contacts.add(new Contact("1", "John", "456456", "35"));
        contacts.add(new Contact("2", "Jack", "123123", "20"));
        contacts.add(new Contact("3", "Mary", "234234", "24"));
        contacts.add(new Contact("4", "Jane", "345345", "18"));

        System.out.println("Initial List\n");
        printContacts(contacts);

        System.out.println("\n\nSorted by Id\n");
        Collections.sort(contacts, new SortById());
        printContacts(contacts);

        System.out.println("\n\nSorted by Name\n");
        Collections.sort(contacts, new SortByName());
        printContacts(contacts);

        System.out.println("\n\nSorted by Person Id\n");
        Collections.sort(contacts, new SortByPersonId());
        printContacts(contacts);

        System.out.println("\n\nSorted by Age\n");
        Collections.sort(contacts, new SortByAge());
        printContacts(contacts);

    }

    private static void printContacts(List<Contact> contacts) {
        for (int i=0; i<contacts.size(); i++) {
            System.out.println(contacts.get(i).id + " - " + contacts.get(i).name + " - " + 
                    contacts.get(i).getPersonId() + " - " + contacts.get(i).getAge());
        }
    }

    private static class Contact {

        String id;
        String name;
        String personId;
        String age;

        public Contact(String id, String name, String personId, String age) {
            this.id = id;
            this.name = name;
            this.personId = personId;
            this.age = age;
        }

        public String getId() {
            return id;
        }

        public String getName() {
            return name;
        }

        public String getPersonId() {
            return personId;
        }

        public String getAge() {
            return age;
        }

    }

    private static class SortById implements Comparator<Contact> {
        @Override
        public int compare(Contact o1, Contact o2) {
            String name1 = o1.getId();
            String name2 = o2.getId();  
            return name1.compareTo(name2);
        }
    }
    private static class SortByName implements Comparator<Contact> {
        @Override
        public int compare(Contact o1, Contact o2) {
            String name1 = o1.getName();
            String name2 = o2.getName();    
            return name1.compareTo(name2);
        }
    }
    private static class SortByPersonId implements Comparator<Contact> {
        @Override
        public int compare(Contact o1, Contact o2) {
            String name1 = o1.getPersonId();
            String name2 = o2.getPersonId();    
            return name1.compareTo(name2);
        }
    }
    private static class SortByAge implements Comparator<Contact> {
        @Override
        public int compare(Contact o1, Contact o2) {
            String name1 = o1.getAge();
            String name2 = o2.getAge(); 
            return name1.compareTo(name2);
        }
    }

}

Answer 3

Since a 2D array is actually an array of arrays, you sort the outer array using a custom Comparator<String[]> by calling Arrays.sort(array, comparator).