Group NSArray results by date for tableview sections

Question 1

NSMutableArray *dataSource = [NSMutableArray new];

// Sorting your array by date asc
array = [[array sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    YourObject *firstObject = obj1;
    YourObject *secondObject = obj2;

    return [secondObject.date compare:firstObject.date] == NSOrderedAscending;
}] mutableCopy];


int section = 0;
[dataSource addObject:[NSMutableArray array]]; //Adding first section

for (int i = 0; i < array.count - 1; i++) {
    YourObject *firstObject = array[i];
    YourObject *secondObject = array[i+1];

    NSDate *firstDate = [self dateWithoutTimePart:firstObject.date];
    NSDate *secondDate = [self dateWithoutTimePart:secondObject.date];

    NSMutableArray *sectionArray = dataSource[section];

    if (![sectionArray containsObject:firstObject]) {
        [sectionArray addObject:firstObject];
    }
    if (![firstDate compare:secondDate] == NSOrderedSame)
    {
        NSMutableArray *newSection = [NSMutableArray array];
        [newSection addObject:secondObject];
        [dataSource addObject:newSection];

        section++;
    }
}

// Adding last object to last section
[dataSource.lastObject addObject:array.lastObject];

This is a fast written code, so sorry for possible mistakes :)

Question 2

Here's the solution I use

class VC: UITableViewController {

var source: DataSource!
var monthList = [String]()
var monthDictionary = [String:[object]]()

override func viewDidLoad() {
    super.viewDidLoad()
    let nib = UINib(nibName: "ObjectCell", bundle: nil)
    tableView.register(nib, forCellReuseIdentifier: "ObjectCell")
    tableView.rowHeight = 60
    tableView.separatorColor = .clear
    organizeObjectsIntoSections() //The magic happens here!
}

func organizeObjectsIntoSections() {
    for object in source.object {
        if monthDictionary[object.date.monthString] == nil { // if you the dictionary does not have a key for that month, add it as an array
            monthDictionary[object.date.monthString] = [object]
        } else { // otherwise append it to the existing array
            monthDictionary[object.date.monthString]?.append(object)
        }
        if !monthList.contains(object.date.monthString) {
           monthList.append(object.date.monthString) 
        }
    }
    monthList = Array(monthDictionary.keys) // store the keys for easy reference

}


override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
    return monthList[section] // number of keys i.e. months in the data set
}

override func tableView(_ tableView: UITableView, willDisplayHeaderView view: UIView, forSection section: Int) {
    guard let header = view as? UITableViewHeaderFooterView else { return }
    header.backgroundView?.backgroundColor = .white
    header.textLabel?.font = UIFont(name: "Avenir-Heavy", size: 16)!
    header.textLabel?.textColor = .black
}

override func numberOfSections(in tableView: UITableView) -> Int {
    return monthList.count // number of months stored in the dictionary
}

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return monthDictionary[monthList[section]]!.count
}


override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    guard let cell = tableView.dequeueReusableCell(withIdentifier: "ObjectCell", for: indexPath) as? ObjectCell
        else { return UITableViewCell() }
    let selectedObject = objectAt(indexPath)
    cell.configure(withObject: selectedObject)

    return cell
}

func objectAt(_ indexPath: IndexPath) -> object {
    let month = monthList[indexPath.section]
    return ((monthDictionary[month]!) as [object])[indexPath.row]
}
}

Explanation:

Parse through the list and store objects in dictionaries based on their month
Store a list of those keys
Reference the object:
- by accessing the key for the section let key = monthList[indexPath.section]
- using that value to access the right object array let objectArray = monthDictionary[key].
- Finally, get the object by subscripting the array objectArray[indexPath.row]