Find nearest annotations from user location ios?

Question

I have an array of annotations.I am calculating the distance between each annotation from user location.What I want to know is, how can I find lets say 3 nearest annotations from these distances?

Here is how I am calculating distance from user location to annotations.

  CLLocation *userLocation = self.mapView.userLocation.location;

  for (Annotation *obj in annotations) {

       CLLocation *loc = [[CLLocation alloc] initWithLatitude:obj.coordinate.latitude longitude:obj.coordinate.longitude];
      //  CLLocation *userLocation = [[CLLocation alloc] initWithLatitude:self.mapView.userLocation.coordinate.latitude longitude:self.mapView.userLocation.coordinate.longitude];
        CLLocationDistance dist = [loc distanceFromLocation:userLocation];
        int distance = dist;
        NSLog(@"Distance from Annotations - %i", distance);


    }

Answer 1

The userLocation is static, so don't recreate it each time in your loop. You can also get the location directly with:

CLLocation *userLocation = self.mapView.userLocation.location;

Then, you could do something like, store your distance numbers and annotations into a dictionary, with the distances as keys and the annotations as the values. Once the dictionary is built, sort the allKeys array and then you can get the annotations associated with the first 3 keys.

---

Assuming that you always have at least one annotation when you run this:

CLLocation *userLocation = self.mapView.userLocation.location;
NSMutableDictionary *distances = [NSMutableDictionary dictionary];

for (Annotation *obj in annotations) {
    CLLocation *loc = [[CLLocation alloc] initWithLatitude:obj.coordinate.latitude longitude:obj.coordinate.longitude];
    CLLocationDistance distance = [loc distanceFromLocation:userLocation];

    NSLog(@"Distance from Annotations - %f", distance);

    [distances setObject:obj forKey:@( distance )];
}

NSArray *sortedKeys = [[distances allKeys] sortedArrayUsingSelector:@selector(compare:)];
NSArray *closestKeys = [sortedKeys subarrayWithRange:NSMakeRange(0, MIN(3, sortedKeys.count))];

NSArray *closestAnnotations = [distances objectsForKeys:closestKeys notFoundMarker:[NSNull null]];

Answer 2

NSArray *numbers = [NSArray arrayWithObjects:
                    [NSNumber numberWithInt:0],
                    [NSNumber numberWithInt:3],
                    [NSNumber numberWithInt:2],
                    [NSNumber numberWithInt:8],
                    nil];

NSSortDescriptor* sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:nil ascending:YES selector:@selector(localizedCompare:)];
NSArray *sortedNumbers = [numbers sortedArrayUsingDescriptors:[NSArray arrayWithObject:sortDescriptor]];

you store all distance in an array and sort it and then pick up top there number

[sortedNumbers objectAtIndex:0];
[sortedNumbers objectAtIndex:1];
[sortedNumbers objectAtIndex:2];