How to sort an Array based off on another array

Question

I'm developing an Android app. I need to sort an array based off of the sorting of another. I'm sorting one (distance) based off of lowest to highest, and need for my longitude values to be sorted according to the distance. So say if distance 5 had longitude 41.2265 and distance 6 had longitude 41.2187, I would need to sort the distances from lowest to highest, {5,6}, and then sort the longitudes based off of their first pair. I have read that you could do this with a 2D array, but I would prefer not to do this. I think this also could be done with mapping, but I'm not sure how. My code is below:

Part of NearestStations.java

            ArrayList<String> distancetos = new ArrayList<String>();
            ArrayList<String> longitudeArray = new ArrayList<String>();

            while(iterator.hasNext()){
            for (int i=0; i<144;i++){

            double distance = 0;  

            double lat_end = 0;
            double lon_end = 0;


            try {
                lat_end = Double.parseDouble(iterator.next());
                lon_end = Double.parseDouble(iterator1.next());
                longitudeArray.add(Double.toString(lon_end));
                Log.i("Lon_end", String.valueOf(lon_end));

            } catch (NumberFormatException e) {
                Log.v("Main", "Convert to Double Failed : ");
            }

            Location locationA = new Location("point A");  
            locationA.setLatitude(latitude);  
            locationA.setLongitude(longitude);  

            Location locationB = new Location("point B");  
            locationB.setLatitude(lat_end);  
            locationB.setLongitude(lon_end);  

            distance = locationA.distanceTo(locationB) * 0.000621371192237334;
            Log.i("distancebefore", String.valueOf(distance));

            String dista = Double.toString(distance);


            distancetos.add(dista);
            }
            }


                Collections.sort(distancetos);

                distancea = distancetos.get(0);
                distance1 = distancetos.get(1);

                String Longa = longitudeArray.get(0);
                String Long1 = longitudeArray.get(1);


                Log.i("distanceafter", String.valueOf(distancea));
                Log.i("distance1after", String.valueOf(distance1));


            String[] Stations = getResources().getStringArray(R.array.Stations);
            String[] Longitude = getResources().getStringArray(R.array.Longitude);
            String[] Latitude = getResources().getStringArray(R.array.Latitude);



            Map<String, String> myMap = new HashMap<String, String>();{
            for (int i = 0; i <144; i++) {
                myMap.put(Latitude[i], Stations[i]);
            }
            }

            Map<String, String> myMap1 = new HashMap<String, String>();{
            for (int h = 0; h <144; h++) {
                myMap1.put(Longitude[h], Stations[h]);

            }
            }

            String value = myMap1.get(Longa);
   }
}

Thank you for your help.

Answer 1

I believe this is what you're looking for.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.ListIterator;

public class GenericCachedSorter {
    public static void main(String[] args) {
        List<Double> distances = new ArrayList<>(Arrays.asList(1d, 2d, 3d));

        sort(distances, new ToComparable<Double, Double>() {
            @Override
            public Double toComparable(Double distance) {
                // return the longitude associated with this distance
                return getLongitude(distance);
            }
        });

        for (Double distance : distances)
            System.out.println(distances);
    }

    public interface ToComparable<T, C extends Comparable<? super C>> {
         C toComparable(T t);
    }

    public static <T, C extends Comparable<? super C>> void sort(List<T> list, ToComparable<T, C> function) {
       class Pair implements Comparable<Pair> {
          final T original;
          final C comparable;

          Pair(T original, C comparable) {
             this.original = original;
             this.comparable = comparable;
          }

          @Override
          public int compareTo(Pair other) {
                return
                  comparable == null && other.comparable == null ? 0 :
                  comparable == null ? -1 :
                  other.comparable == null ? 1 :
                  comparable.compareTo(other.comparable);
          }
       }

       List<Pair> pairs = new ArrayList<>(list.size());
       for (T original : list)
          pairs.add(new Pair(original, function.toComparable(original)));

       Collections.sort(pairs);

       ListIterator<T> iter = list.listIterator();
       for (Pair pair : pairs) {
          iter.next();
          iter.set(pair.original);
       }
    }
}

Answer 2

How about making a class for them?

public class Coord{
    private int id;
    private double lat;
    private double long;

    public double getDistanceFrom(Coord coord);

}

That should help you because it decouples locations from administrative tasks - if you were writing C your approach would be a good one. But you're writing Java.

Moreover: The for loop will silently fail because you deplete the iterator without checking for a hasNext() . That's only done at the outer loop. So

int i=0;
while(iterator.hasNext() && iterator1.hasNext()){ //also check iterator1
     if(i>=144) break; //that's what your for loop essentially did
        double distance = 0;  
        double lat_end = 0;
        double lon_end = 0;

        try {
            lat_end = Double.parseDouble(iterator.next());
            lon_end = Double.parseDouble(iterator1.next());
            CoordArray.add(new Coord(lat_end, lat_long));
            Log.i("Lon_end", String.valueOf(lon_end));

        } catch (NumberFormatException e) { ... }
//more stuff here
i++;
}/*while loop*/