OBJ-C：当key不是字符串时使用valueForKeyPath

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?I have an NSArray which contains NSDictionary o