ios - Core data filtering -

i have core data structure follows:

business <-------->> employee <-------->> address

each business has multiple employees , each employee can have multiple addresses.

from business object, want able nsarray or nsset of address objects specify condition. e.g. street names have unique.

i know override isequal: i'm guessing going have unintended results. otherwise, have been looking using valueforkeypath:@"@distinctunionofobjects", don't think can pass condition.

here code have far:

    nsmutablearray *addressarray = [nsmutablearray array];     nsarray *employees = [employee sortedarray];      //loop through employees     (employee *employee in employees) {         (address *address in employee.addresses) {             [addressarray addobject:address];         }     }      //filter out duplicates     addressarray = [addressarray valueforkeypath:@"@distinctunionofobjects.city"]; 

this code gives me list of unique cities, however, want collection containing address objects have unique city values (or other condition).

i found way linqtoobjectivec library:

nsarray* addresseswithuniquecities = [input distinct:^id(id address) {     return [address city]; }]; 

looking @ source, underlying implementation follows:

typedef id (^selector)(id item);  -(nsarray *)distinct:(selector)keyselector {     nsmutableset* keyvalues = [[nsmutableset alloc] init];     nsmutablearray* distinctset = [[nsmutablearray alloc] init];     (id item in self) {         id keyforitem = keyselector(item);         if (![keyvalues containsobject:keyforitem]) {             [distinctset addobject:item];             [keyvalues addobject:keyforitem];         }     }     return distinctset;  } 

my final code ended being:

    nsmutablearray *addressarray = [nsmutablearray array];     nsarray *employees = [employee sortedemployees];      //loop through employees     (employee *employee in employees) {         (address *address in employee.addresses) {             [addressarray addobject:address];         }     }      //filter out duplicates     nsarray *distinctaddressarray = [addressarray distinct:^id(id address) {         return [address addressline];     }];      return distinctaddressarray;