Handy tool for sorting/grouping an array of items with dates into various calendar based groupings.

gistfile1.m

+ (NSArray*)eventsGroupedByDay:(NSArray*)events {
    return [HistoryManager events:events groupedByDateComponents:(NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit)];
}

+ (NSArray*)eventsGroupedByWeek:(NSArray*)events {
    return [HistoryManager events:events groupedByDateComponents:(NSWeekCalendarUnit|NSMonthCalendarUnit|NSYearCalendarUnit)];
}

+ (NSArray*)events:(NSArray*)events groupedByDateComponents:(NSUInteger)dateComponents {
    NSCalendar *gregorian = [[NSCalendar alloc]
                             initWithCalendarIdentifier:NSGregorianCalendar];
    
    NSMutableDictionary *groups = [NSMutableDictionary dictionary];
    NSDictionary *currentGroup;
    NSMutableArray *currentGroupEvents;
    
    for (Event* event in events) {
        NSDateComponents *components = [gregorian components:dateComponents
                                                    fromDate:event.date];
        NSDate *key = [gregorian dateFromComponents:components];
        currentGroup = groups[key];
        
        //If day doesn't exist, add new group
        if (!currentGroup) {
            currentGroupEvents = [NSMutableArray array];
            currentGroup = [@{  @"date":key,
                                @"events":currentGroupEvents} mutableCopy];
            [groups setObject:currentGroup forKey:key];
        }
        else {
            currentGroupEvents = currentGroup[@"events"];
        }
        
        //Add object to group
        [currentGroupEvents addObject:event];
        
    }
    
    NSArray *sortedKeys = [[NSArray arrayWithArray:[groups allKeys]] sortedArrayUsingSelector:@selector(compare:)];
    NSMutableArray *groupsArray = [NSMutableArray array];
    
    for (NSDate* groupKey in sortedKeys) {
        [groupsArray addObject:groups[groupKey]];
    }
    
    return groupsArray;
}