Question

I have an NSArray which contains NSDictionary objects with keys that are NSNumber objects. I would like to calculate the max value using valueForKeyPath. If I were using strings in the following example, I would use valueForKeyPath:@”@max.OHLCClose”. How do I do the same with NSNumber objects as keys?

typedef enum _OHLCField {
   OHLCOpen,
   OHLCClose
} OHLCField;

NSMutableArray *newData = [NSMutableArray array];

newData addObject: [NSDictionary dictionaryWithObjectsAndKeys: 
[NSDecimalNumber numberWithDouble:fOpen], [NSNumber numberWithInt:OHLCOpen], 
[NSDecimalNumber numberWithDouble:fClose], [NSNumber numberWithInt:OHLCClose]];

Answer 1

KVC requires keys to be strings:

A key is a string that identifies a specific property of an object. Typically, a key corresponds to the name of an accessor method or instance variable in the receiving object. Keys must use ASCII encoding, begin with a lowercase letter, and may not contain whitespace.

So the answer is unfortunately you can’t do this with valueForKeyPath:.

If you need to use NSNumber‘s as your keys you will have to code the algorithm yourself – just iterate over the array and find the maximum value associated with your key. You could wrap the algorithm in a category so it becomes “part” of NSArray.