sorting NSmutable array contains object according to double value

Question

I want to order NSMutableArray contain objects according to two of object property one of them has double type second has NSString ?

I tried to use this method but I got exception :

NSString * LASTNAME = @"lastName";
NSString * GRADE = @"grade";

NSSortDescriptor *lastDescriptor =
    [[NSSortDescriptor alloc]
        initWithKey:LASTNAME
          ascending:YES
           selector:@selector(localizedCaseInsensitiveCompare:)];

NSSortDescriptor *firstDescriptor =
    [[NSSortDescriptor alloc]
        initWithKey:GRADE
          ascending:YES
           selector:@selector(localizedCaseInsensitiveCompare:)]];

NSArray * descriptors =
   [NSArray arrayWithObjects:lastDescriptor, firstDescriptor, nil];
NSArray * sortedArray =
   [students sortedArrayUsingDescriptors:descriptors];

@interface Student : NSObject
{
    NSString * firstName;
    NSString * lastName;
    double grade;
}

Answer 1

NSNumber doesn't respond to localizedCaseInsensitiveCompare:. You want just plain compare: for the number.

Answer 2

Numbers don't have a case, try using compare: for GRADE

After Edit: You didn't say what error you got. Did the code you posted even compile? You have a typo in your firstDescriptor -- one too many "]" at the end of the method. You probably fixed that when you took out the compare: (which shouldn't have fixed anything).

Answer 3

Remove localizedCaseInsensitiveCompare

NSSortDescriptor *firstDescriptor =
    [[NSSortDescriptor alloc]
        initWithKey:GRADE
          ascending:YES]];