Sorting Parallel Arrays

Question

Beginner in Java using an old textbook and Head First: Java books to figure some stuff out.

I have three arrays all parallel. I need to be able to sort by Title, Author, or Page Count based on user selection. I can sort one using Arrays.sort() but I'm getting hung up on how to sort the other two arrays to correspond to the new sorted one.

Say I sort the BookTitle array, but I'm going to need to display the proper author and page count of its respective arrays and I'm stumped.

do
{
    entry = JOptionPane.showInputDialog(null,
                                        "Enter your sort preference: \n" +
                                        "T = Sort by TITLE\n" +
                                        "A = Sort by AUTHOR\n" +
                                        "P = Sort by PAGE Count");

    c = entry.charAt(0);

    switch (c)
    {
    case 't':
    case 'T':
        Arrays.sort(BookTitle);
        for (int x = 0; x < BookTitle.length; x++)
        {
            msg += ("Title: " + BookTitle[x] + "\n");
        }
        JOptionPane.showMessageDialog(null, msg);
        isValid = true;
        break;

    case 'a':
    case 'A':
        isValid = true;
        break;

    case 'p':
    case 'P':
        isValid = true;
        break;

    default:
        JOptionPane.showMessageDialog(null, "Invalid entry");
        break;
    }
} while (isValid == false);

Are they required to be parallel? Because the best way to do it is to have 1 array of objects, where each object contains the Title, Author, and Page Count. — VoidStar, Nov 11 '11 at 03:53
Put them all in one class. Sort the array of objects of that class. Or something like that; I don't know Java. See http://stackoverflow.com/questions/4018090/sorting-listclass-by-one-of-its-variable — Mateen Ulhaq, Nov 11 '11 at 03:56

score 1 · Answer 1 · edited May 23 '17 at 12:30

Adapted from this post by @ScottStanchfield: sorting List<Class> by one of its variable

public class Book {
    String author;
    String title;
    String pages;
}

Collections.sort(list, new Comparator<Book>() {
    public int compare(Book c1, Book c2) {
        if (c1.pages > c2.pages)
            return -1;
        if (c1.pages < c2.pages)
            return 1;
        return 0;
    }
});

Book[] books;
Collections.sort(books);

I don't know Java, so if you see any mistakes, please correct them!

score 1 · Answer 2 · edited Nov 11 '11 at 04:45

You can create one Class with all the three attributes Author, Title, Pages. And then you can create 3 comparators which will compare in terms of Author, Title and Pages independently. And then you can take user input T, A, P like what you are doing buy you have to sort the array with the corresponding comparators. Pseudo code would be like:

Case A :
    Arrays.sort(ComparatorA);

case T:
    Arrays.sort(ComparatorT);

case P:
    Arrays.sort(ComparatorP);

score 1 · Answer 3 · answered Mar 27 '12 at 12:56

1

public class SortUtils {
    public static void sort(long[] x, long[] y) {
        for (int i = 0; i < x.length; i++) {
            for (int j = i; j > 0 && x[j - 1] > x[j]; j--) {
                swap(x, j, j - 1);
                swap(y, j, j - 1);
            }
        }
    }

    private static void swap(long anArray[], int a, int b) {
        long t = anArray[a];
        anArray[a] = anArray[b];
        anArray[b] = t;
    }
}

answered Mar 27 '12 at 12:56

Alexander Ashitkin

51
3

It's usually a bad idea to implement bubble sort, but this seems especially true when working in a language that has sorting algorithms built-in (e.g. `Arrays.sort`)... – Michael McGowan Sep 14 '12 at 21:40

score 0 · Answer 4 · edited May 23 '17 at 12:15

First option is as above, chuck them into one class and make it comparable like Why should a Java class implement comparable?.

This only allows you to compare on one value, I think there is a way to choose what to sort on, but not that I know.

The other way... is to implement your own sort method. It can be a bit of work, but is probably good to do at least once so you can learn it. Insertion and selection sort are pretty easy to master, and the will allows you to move elements in each array in parallel.

UPDATE: As above you can have multiple compartors, check out this website as it seems to have everything you need.

Sorting Parallel Arrays

4 Answers4

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