Sorting two NSMutableArrays by 'nearest distance' first - iphone

Question

I have two arrays, both full of NSString objects like this:
NSMutableArray *titles = [[NSMutableArray alloc] initWithObjects:#"Title1", #"Title2", #"Title3", #"Title4", #"Title5", nil];
NSMutableArray *distances = [[NSMutableArray alloc] initWithObjects:#"139.45", #"23.78", #"347.82", #"10.29", #"8.29", nil];
How can I sort both arrays by the nearest distance first?
So the results would be like this:
titles = #"Title5", #"Title4", #"Title2", #"Title1", #"Title3"
distances = #"8.29", #"10.29", #"23.78", #"139.45", #"347.82"
I understand that NSSortDescriptor can be used in these circumstances but after looking through the documentation, I am still unsure about how.

Answer 1

I would sort the distances this way...
NSNumberFormatter *f = [[NSNumberFormatter alloc] init];
[f setNumberStyle:NSNumberFormatterDecimalStyle];
NSArray *sortedDistances = [listItem sortedArrayUsingComparator: ^(id a, id b) {
NSNumber *aNum = [f numberFromString:a];
NSNumber *bNum = [f numberFromString:b];
return [aNum compare:bNum];
}];
I can't think of a particularly quick way to get the associated titles sorted, but this should work ...
NSMutableArray *sortedTitles = [NSMutableArray array];
NSDictionary *distanceTitle = [NSDictionary dictionaryWithObjects:titles forKeys:distances];
for (NSString *distance in sortedDistances) {
NSString *associatedTitle = [distanceTitle valueForKey:distance];
[sortedTitles addObject:associatedTitle];
}

Answer 2

You can use an NSComparator block and use NSArray's sortedArrayUsingComparator method. On that block, you will receive two objects to compare, and base on the comparison result, you can use NSMutableArray exchangeObjectAtIndex:withObjectAtIndex: method to change the values of titles.

Answer 3

Here is a sample how I sort an array of dictionaries by distance value:
-(void)reorderByDistance {
NSSortDescriptor *sortByName = [NSSortDescriptor sortDescriptorWithKey:#"distance" ascending:YES];
NSArray *sortDescriptors = [NSArray arrayWithObject:sortByName];
self.contentArray = [self.contentArray sortedArrayUsingDescriptors:sortDescriptors];
}
And my dictionary looks like this:
NSDictionary *dict1 = [[NSDictionary alloc] initWithObjectsAndKeys:#"1", #"id", #"Business #1", #"name", #"This business does some pretty remarkable things", #"description", #"Alley Bar", #"category", #"1.2", #"distance", nil];

Answer 4

One approach would be to create a dictionary mapping titles to distances, sort the distances, and then iterate through the distances to recreate the titles:
NSMutableArray *titles = [[NSMutableArray alloc] initWithObjects:#"Title1", #"Title2", #"Title3", #"Title4", #"Title5", nil];
NSMutableArray *distances = [[NSMutableArray alloc] initWithObjects:#"139.45", #"23.78", #"347.82", #"10.29", #"8.29", nil];
//Create a map of current titles to distances
NSDictionary *titleDistanceMap = [NSDictionary dictionaryWithObjects:titles forKeys:distances];
//Need to sort the strings as numerical values
[distances sortUsingComparator:^(NSString *obj1, NSString *obj2) {
return [obj1 compare:obj2 options:NSNumericSearch];
}];
//Now re-populate the titles array
[titles removeAllObjects];
for (NSString *distance in distances){
[titles addObject:[titleDistanceMap objectForKey:distance]];
}