Class for finding the median of a two-dimensional space

Question

I have a simple static class that it's purpose is given an RDD of Point to find the median of each dimension and return that as a new Point using Spark's reduce functions.

This is the class:

public class MedianPointFinder {

    public static Point findMedianPoint(JavaRDD<Point> points) {
        Point biggestPointByXDimension = points.reduce((a, b) -> getBiggestPointByXDimension(a, b));
        Point biggestPointByYDimension = points.reduce((a, b) -> getBiggestPointByYDimension(a, b));

        double xDimensionMedian = biggestPointByXDimension.getX() / 2.0;
        double yDimensionMedian = biggestPointByYDimension.getY() / 2.0;

        return new Point(xDimensionMedian, yDimensionMedian);
    }

    private static Point getBiggestPointByXDimension(Point first, Point second) {
        return first.getX() > second.getX() ? first : second;
    }

    private static Point getBiggestPointByYDimension(Point first, Point second) {
        return first.getY() > second.getY() ? first : second;
    }
}

Point class is a simple class for storing an (x, y) point.

My understanding of median is the middle element out of N elements if the N elements were sorted. You are finding the highest element and dividing its value by 2. Is that what you really meant to do? For example, given three x coordinates 1 2 9 I consider the median to be 2 not 4.5. — JS1
– JS1, Commented Nov 28, 2014 at 6:08

Gerold Broser · Accepted Answer · 2014-11-27 22:43:11Z

3

I guess your Point is not a java.awt.Point since that holds x and y as int and you're using double.

Why not getting rid of your Point class by making the "Finder" class itself a MedianPoint?

import java.awt.geom.Point2D;

public class MedianPoint extends Point2D.Double {

  public MedianPoint(JavaRDD<Point> points) {
    super(
      /* your x calculation */,
      /* your y calculation */
      );
  }

  private static Point2D.Double greaterByXOf(Point2D.Double p1, Point2D.Double p2) {
    // ...
  }

  private static Point2D.Double greaterByYOf(Point2D.Double p1, Point2D.Double p2) {
    // ...
  }

} // MedianPoint

edited Nov 27, 2014 at 22:43

answered Nov 26, 2014 at 1:29

Gerold Broser

1,2788 silver badges20 bronze badges

\$\begingroup\$ I do need my Point class for some methods that I have created in it that does not exist in Point2D but I guess what I could do is wrap Point2D with my Point class and then do MedianPoint extends Point. \$\endgroup\$

Aki K
– Aki K

2014-11-26 09:15:08 +00:00
Commented Nov 26, 2014 at 9:15
\$\begingroup\$ Are there other reasons why you have to stick to Point? Which make moving Point's methods into MedianPoint impossible? \$\endgroup\$

Gerold Broser
– Gerold Broser

2014-11-26 10:47:46 +00:00
Commented Nov 26, 2014 at 10:47
\$\begingroup\$ No, not really. I just have it for providing a limited API and adding some functionality. I have posted my revised Point class here codereview.stackexchange.com/questions/70902/… \$\endgroup\$

Aki K
– Aki K

2014-11-26 11:21:25 +00:00
Commented Nov 26, 2014 at 11:21

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