title: Deleting duplicates in an array of annotations
body: <p>I have a MKMapKit I'm populating with annotations using data I'm fetching from an API. Each annotation has a title, description, URL, and coordinates. I have a button I added to a navigation bar to fetch more results and populate more annotations. The problem is when the API runs of out new results in populates the map with duplicates of annotations that were already fetched. I'm trying to delete duplicate annotations from an array using an if statement but it's not working. Any suggestions? Thanks in advance. </p>
  
  <pre><code>-(void)layAnnotations
  {
  
  if (self.annotations) {
      [self.mapView removeAnnotations:self.annotations];
  }
  
  self.annotations = [NSMutableArray array];
  
  for (Object *aObject in self.objectArray) {
      CLLocationCoordinate2D coordinate;
      coordinate.latitude = [aObject.latitude floatValue];
      coordinate.longitude = [aObject.longitude floatValue];
  
      Annotations *annotation = [[Annotations alloc] init];
  
  
  
      annotation.title = aObject.objectTitle;
      annotation.subtitle = aObject.description;
      annotation.url = aObject.url;
      annotation.coordinate = coordinate;
  
      //attempting to filter duplicates here
      if (![self.annotations containsObject:annotation]) {
          [self.annotations addObject:annotation];
      }        
  
      annotation = nil;
  
  }
  
  [self mutateCoordinatesOfClashingAnnotations:self.annotations];
  
  [self.mapView addAnnotations:self.annotations];
  
  }
  </code></pre>