Add objects to NSMutable array with grouping

Question

I want my NSArray sampleData to receive actual data from parse.com database assuming like this:

self.sampleData = @[ @{ @"date": @"12/5/2014",
                        @"group": @[ @{ @"text": @"post1", @"location": @"x,y" },
                                     @{ @"text": @"post2", @"location": @"x,y" },
                                     @{ @"text": @"post3", @"location": @"x,y" },
                                     @{ @"text": @"post4", @"location": @"x,y" },
                                     @{ @"text": @"post5", @"location": @"x,y" }
                                   ]
                        },
                     @{ @"date": @"12/3/2014",
                        @"group": @[ @{ @"text": @"post6", @"location": @"x,y" },
                                     @{ @"text": @"post7", @"location": @"x,y" },
                                     @{ @"text": @"post8", @"location": @"x,y" },
                                     @{ @"text": @"post9", @"location": @"x,y" },
                                     @{ @"text": @"post10", @"location": @"x,y" }
                                   ]
                        }
                  ];

As you can see, I want to group text and location by date, so that I can display them in a view with date as header and text/location as content. Here below is what I'm capable doing so far:

PFQuery *postQuery = [PFQuery queryWithClassName:kPAWParsePostsClassKey];
[postQuery whereKey:kPAWParseUserKey equalTo:[PFUser currentUser]];

postQuery.cachePolicy = kPFCachePolicyNetworkElseCache;
postQuery.limit = 20;

[postQuery findObjectsInBackgroundWithBlock:^(NSArray *myPosts, NSError *error)
 {
     if( !error )
     {

         NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
         [formatter setDateFormat:@"MM/dd/yyyy"]; 

         NSMutableArray *objectArray = [NSMutableArray new];

         for (PFObject *object in myPosts) {
             [objectArray addObject:@{@"createdAt": [formatter stringFromDate:object.createdAt], @"text": [object objectForKey:@"text"], @"location": [object objectForKey:@"location"]}];
         }

         self.sampleData = objectArray;
         NSLog(@"My sampleData --> %@", self.sampleData);

     }
 }
];

The above code is obvious there's no grouping whatsoever, so really need help here.

Answer 1

Okay, so you have an array of items, and you want to group them into sections based on a particular key.

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"MM/dd/yyyy"];

// Sparse dictionary, containing keys for "days with posts"
NSMutableDictionary *daysWithPosts = [NSMutableDictionary dictionary];

[myPosts enumerateObjectsUsingBlock:^(PFObject *object, NSUInteger idx, BOOL *stop) {

    NSString *dateString = [formatter stringFromDate:[object createdAt]];

    // Check to see if we have a day already.
    NSMutableArray *posts = [daysWithPosts objectForKey: dateString];

    // If not, create it
    if (posts == nil || (id)posts == [NSNull null])
    {
        posts = [NSMutableArray arrayWithCapacity:1];
        [daysWithPosts setObject:posts forKey: dateString];
    }

    // add post to day
    [posts addObject:obj];
}];

// Sort Dictionary Keys by Date
NSArray *unsortedSectionTitles = [daysWithPosts allKeys];
NSArray *sortedSectionTitles = [unsortedSectionTitles sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    NSDate *date1 = [formatter dateFromString:obj1];
    NSDate *date2 = [formatter dateFromString:obj2];
    return [date2 compare:date1];
}];

NSMutableArray *sortedData = [NSMutableArray arrayWithCapacity:sortedSectionTitles.count];

// Put Data into correct format:
[sortedSectionTitles enumerateObjectsUsingBlock:^(NSString *dateString, NSUInteger idx, BOOL *stop) {
    NSArray *group = daysWithPosts[dateString];
    NSDictionary *dictionary = @{ @"date":dateString,
                                  @"group":group };
    [sortedData addObject:dictionary];
}];

self.sampleData = sortedData;

This code will not generate exactly what you asked for. It will generate something that looks like this:

sampleData = @[ @{ @"date": @"12/5/2014",
                    @"group": @@[ PFObject*,
                                 PFObject*,
                                 PFObject*,
                                 PFObject*,
                                 PFObject*,
                               ]
                    },
                 @{ @"date": @"12/3/2014",
                    @"group": @[ PFObject*,
                                 PFObject*,
                                 PFObject*,
                                 PFObject*,
                                 PFObject
                               ]
                    }
              ];

There's no need to convert your PFObject* in the myPosts array into @{ @"text": @"post5", @"location": @"x,y" } since you'll lose access to other pieces of information. Here is how you would use this sampleData array.

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView; {
    return self.sampleData.count;
}

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section; {
    return self.sampleData[section][@"date"];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section; {
    return self.sampleData[section][@"group"].count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath; {

    PFObject *post = self.sampleData[indexPath.section][@"group"][indexPath.row];
    UITableViewCell *cell = // dequeue A reusable tableviewcell here

    // configure the cell here

    return cell;
}