CODEWITHSUNDEEP
iosobjective-ccomparensmanagedobject
Denis Balko
Denis Balko

Reputation: 1596

Find NSManagedObjects from an NSArray that share a property

I have a fairly large number of NSManagedObjects in an NSArray and need to check whether do any of them have the same value for a property. The obvious way is nested for loops however it will take ages to go through all of them as there are about a 1000 objects in the array.

for (NSManagedObject *object in array) {
    for (NSManagedObject *secondObject in array {
        if ([[object valueForKey:@"key"] isEqualTo:[secondObject valueForKey:@"key"]] &&
           object != secondObject) {
            NSLog(@"Sharing a property");
        }
    }
}

Any better way to do this? If there are 1000 objects that accounts to 1 000 000 comparisons, that might take some time.

Upvotes: 0

Views: 616

Answers (3)

Arek Holko
Arek Holko

Reputation: 9006

You could use an NSDictionary. Each entry would be made from the following pair:

  • key would be equal to the selected NSManagedObjects attribute
  • value would be an NSArray of NSManagedObjects, that share this attribute's value

Upvotes: 4

jscs
jscs

Reputation: 64002

Get the list of key values for the objects in the array, then turn that into a set. If the size of the set is the same as that of the original array, there are no matches.

If you need to know which objects match, use a dictionary to create a multiset -- each key has an array of the objects as its value.

Creating your own keyed set class is also an option.

Upvotes: 3

Martin R
Martin R

Reputation: 539725

You can sort the array according to the values of that property. Then a single loop over the array is sufficient to find objects sharing the same value of the property.

Upvotes: 2

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