Delete Duplicates and Sort Array of Objects in Objective-C

Arrays_Sort_Rem_Duplicates.m

NSOrderedSet *orderedSet = [NSOrderedSet orderedSetWithArray:_lastMessages];
NSArray *arrayWithoutDuplicates = [orderedSet array];

NSSortDescriptor *dateDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"date_" ascending:YES];
NSArray *sortDescriptors = [NSArray arrayWithObject:dateDescriptor];
NSArray *sortedEventArray = [arrayWithoutDuplicates sortedArrayUsingDescriptors:sortDescriptors];

_lastMessages = [sortedEventArray mutableCopy];