Find closest entries in a list by comparing with one entry

manpreet Best Answer 3 years ago

I have a Unit class which has lots of fields in it as shown below:

public class Unit {
  private final int id;
  private final int beds;
  private final String city;
  private final double lat;
  private final double lon;

  // constructors and getters here
  // toString method

}

I now have a List of Unit which is a List object which contains lots of Units. Now I need to find the nearest Units from List object to Unit x. Cap the results by limit.

  private List<Unit> nearestUnits(List<Unit> lists, Unit x, int limit) {
    List<Unit> output = new ArrayList<>();

    // how do I sort lists object in such a way so that I can get nearest units here to "x"?

    return output;
  }

We have lat/long present in the Unit class so we can use that to calculate euclidean distance and do the comparison. I am confused on how to sort the list of units by shortest distance and get the nearest units. I am working with Java 7 as of now so I can't use Java 8.

manpreet 3 years ago

// this distance method reference from https://stackoverflow.com/a/16794680/6138660

public static double distance(double lat1, double lat2, double lon1,
        double lon2) {
    final int R = 6371; // Radius of the earth

    double latDistance = Math.toRadians(lat2 - lat1);
    double lonDistance = Math.toRadians(lon2 - lon1);
    double a = Math.sin(latDistance / 2) * Math.sin(latDistance / 2)
            + Math.cos(Math.toRadians(lat1)) * Math.cos(Math.toRadians(lat2))
            * Math.sin(lonDistance / 2) * Math.sin(lonDistance / 2);
    double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
    double distance = R * c * 1000; // convert to meters

    distance = Math.pow(distance, 2);

    return Math.sqrt(distance);
}

private List<Unit> nearestUnits(List<Unit> lists, Unit x, int limit) {


    lists.sort(new Comparator<Unit>() {

        @Override
        public int compare(Unit o1, Unit o2) {

            double flagLat = x.getLat();
            double flagLon = x.getLon();

            double o1DistanceFromFlag = distance(flagLat, o1.getLat(), flagLon, o1.getLon());
            double o2DistanceFromFlag 
                                                    

                                                                                                                
                                                        
                                                    
                                                    

                                                        

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