NSSortDescriptor evaluating ascending numbers (Swift)

Question

App has contentid coming in as a number string from a json file:

let contentid: AnyObject! = jsonFeed["contentid"]

let stream:Dictionary = [
   "contentId": contentid as! String,
]

It is later saved to [NSManagedObject] with:

var articles = [NSManagedObject]()

let entity =  NSEntityDescription.entityForName("Article", inManagedObjectContext: managedContext)
let article = NSManagedObject(entity: entity!, insertIntoManagedObjectContext: managedContext)

article.setValue(stream["contentId"], forKey: "contentid")

articles.append(article)

Finally, I use NSSortDescriptor to have Core Data return entries in numerical ascending order:

let sort = NSSortDescriptor(key: "contentid", ascending: true)
fetchRequest.sortDescriptors = [sort]

But entries 6 - 10 are returned as: 10, 6, 7, 8, 9. What would be the correct method of having these numbers evaluated correctly using NSSortDescriptor?

UPDATE:

For the Swift version, please see Volker's answer below. I ended up using:

let sort = NSSortDescriptor(key: "contentid", ascending: true, selector: "localizedStandardCompare:")

and it evaluated the numbered strings as true integers.

UPDATE: Swift 2:

Selector syntax has changed and no longer accepts objc pointers. Thank you user1828845.

let sort = NSSortDescriptor(key: "contentid", ascending: true, selector: #selector(NSString.localizedStandardCompare(_:)))

Oliveolivegreen

is contentid a number or a string internally? – Moonfaced

@Moonfaced It is a string internally. – Oliveolivegreen

Descriptor is treating these as numbers. Thats why it is showing 10 before 6. Possible solution is treat these numbers as NSString. – Elsa

Please post more code for clarification. – Elsa

@Volker, so I should convert the string to a Int32 and store it as such? Abdul Yasin was implying that it needs to be a String, no? – Oliveolivegreen

while an Int32 will help you may also see the duplicate question that has another answer, that is more flexibel and maybe easier. should be easy to get that into Swift quickly. – Moonfaced

There exists init(key:ascending:selector:) and there you can use selector: "localizedStandardCompare:"as described here for example nshipster.com/nssortdescriptor – Moonfaced

@Volker, it worked perfectly. Thank you for the link as finding Swift code references are limited thus far. I went with: let sort = NSSortDescriptor(key: "contentid", ascending: true, selector: "localizedStandardCompare:") – Oliveolivegreen

Answer 1

The values you want to sort are actually strings and not numbers, thus the strange sort order. For Swift there exist an initializer init(key:ascending:selector:) of NSSortDescriptorand thus you can use selector: "localizedStandardCompare:" as described for example at nshipster.com/nssortdescriptor

The localizedStandardCompare: gives you a Finder like sorting of string values in a way that numbers are sorted naturally as you would sort numbers. So 1,...,9,10,...,99, 100 etc.

Moonfaced

Answer 2

In my case I tried it with

let descriptor: NSSortDescriptor = NSSortDescriptor(key: "formId", ascending: true, selector: #selector(NSString.localizedStandardCompare(_:))) Its working for me.

Creative

Answer 3

        let descriptor: NSSortDescriptor = NSSortDescriptor(key: "message_time", ascending: true)
        let sortedResults = arrayForMessages.sortedArray(using: [descriptor])
        print(sortedResults)

Lyle