You can specify a sort when you retrieve data with an NSFetchRequest by setting the sortDescriptors property to an array of NSSortDescriptors. But if you already have it in an NSSet and don’t want to make another fetch request, you can use: [[theSet allObjects] sortedArrayUsingDescriptors:sortDescriptors]; It’ll create an interim NSArray when you call allObjects and … Read more
There is no Objective-C literal syntax for NSSet. It doesn’t really make sense to use index subscripting to access NSSet elements, although key-based subscripting might. Either by wrapping or subclassing, you could add your own. (Correction): Originally I had thought NSOrderedSet wasn’t supported either, but it turns out that using index subscripting is supported, but … Read more
Despite you’re casting NSMutableSet to NSArray, that simple casting won’t make NSSet class respond to NSArray‘s messages. You have to fill an actual NSArray with the elements of the NSSet like this: NSArray *array = [theNsSet allObjects];
I went through the interface of NSSet and you’re right, ordered sets appear to satisfy the Liskov substitution principle and could therefor inherit from NSSet. There is one little method that breaks this: mutableCopy. The return value of mutableCopy must be an NSMutableSet, but NSMutableOrderedSet should inherit from NSOrderedSet. You can’t have both. Let me … Read more
NSPredicate *predicate = [NSPredicate predicateWithFormat:@”type == %@”, @”standard”]; NSArray *filteredArray = [myArray filteredArrayUsingPredicate:predicate]; id firstFoundObject = nil; firstFoundObject = filteredArray.count > 0 ? filteredArray.firstObject : nil; NB: The notion of the first found object in an NSSet makes no sense since the order of the objects in a set is undefined.
As of Swift 1.2 (Xcode 6.3 beta), Swift has a native set type. From the release notes: A new Set data structure is included which provides a generic collection of unique elements, with full value semantics. It bridges with NSSet, providing functionality analogous to Array and Dictionary. Here are some simple usage examples: // Create … Read more
This will return an array containing the value of licensePlate from each item in the myCars array: NSArray *licensePlates = [myCars valueForKeyPath:@”licensePlate”] If you want only unique items (for example), you can do something like this: NSArray *licensePlates = [myCars valueForKeyPath:@”@distinctUnionOfObjects.licensePlate”]; For more possibilities, see the Collection Operators documentation in the Key-Value Coding Programming Guide.
try using [[mySet allObjects] sortedArrayUsingDescriptors:descriptors]; Edit: For iOS ≥ 4.0 and Mac OS X ≥ 10.6 you can directly use [mySet sortedArrayUsingDescriptors:descriptors];
There are several use cases for a set. You could enumerate through (e.g. with enumerateObjectsUsingBlock or NSFastEnumeration), call containsObject to test for membership, use anyObject to get a member (not random), or convert it to an array (in no particular order) with allObjects. A set is appropriate when you don’t want duplicates, don’t care about … Read more
Since -allObjects returns an array, you can create a mutable version with: NSMutableArray *array = [NSMutableArray arrayWithArray:[set allObjects]]; Or, alternatively, if you want to handle the object ownership: NSMutableArray *array = [[set allObjects] mutableCopy];