Reusable method to check if all objects are unequal using valueForKey - objective-c

Question

I have been working with this method for hours. It is supposed to simply check if the attribute of the cards passed in as otherCards isEqual to the same attribute of this (self) instance of class. But I am tearing my hair out - it is giving false results
(BOOL)otherCards: (NSArray *)otherCards allHaveUnequalAttribute: (NSString *)key
{
NSArray *values = [NSArray arrayWithArray:[otherCards valueForKey:key]];
int countUnequalMatches = 0;
for (NSNumber *setValue in values) {
if (![[self valueForKey:key] isEqual:setValue]) {
countUnequalMatches++;}
}
NSLog(#"countUnequalMatches %d values count: %d", countUnequalMatches, [values count]);
if (countUnequalMatches == [values count]) return YES ?: NO;
}
It is called like this:
if ([self otherCards:otherCards allHaveUnequalAttribute:CARD_SHAPE]) {
NSLog(#"All unequal");
} else {
NSLog(#"One or more card equal");
}

Answer 1

I found the bug myself
if (countUnequalMatches == [values count]) return YES ?: NO;
should be:
if (countUnequalMatches == [otherCards count]) return YES ?: NO;
as I used the Set as an way to count unique items.

Answer 2

This is the sort of thing that predicates are very well suited to handle.
-(BOOL)otherCards: (NSArray *)otherCards allHaveUnequalAttribute: (NSString *)key
{
NSPredicate *pred = [NSPredicate predicateWithFormat:#"%K == %#", key, [self valueForKey:key]];
NSArray *equalCards = [otherCards filteredArrayUsingPredicate:pred];
return equalCards.count == 0;
}