Sort two-dimensional array with strings-CodePudding

I'm trying to sort this array by the last name, and if two last names are the same, I want to sort it by the first name:

String[][] phoneBook = { 
    /* name,                number */ 
    {"Sophia Thorarensen", "06508641036"}, 
    {"Emma Blöndal",       "06504228512"}, 
    {"Olivia Thorarensen", "06501126965"}, 
    {"Ava Hansen",         "06762858077"}
};

What it should look like:

String[][] sortedPhoneBook = { 
    /* name,                number */ 
    {"Emma Blöndal",       "06504228512"}, 
    {"Ava Hansen",         "06762858077"}, 
    {"Olivia Thorarensen", "06501126965"}, 
    {"Sophia Thorarensen", "06508641036"}
};

CodePudding user response：

This was a good exercise to try.

The idea is you need to use the sort method and then implement a custom Comparator based on your needs.

Here is one way I managed to do this according to the useful links provided by OH GOD SPIDERS.

I also think the sort happens in place so I did not create a new variable. I just printed out the contents of the old phoneBook at the end to show they are in the order we want.

import java.util.Arrays;
import java.util.Comparator;

public class SortStrings {

    public static void main(String[] args) {
    String[][] phoneBook = {
            /* name, number */
            { "Sophia Thorarensen", "06508641036" }, { "Emma Blöndal", "06504228512" },
            { "Olivia Thorarensen", "06501126965" }, { "Ava Hansen", "06762858077" } };

    Arrays.sort(phoneBook, new Comparator<String[]>() {
        public int compare(String[] a, String[] b) {
        
        //get first names and last names of what we want to compare.
        String first_name_a = a[0].split(" ")[0];
        String first_name_b = b[0].split(" ")[0];

        String last_name_a = a[0].split(" ")[1];
        String last_name_b = b[0].split(" ")[1];

        //if the last names are the same, sort by first name
        if (last_name_a.compareTo(last_name_b) == 0) {
            return first_name_a.compareTo(first_name_b);
        }

        return last_name_a.compareTo(last_name_b);

        }
    });

    Arrays.stream(phoneBook)
          .forEach(elem -> {
              Arrays.stream(elem)
                    .forEach(System.out::println);
          });

    }

}

Output:

CodePudding user response：

In general, it is better to build a Comparator instance. To write a clean code, you should split your comparator into two parts: sort by the first name, sort by the last name.

The final comparator should be built based on simple ones using thenComparing().

public static void sort(String[][] phoneBook) {
    final Comparator<String[]> sortByFirstName = (one, two) -> {
        String lastName1 = one[0].substring(0, one[0].indexOf(' ')).trim();
        String lastName2 = two[0].substring(0, two[0].indexOf(' ')).trim();
        return lastName1.compareTo(lastName2);
    };
    final Comparator<String[]> sortByLastName = (one, two) -> {
        String lastName1 = one[0].substring(one[0].lastIndexOf(' ')).trim();
        String lastName2 = two[0].substring(two[0].lastIndexOf(' ')).trim();
        return lastName1.compareTo(lastName2);
    };
    final Comparator<String[]> sortByLastNameAndFirstName =
                        sortByLastName.thenComparing(sortByFirstName);

    Arrays.sort(phoneBook, sortByLastNameAndFirstName);
}