Solved

Sorting array of coordinates

Posted on 2008-10-19
4
2,053 Views
Last Modified: 2012-08-13
Hi, I have a collection of coordinates x, y (doubles) i.e. (3.4, 5.3), (3.0, 5.5), and so on...

I put them into an array and I need to sort them based on either coordinate. I need to use the sort method from the java.util.Arrays class.

I imported the class, created an array in which I put all my coordinate objects. I'm not sure how the Arrays.sort() method works. How do I go about sorting the array based on either coordinate (x or y).

Let's say that I have :

Coordinate [] myArray = {c1, c2, c3, c4, ...cn} where each c is a coordinate i.e c1 = (3.4, 5.5)

Once again I need to use the built in method in the Arrays class.

Would I have to do something like,
Arrays.sort(myArray.getX()) getX() gets the x cordinate
in order to sort all the coordinates in increasing order of the X coordinate?

Sorry if this seems a trivial question, but even when I create an array on int's (int [] myArray), and I do Arrays.sort(myArray), the code doesn't compile.

p.s. I need to use the Arrays.sort() method, no need to create my own implementation.
0
Comment
Question by:ubuntuguy
  • 2
  • 2
4 Comments
 
LVL 4

Accepted Solution

by:
petr_hlucin earned 500 total points
ID: 22753506
What you should do is use the following version of Sort:
static void sort(Object[] a, Comparator c);

The Comparator and Coordinate would be the following in your case.
class CoordinageComparator implements Comparator{
 
  public int compare(Coordinate coordinate1, Coordinate coordinate2) {
    return coordinate1.compareTo(cordinate2);
  }
}
 
class Coordinate {
  public double X;
  public double Y;
 
  public CompareTo(Coordinate c) {
    if (c.X < this.X)
      return -1;
    else if (c.X > this.X)
      return 1;
    else 
      return 0;
  }
}

Open in new window

0
 
LVL 1

Author Comment

by:ubuntuguy
ID: 22753744
Hmmm, I thought about doing it this way, but my method must run in O(nlogn) and this would run in O(n^2).  I know the Arrays.sort() runs in O(nlogn), but I'm unsure on how to implement it.
0
 
LVL 4

Expert Comment

by:petr_hlucin
ID: 22753807
IMHO this would run in O(n*log(n)) - CompareTo() runs in O(1) and Sort by itself runs in O(n*log(n)). If you think that sort with Comparator runs in O(n^2) you may write your own sort :-). No, seriously I'm almost sure that Sort with Comparator runs in O(n*log(n)) and therefore the following code together with the one posted with my previous post should solve your problem in O(n*log(n)).
Coordinate[] c = new Coordinate[50];
 
Arrays.Sort(c, new CoordinateComparator());

Open in new window

0
 
LVL 1

Author Closing Comment

by:ubuntuguy
ID: 31507638
thanks, you were right.  
0

Featured Post

Free Tool: Subnet Calculator

The subnet calculator helps you design networks by taking an IP address and network mask and returning information such as network, broadcast address, and host range.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
netstat -ano | find "8000" and taskkill /f /pid 2984 3 83
tomcat not starting 6 69
type mismatch (Object[] to double[] 4 33
Eclipse Java import and method not resolved 4 51
This was posted to the Netbeans forum a Feb, 2010 and I also sent it to Verisign. Who didn't help much in my struggles to get my application signed. ------------------------- Start The idea here is to target your cell phones with the correct…
When there is a disconnect between the intentions of their creator and the recipient, when algorithms go awry, they can have disastrous consequences.
Video by: Michael
Viewers learn about how to reduce the potential repetitiveness of coding in main by developing methods to perform specific tasks for their program. Additionally, objects are introduced for the purpose of learning how to call methods in Java. Define …
This theoretical tutorial explains exceptions, reasons for exceptions, different categories of exception and exception hierarchy.

830 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question