Question

I have an array of points on a map.
I populate the array correctly and I make annotations for them on the map. everything is working fine.
I have another tableview with the same array, and in the “subtitle” of the cells, I calculate the distance to user and present. everything working fine.

Now,I want to sort the list in the table view, in other words I want to sort the same array by distance, lowest to highest.

The thing is that the distance is not part of the array. so how can I cross match the distance with the array, so that when I sort the distance, it takes its belonging object in the array with it and sorts the array as well?

I am fairly new to ios but I have managed to release 3 apps now, and this one is the fourth, far more complex and I think I have covered pretty good ground with making the app so far. From the mapview, to the tableview with a search controller and everything. I am only missing the sorting.

I imagine I need to add some tag or property to each object in the array and assign it to each distance in the distance array.
Any suggestions would be appreciated 🙂
Thanks in advance.

Answer 1

// Assuming you have your points on the map in an NSArray called
// pointsOnMapArray and your distances in distanceArray, create a
// new mutable array to hold both.  Note, the "distances" in this
// case are stored as NSStrings.  We'll want to convert them to
// doubles before sorting them.
NSMutableArray *newArray = [[NSMutableArray alloc] init];

// Iterate over all of the points, and add a new element to the mutable
// array which is a new array containing a point and its distance.  The
// distance is converted from an NSString to an NSNumber containing a
// doubleValue.
int i;   
for (i = 0; i < pointsOnMapArray.count; i++) {
    NSArray *newItem = [NSArray arrayWithObjects: [pointsOnMapArray objectAtIndex: i], [NSNumber numberWithDouble:[[distanceArray objectAtIndex: i] doubleValue]], nil];
    [newArray addObject: newItem];
}

// Now, sort the new array based upon the distance in the second element
// of each array (ie, the distance).
[newArray sortUsingComparator: ^(id obj1, id obj2) {
    NSNumber *dist1 = [obj1 objectAtIndex:1];
    NSNumber *dist2 = [obj2 objectAtIndex:1];

    return [dist1 compare:dist2];
}];