Swift: Sort Array by sort descriptors

Question

I am using coredata so I need sort descriptors for my entities

For example, a Coordinate-entity has this class func:

class func sortDescriptors() -> Array<NSSortDescriptor>
{
    return [NSSortDescriptor(key: "sequence", ascending: true)]
}

I am using this when doing fetch-requests to CoreData like this:

var request = NSFetchRequest(entityName: entityName)

request.sortDescriptors = T.sortDescriptors()

However, when I have an array of coordinates as a property on another coredata object, this is an NSSet (I.e. unsorted)

To solve this, I am returning the coordinates like this:

return NSArray(array: coordinates!).sortedArrayUsingDescriptors(Coordinate.sortDescriptors()) as? Array<Coordinate>

Which feels ugly, to use an NSArray just to get the sortedArrayUsingDescriptors-method. Is there a similar way to do this directly on a Swift-array, I.e. Array<Coordinate> by using sort descriptors?

Thank you!

Why don't you use `NSSet`'s `sortedArrayUsingDescriptors()` method? — rintaro, Nov 12 '14 at 09:40
I could do that aswell! But the question still stands; is sort sescriptors compatible with Swift-arrays? — ullstrm, Nov 12 '14 at 13:52
@rintaro `NSSet` instances are unordered by definition. I assume that you are referring to `NSArray`. — Bart Jacobs, Aug 24 '15 at 13:56

score 20 · Answer 1 · answered Jan 24 '16 at 09:04

20

Another approach to the nice extensions of Damien could be a multi-cast.

myArray = (myArray as NSArray).sortedArrayUsingDescriptors(tableView.sortDescriptors) as! Array

Original source: NSHipster

answered Jan 24 '16 at 09:04

Tobonaut

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score 10 · Answer 2 · answered Jan 05 '16 at 08:25

There is no built-in method for this, but you can add them using protocol extension:

extension MutableCollectionType where Index : RandomAccessIndexType, Generator.Element : AnyObject {
    /// Sort `self` in-place using criteria stored in a NSSortDescriptors array
    public mutating func sortInPlace(sortDescriptors theSortDescs: [NSSortDescriptor]) {
        sortInPlace {
            for sortDesc in theSortDescs {
                switch sortDesc.compareObject($0, toObject: $1) {
                case .OrderedAscending: return true
                case .OrderedDescending: return false
                case .OrderedSame: continue
                }
            }
            return false
        }
    }
}

extension SequenceType where Generator.Element : AnyObject {
    /// Return an `Array` containing the sorted elements of `source`
    /// using criteria stored in a NSSortDescriptors array.
    @warn_unused_result
    public func sort(sortDescriptors theSortDescs: [NSSortDescriptor]) -> [Self.Generator.Element] {
        return sort {
            for sortDesc in theSortDescs {
                switch sortDesc.compareObject($0, toObject: $1) {
                case .OrderedAscending: return true
                case .OrderedDescending: return false
                case .OrderedSame: continue
                }
            }
            return false
        }
    }
}

But note that this will work only when the array elements are classes, not structures, as NSSortDescriptor compareObject method requires arguments conforming to AnyObject

Big kudos to you! This was a mind-freaking issue for me. Thanks for helping me out. — Tobonaut, Jan 24 '16 at 08:59

score 7 · Answer 3 · answered Feb 18 '17 at 09:21

Swift 3 Version of @Darniel's answer

extension MutableCollection where Self : RandomAccessCollection {
    /// Sort `self` in-place using criteria stored in a NSSortDescriptors array
    public mutating func sort(sortDescriptors theSortDescs: [NSSortDescriptor]) {
        sort { by:
            for sortDesc in theSortDescs {
                switch sortDesc.compare($0, to: $1) {
                case .orderedAscending: return true
                case .orderedDescending: return false
                case .orderedSame: continue
                }
            }
            return false
        }

    }
}

extension Sequence where Iterator.Element : AnyObject {
    /// Return an `Array` containing the sorted elements of `source`
    /// using criteria stored in a NSSortDescriptors array.

    public func sorted(sortDescriptors theSortDescs: [NSSortDescriptor]) -> [Self.Iterator.Element] {
        return sorted {
            for sortDesc in theSortDescs {
                switch sortDesc.compare($0, to: $1) {
                case .orderedAscending: return true
                case .orderedDescending: return false
                case .orderedSame: continue
                }
            }
            return false
        }
    }
}

Swift: Sort Array by sort descriptors

3 Answers3

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