ios - Sort NSFetchRequest by calculation result -


so have dataset of points latitude , longitude values , want retrieve them , sort them distance user's current location. currently, have following:

mainmoc.performblockandwait {             // fetching data coredata             let fetchrequest = nsfetchrequest()             fetchrequest.predicate = nspredicate(format: "pointlatitude between {%f,%f} , pointlongitude between {%f,%f}", (latitude-0.03), (latitude+0.03), (longitude-0.03), (longitude+0.03))             let entity = nsentitydescription.entityforname("pointprimary", inmanagedobjectcontext: self.mainmoc)             fetchrequest.entity = entity              let sortdescriptor = nssortdescriptor(key: "pointtitle", ascending: false)             fetchrequest.sortdescriptors = [sortdescriptor]              {                 points = try self.mainmoc.executefetchrequest(fetchrequest) as! [pointprimary]              } catch {                 let jsonerror = error nserror                 nslog("\(jsonerror), \(jsonerror.localizeddescription)")                 abort()             }         }

so i'm sorting based on title. how proceed if wanted calculate distance cllocationcoordinate2d , sort fetchrequest results based on that?

thanks bunch!

this should work. you'll use nssortdescriptor custom comparator.

the trick use "self" key nssortdescriptor, pass fetched objects comparator. 

var userlocation : cllocation // somewhere var distancecompare : nscomparator = {     (obj1: anyobject!, obj2: anyobject!) -> nscomparisonresult in     let lng1 = obj1.valueforkey("pointlongitude") as! cllocationdegrees     let lat1 = obj1.valueforkey("pointlatitude") as! cllocationdegrees     let p1location : cllocation = cllocation(latitude: lat1, longitude: lng1)     let p1distancetouserlocation = userlocation.distancefromlocation(p1location)      let lng2 = obj2.valueforkey("pointlongitude") as! cllocationdegrees     let lat2 = obj2.valueforkey("pointlatitude") as! cllocationdegrees     let p2location : cllocation = cllocation(latitude: lat1, longitude: lng1)     let p2distancetouserlocation = userlocation.distancefromlocation(p2location)      if (p1distancetouserlocation > p2distancetouserlocation) {         return .ordereddescending     } else if (p1distancetouserlocation < p2distancetouserlocation) {         return .orderedascending     } else {         return .orderedsame     } }  var distancesortdescriptor = nssortdescriptor(key: "self", ascending: true, comparator: distancecompare) fetchrequest.sortdescriptors = [distancesortdescriptor]

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