I need to get the penultimate result from a for loop - ios

Question

I have an array of waypoints stored which have latitude and longitude values. I have created a for loop to loop through the array and compare my current CLLocation positions latitude and longitude to find which of the waypoints i am closest to. I also need to get the second closest waypoint and store this ac s a CLLocation object as well but cannot get it working.
The logic would be something like this
am I closest
yes
move closest location to second closest
set as second closest
loop again to get the closest point
My code:
-(void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations{
//set latestlocation as the last object from the locations array
CLLocation *currentLocation = [locations lastObject];
//declare a closestpoint object
CLLocation *closestWayPointToCurrentLocation;
//declare a second closest point object
CLLocation *secondClosestWayPointToCurrentLocation;
//set the distance to a high number
float distance = 10000000;
float secondClosestWaypointDistance = 10000000;
//load in plist
NSString *plistName = [self.mapsInfo objectForKey:#"plistName"];
NSString *path = [[NSBundle mainBundle] pathForResource:#"Chester" ofType:#"plist"];
NSString *path = [[NSBundle mainBundle] pathForResource:plistName ofType:#"plist"];
//store in array called waypoints
NSArray *waypoints= [NSArray arrayWithContentsOfFile:path];
//declare a variable for locationNum (the waypoints)
int locationNum = 0;
for (NSDictionary *point in waypoints) {
CLLocation *waypointLocation = [[CLLocation alloc]initWithLatitude:[(NSNumber *)[point objectForKey:#"Lat"]floatValue] longitude:[(NSNumber *)[point objectForKey:#"Long"]floatValue]];
float waypointDistanceFromCurrentLocation = [currentLocation distanceFromLocation:waypointLocation];
//secondClosestWayPointToCurrentLocation = waypointLocation;
if(waypointDistanceFromCurrentLocation < distance) {
//todo: move the current closestWayPointToCurrentLocation into second postion
//update the second closest waypoint distance variable also with distance
distance = waypointDistanceFromCurrentLocation;
closestWayPointToCurrentLocation = waypointLocation;
if(closestWayPointToCurrentLocation == waypointLocation) {
}
}
else
{
//check against the second position
//if closer than second position, replace it with new waypoint with code similar to above
}

Answer 1

If you are sure the point you is always the penultimate then you can retrive it like this
int totalNumberOfWaypoints = [waypoints count];
//Get penultimate waypoints
NSDictionary *penultimateWaypoint = [waypoints objectAtIndex:(totalNumberOfWaypoints - 2)];

Answer 2

Why dont you just make a sorted array of points, sorted by distance in ascending order?
NSMutableArray *waypoints= [NSArray arrayWithContentsOfFile:path];
for (NSDictionary *point in waypoints) {
[waypoints sortUsingComparator: (NSComparisonResult) ^ (id obj1, id obj2) {
CLLocation *waypointLocation1 = [[CLLocation alloc]initWithLatitude:[(NSNumber *)[obj1 objectForKey:#"Lat"]floatValue] longitude:[(NSNumber *)[obj1 objectForKey:#"Long"]floatValue]];
CLLocation *waypointLocation2 = [[CLLocation alloc]initWithLatitude:[(NSNumber *)[obj2 objectForKey:#"Lat"]floatValue] longitude:[(NSNumber *)[obj2 objectForKey:#"Long"]floatValue]];
float distance1 = [currentLocation distanceFromLocation:waypointLocation1];
float distance2 = [currentLocation distanceFromLocation:waypointLocation2];
if (distance1 < distance2) {
return NSOrderedAscending;
}
else if (distance1 > distance2) {
return NSOrderedDescending
}
else
return NSOrderedSame;
}];
This way you can always have the closest point at [waypoints objectAtIndex:0] and second closest point at [waypoints objectAtIndex:1] and so on.
less work, better result IMHO