Android – Sort list of lon\lat points, start with nearest

androiddistancegpspointsorting

I have location from GPS (lon_base, lat_base).
I have a list of locations (lon1, lat1|lon2, lat2|lon3, lat3…)
This list is very long and is around the world.

My questions are:
1. How do I get from that list only the lon\lat that are 1 mile from my lon_base\lat_base?
2. How do I sort them from closest to farthest?

Thanks in advance!

Best Answer

public static List<Location> sortLocations(List<Location> locations, final double myLatitude,final double myLongitude) {
    Comparator comp = new Comparator<Location>() {
        @Override
        public int compare(Location o, Location o2) {
            float[] result1 = new float[3];
            android.location.Location.distanceBetween(myLatitude, myLongitude, o.Lat, o.Long, result1);
            Float distance1 = result1[0];

            float[] result2 = new float[3];
            android.location.Location.distanceBetween(myLatitude, myLongitude, o2.Lat, o2.Long, result2);
            Float distance2 = result2[0];

            return distance1.compareTo(distance2);
        }
    };


    Collections.sort(locations, comp);
    return locations;
}

Where the List of Locations is a list containing your own Location class, not the android.location.Location.

Compare method

Either you implement a compare-method for your object:

- (NSComparisonResult)compare:(Person *)otherObject {
    return [self.birthDate compare:otherObject.birthDate];
}

NSArray *sortedArray = [drinkDetails sortedArrayUsingSelector:@selector(compare:)];

NSSortDescriptor (better)

or usually even better:

NSSortDescriptor *sortDescriptor;
sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"birthDate"
                                           ascending:YES];
NSArray *sortedArray = [drinkDetails sortedArrayUsingDescriptors:@[sortDescriptor]];

You can easily sort by multiple keys by adding more than one to the array. Using custom comparator-methods is possible as well. Have a look at the documentation.

Blocks (shiny!)

There's also the possibility of sorting with a block since Mac OS X 10.6 and iOS 4:

NSArray *sortedArray;
sortedArray = [drinkDetails sortedArrayUsingComparator:^NSComparisonResult(Person *a, Person *b) {
    return [a.birthDate compare:b.birthDate];
}];

Performance

The -compare: and block-based methods will be quite a bit faster, in general, than using NSSortDescriptor as the latter relies on KVC. The primary advantage of the NSSortDescriptor method is that it provides a way to define your sort order using data, rather than code, which makes it easy to e.g. set things up so users can sort an NSTableView by clicking on the header row.

Best Answer

Related Solutions

Python – How to sort a list of dictionaries by a value of the dictionary

Ios – How to sort an NSMutableArray with custom objects in it

Compare method

NSSortDescriptor (better)

Blocks (shiny!)

Performance

Related Topic