NSSortDescriptor incorrectly sort date and strings, which are properties of custom class, but correctly sort integer

Question

I've created simple class Student with properties

@property (strong,nonatomic) NSString* firstname;
@property (strong,nonatomic) NSString* lastname;
@property (strong,nonatomic) NSDate* dateOfBirth;
@property (assign,nonatomic) NSInteger index;

After that, I created any objects of this class, gave it firstname, lastname, date and index, add all of them to self.InitialStudentsArray. And start sorting by dateOfBirth:

NSSortDescriptor* descriptorDate=[[NSSortDescriptor alloc]initWithKey:@"dateOfBirth" ascending:YES];
NSArray* descArray=[NSArray arrayWithObjects:descriptorDate, nil];
[self.InitialStudentsArray sortUsingDescriptors:descArray];

So, the result is strange. Array before sorting and after sorting have different items order, but not sorted at all by date.

before sort (
    "46 Alex  Dupel 25 10 1991",
    "236 Ivan  Evstegneev 20 09 1980",
    "179 Hugo  Igonin 03 02 1992",
    "189 Alexey  Boronenko 06 11 1978" ) 


after sort (
    "236 Ivan  Evstegneev 20 09 1980",
    "179 Hugo  Igonin 03 02 1992",
    "189 Alexey  Boronenko 06 11 1978",
    "46 Alex  Dupel 25 10 1991" )

The same thing with firstname and lastname (even if use selectors:

NSSortDescriptor* descriptorLastname=[[NSSortDescriptor alloc]initWithKey:@"lastname" ascending:YES selector:@selector(caseInsensitiveCompare:)];

It's only work for property "index",which is NSInteger.

What I've done else, I created array only with dates from student.dateOfBirth and sorted it with keyname self. And it works! Another experiment - I created array of dictionaries with key "dateOfBirth" and sorted it by key name @"dateOfBirth" and it also works!

I know about other methods live sortUsingComparator, but why this method doesn't work on date and strings in properties??

Upd Oh, guys, it's my mistake. I appreciate all of your answers, they pushed me to place, where to search mistake. And when I found it, I felt very ashamed. Absolutly stupid mistake. If you are interested in, I used this way to initialize student:

- (instancetype)init
{
    self = [super init];
    if (self) {
        self.firstname=[self getFirstname];
        self.lastname=[self getLastname];
        self.dateOfBirth=[self getDateOfBirth];
    }
    return self;
}
-(NSString*) getFirstname {//some code...arrayOfFirstames...name=arc4random()...}

I.e. I occasionally redefine getter for setting property. All three. So, when I was sorting array everytime new values was taken. Thank you.

They appear to be sorted by firstname with descending order. You should change your date format if you want it to sort correctly using string comparison. Instead of "DD MM YYYY" use "YYYY MM DD". — Ian MacDonald
If you use [descriptorDate compareObject:self.InitialStudentsArray[0] toObject:self.InitialStudensArray[1]], does it return the correct value? — Ian MacDonald
@Ian MacDonald, i've tried it and it may return correct value and may return incorrect. Like it doesn't depend on items. Like it depends on something else.. — NikLanf
You will have something else wrong. Can you show the accessors for 'InitialStudentsArray' for example? — Amin Negm-Awad
@Ian MacDonald, about your first note. It's just an accident, that they sorted by firstname with des order. In other times it doesn't. I want to sort date like NSDate and string like NSString. — NikLanf

Onik IV Onik IV · Accepted Answer · 2014-11-14T19:21:31

You might have wrong another thing, SortDescriptors work fine with strings, here an example:

NSArray *people = @[@{@"name": @"Ivan"},@{@"name": @"Hugo"},@{@"name": @"Alexey"},@{@"name": @"Alex"}];
NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];
NSArray *sorts = @[sort];
NSArray *orderedArray = [people sortedArrayUsingDescriptors:sorts];
NSLog(@"Show orderedArray: %@",[orderedArray description]);

Exit in console:

2014-11-14 20:19:45.377 pro[1366:60b] Show orderedArray: (
    {
    name = Alex;
},
    {
    name = Alexey;
},
    {
    name = Hugo;
},
    {
    name = Ivan;
}
)

I think it´s good idea to log your array before and after the sortedArrayUsingDescriptor methods.

Hi again. I´ve done the same again, with a Custom Class this is the header:

#import <Foundation/Foundation.h>

@interface CustomClass : NSObject

@property (nonatomic, strong) NSString *name;

@end

The implementation (.m) is blank, and again I´ve done:

CustomClass *ivan = [[CustomClass alloc] init];
ivan.name = @"Ivan";

CustomClass *hugo = [[CustomClass alloc] init];
hugo.name = @"Hugo";

CustomClass *alexey = [[CustomClass alloc] init];
alexey.name = @"Alexey";

CustomClass *alex = [[CustomClass alloc] init];
alex.name = @"Alex";


NSArray *people = @[ivan,hugo,alexey,alex];
NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];
NSArray *sorts = @[sort];
NSArray *orderedArray = [people sortedArrayUsingDescriptors:sorts];
 NSLog(@"Show orderedArray:");
for (CustomClass *people in orderedArray) {
    NSLog(@"%@\n",people.name);
}

And again, the exit console is:

 2014-11-14 22:38:13.297 pro[1406:147113] Show orderedArray:
 2014-11-14 22:38:13.298 pro[1406:147113] Alex
 2014-11-14 22:38:13.298 pro[1406:147113] Alexey
 2014-11-14 22:38:13.298 pro[1406:147113] Hugo
 2014-11-14 22:38:13.298 pro[1406:147113] Ivan

There isn´t any problem with sortDescriptors and property. Best

NSSortDescriptor incorrectly sort date and strings, which are properties of custom class, but correctly sort integer

1 Answers