How do I sort a swift array containing instances of NSManagedObject subclass by an attribute value (date)

Question

I'm trying to sort an array as laid out in the accepted answer to this question, but am running into the problem which Isuru mentions in the comments on that answer. Namely, the code which should sort the array by the entity's "date" attribute brings the compiler complaint "could not find member 'date'"

Here is the NSManagedObject subclass describing the entity:

import Foundation
import CoreData

@objc(Entry)
class Entry: NSManagedObject {

    @NSManaged var date: NSDate
    @NSManaged var reflections: AnyObject
    @NSManaged var contactComment: NSSet
    @NSManaged var person: NSSet

    override func awakeFromInsert() {
        let now:NSDate = NSDate()
        self.date = now;
    }
}

And here is the code which tries to sort the array:

lazy var entries:[Entry] = {
    var days:[Entry] = self.managedObjectContext!.requestEntity("Entry")as [Entry]
    days.sort({$0.date < $1.date})

    var today:Entry = days.last!
    println(today.date)
    return days
}()

Note that in the latter part of that code, I am able to access and log the "date" property for one of the entries, and the Compiler doesn't have a problem with it.

Is my syntax for sorting correct? Is there another issue with this code I'm not seeing?

Mike S · Accepted Answer · 2014-10-26T20:38:19.943

124

This is partly an issue with the Swift compiler not giving you a helpful error. The real issue is that NSDate can't be compared with < directly. Instead, you can use NSDate's compare method, like so:

days.sort({ $0.date.compare($1.date) == NSComparisonResult.OrderedAscending })

Alternatively, you could extend NSDate to implement the Comparable protocol so that it can be compared with < (and <=, >, >=, ==):

public func <(a: NSDate, b: NSDate) -> Bool {
    return a.compare(b) == NSComparisonResult.OrderedAscending
}

public func ==(a: NSDate, b: NSDate) -> Bool {
    return a.compare(b) == NSComparisonResult.OrderedSame
}

extension NSDate: Comparable { }

Note: You only need to implement < and == and shown above, then rest of the operators <=, >, etc. will be provided by the standard library.

With that in place, your original sort function should work just fine:

days.sort({ $0.date < $1.date })

edited Oct 26 '14 at 20:38

answered Oct 26 '14 at 20:31

Mike S

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This works perfectly for smaller amounts of data but when you have large amounts it takes a while to load. Is there a more efficient method? – nsij22 Jun 03 '15 at 14:28
@nsij22 since we're talking `NSManagedObject`s here, then those objects are probably coming from a core data store. In that case, the most efficient thing to do is probably to sort the data via the core data fetch request. Take a look at `NSFetchRequest.sortDescriptors`: https://developer.apple.com/library/mac/documentation/Cocoa/Reference/CoreDataFramework/Classes/NSFetchRequest_Class/index.html#//apple_ref/occ/instp/NSFetchRequest/sortDescriptors – Mike S Jun 04 '15 at 00:10

Fred Faust · Answer 2 · 2016-09-26T23:48:33.177

16

In Swift 3, dates are now directly comparable:

let aDate = Date()
let bDate = Date()

if aDate < bDate {

    print("ok")
}

Old swift: An alternative would be to sort on the timeIntervalSince1970 property of the date object, which is directly comparable.

days.sort({$0.date.timeIntervalSince1970 < $1.date.timeIntervalSince1970})

edited Sep 26 '16 at 23:48

answered Jan 14 '16 at 22:17

Fred Faust

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I only thought of it when I needed the same thing and saw the accepted answer's first sentence, which was quite later than when the accepted answer was posted. – Fred Faust Feb 12 '16 at 12:25

score 10 · Answer 3 · edited Jun 27 '16 at 10:09

10

In swift2.1 use this lines of code

array.sortInPlace({ $0.date.compare($1.date) == NSComparisonResult.OrderedAscending })

edited Jun 27 '16 at 10:09

Jigar Tarsariya

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answered Jan 21 '16 at 09:10

Phani Sai

1,215
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score 2 · Answer 4 · edited Feb 18 '19 at 08:17

2

Update__ Swift 4,

let sortedData = dataToSort.sorted(by: { (obj1, obj2) -> Bool in             
   return obj1.date < obj2. date
})

edited Feb 18 '19 at 08:17

Dmitry

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answered Feb 18 '19 at 07:58

Sagar Thukral

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score 0 · Answer 5 · answered Oct 13 '16 at 06:37

I having one dictionary whose keys are in the date format so i have to sort the dictionary by date . i copied all the keys in nsarray then sort that array by using the following code.

let keys : NSArray = stackedBarDataDict.allKeys // stackedBarDataDict is Data Dictionary
    let dataArray = NSMutableArray()
    for index in 0...(stackedBarDataDict.allKeys.count - 1)
    {
        let dateone = keys.objectAtIndex(index)
        let dateFormatter = NSDateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd"
        let date1 = dateFormatter.dateFromString(dateone as! String)
        dataArray.addObject(date1!)
    }
    let array : NSArray = (dataArray as NSArray)
        let sortedArray = array.sortedArrayUsingComparator {
        (obj1, obj2) -> NSComparisonResult in

        let p1 = obj1 as! NSDate
        let p2 = obj2 as! NSDate
        let result = p1.compare(p2)
        return result
    }
    print(sortedArray)

How do I sort a swift array containing instances of NSManagedObject subclass by an attribute value (date)

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