How can i shuffle RLMResults in swift?

Question

Any idea how can i shuffle randomly for RLMResults? I couldn't find anyway to do it via RLMSortDescriptor.

I tried writing my own swap algorithm, but it's giving me error (cannot assign to results of this expression*).

func simpleRandomSwap(rlmobjects:RLMResults!) -> RLMResults! {
    if (rlmobjects != nil && rlmobjects.count > 0) {

        let indexcount = Int(rlmobjects.count)

        for (var i=0 ; i<indexcount; i++) {
            let randomUInt:UInt = UInt(arc4random_uniform(UInt32(indexcount)))
            let myuint = UInt(i)


            // simple swap
            var temp = rlmobjects.objectAtIndex(myuint)
            rlmobjects.objectAtIndex(randomUInt) = rlmobjects.objectAtIndex(myuint)
            rlmobjects.objectAtIndex(myuint) = temp


        } // end for loop

    }


    return rlmobjects
}

Answer 1

First a quick note: RLMResults have no defined order unless they are sorted via RLMSortDescriptor.

Instead, to randomly sort you have two options:

1. Add a integer property to your object schema and assign random values to all the objects. You can then use a RLMSortDescriptor with RLMResults to sort the objects.

2. As mentioned in the comments above, copy the RLMObjects into an array and perform a random sort on this.

Here is an extension to RLMObject that does this:

extension RLMResults {
    public func toShuffledArray<T>(ofType: T.Type) -> [T] {

        var array = [T]()

        for result in self {
            if let result = result as? T {
                array.append(result)
            }
        }

        let count = array.count

        if count > 1 {
            for i in 0..<(count - 1) {
                let j = Int(arc4random_uniform(UInt32(count - i))) + Int(i)
                swap(&array[i], &array[j])
            }
        }

        return array
    }
}

You would call it like this:

let shuffled = results.toShuffledArray(TestObject.self)