How can I sort a NSArray by NSSortDiscriptor?

Question

I am new in iPhone development. I need your help in sorting NSArray.

in this Code I am assigning values to the MyData. this is a NSArray variable.

NSMutableArray *MyArray=[NSMutableArray array];

[MyArray addObject:[NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:314564454],@"Population", @"Mumbai",@"Name", [NSNumber numberWithInt:415452],@"Area",nil]];

[MyArray addObject:[NSDictionary dictionaryWithObjectsAndKeys[NSNumber numberWithInt:454154412],@"Population", @"Chennai",@"Name", [NSNumber numberWithInt:324544],@"Area",nil]];

[MyArray addObject:[NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:874544541],@"Population", @"Kolkatta",@"Name", [NSNumber numberWithInt:554445],@"Area",nil]];

[MyArray addObject:[NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:412541245],@"Population", @"Delhi",@"Name", [NSNumber numberWithInt:345475],@"Area",nil]];

self.MyData = [NSArray arrayWithArray:MyArray];

Now I need top 3 Cities with the Highest Population Information.

So I had Write Following Code.,

NSSortDescriptor *sorter = [[[NSSortDescriptor alloc] initWithKey:@"Population" ascending:NO] autorelease]; 
NSArray *sorted = [self.MyData sortedArrayUsingDescriptors: 
    [NSArray arrayWithObject:sorter]];   

NSRange range = NSMakeRange(0,3); 
return [sorted subarrayWithRange:range];

But it is not working. The same code works if I replace the following

NSSortDescriptor *sorter = [[[NSSortDescriptor alloc] initWithKey:@"Population" ascending:NO] autorelease]; 

with

NSSortDescriptor *sorter = [[[NSSortDescriptor alloc] initWithKey:@"Name" ascending:NO] autorelease]; 

This Works.. Because Name is String. Please help me out How can I sort this array with numeric value.

Thank you in advance.

Answer 1

A quick run of your code gives to following output which seems right for me:

2010-07-29 16:32:59.774 test[93035:207] (
    {
    Area = 554445;
    Name = Kolkatta;
    Population = 874544541;
},
    {
    Area = 324544;
    Name = Chennai;
    Population = 454154412;
},
    {
    Area = 345475;
    Name = Delhi;
    Population = 412541245;
}
)

I just replaced your return with: NSLog(@"%@", [sorted subarrayWithRange:range]);

Cheers...