I'm my app I have an NSMutableArray, and each entry has an NSMutableDictionary with several Key-Value pairs. One of these pairs contains the date of the entry. For one of the functions of my app I need to determine which entries are exactly 1 week apart from each other (i.e from Sunday to Saturday) and sum the data from one of the Key-Value pairs for each day of that week. How should I go about doing this?