Question

Here’s the scenario…

I have several float attributes in my data model which I want to compare against a number of variables (actually the same attributes in another object) and return if any match… straight forward NSPredicate.

However… what I would like to do is to keep track of which of those comparisons evaluate to true and then do a count. I then want to return only the top X results, i.e. those where the most comparisons are true.

Example… (not actual code!!)

object1.float1 = 1;
object1.float2 = 2;
object1.float3 = 3;

object2.float1 = 1;
object2.float2 = 2;
object2.float3 = 4;

object3.float1 = 1;
object3.float2 = 4;
object3.float3 = 4;

float1Variable = 1;
float2Variable = 2;
float3Variable = 3;

kReturnedObjects = 2;

I only want to retrieve object1 and object2.

Any help would be much appreciated, most of my possible solutions so far are incredibly laborious!

Answer 1

What I’d do is define some kind of evaluation-function to calculate the “similarity” of the objects. I.e

s(obj, comparison_obj) := (obj.var1 == comparison_obj.var1) + (obj.var2 == comparison_obj.var2) + (obj.var3 == comparison_obj.var3)

The larger s(obj, comparison_obj) is, the more variables are the same. You can then use Core Data to give you the list of kReturnedObjects objects, sorted by s descending.