Replacement of date object with “today” and “yesterday” strings in iphone

I want to return my date objects with string “today” and “yesterday” and dates in Objective C.Please all comments are welcome:

I have dates with format @"yyyy-MM-dd HH:mm:ss"] and then figures out if the date is today or yesterday and than, if it is, it returns "(Yesterday | Today | Date ) " formated string.