Filter items to section

Question

I want to filter items with property isCompleted = true to section with name Completed and non completed items to ToDo. How to render items?

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        if section == 0 {
            return manager.tasks.filter({$0.isCompleted == false}).count
        } else {
            return manager.tasks.filter({$0.isCompleted}).count
        }
    }

    override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
        switch section {
        case 0:
            return "ToDo"
        case 1:
            return "Completed"
        default:
            return nil
        }
    }

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: Keys.cell.rawValue, for: indexPath) as! ToDoCell

        let currentItem = manager.tasks[indexPath.row]
        cell.titleLabel.text = currentItem.taskName
        cell.descriptionLabel.text = currentItem.description
        if manager.tasks[indexPath.row].description?.isEmpty ?? false {
            cell.descLabelBottomConstraint.constant = 0
        }

        let accessoryType: UITableViewCell.AccessoryType = currentItem.isCompleted ? .checkmark : .none
        cell.accessoryType = accessoryType
        return cell
    }

I guess I need to filter items into two different arrays? But which way is the most correct?

`let currentItem = manager.tasks[indexPath.row]` is the problem. You are failing to distinguish completed items. The entire data model itself is wrong. A single simple array won’t work. — matt, Feb 27 '20 at 13:15

score 1 · Answer 1 · answered Feb 27 '20 at 12:51

You can create 2 properties completed and notCompleted in the Manager and use them as dataSource of the tableView.

class Manager {    
    lazy var completed: [Task] = {
        return tasks.filter({ !$0.isCompleted })
    }()
    lazy var notCompleted: [Task] = {
        return tasks.filter({ $0.isCompleted })
    }()
}

UITableViewDataSource and UITableViewDelegate methods,

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return section == 0 ? manager.notCompleted.count : manager.completed.count
}

func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
    return section == 0 ? "Todo" : "Completed"
}

vadian · Accepted Answer · 2020-02-27T13:21:09.377

Never filter things in numberOfRowsInSection. Don't do that, this method is called very often.

Create a model

struct Section {
    let title : String
    var items : [Task]
}

Declare the data source array
```
var sections = [Section]()
```

In viewDidLoad populate the array and reload the table view

sections = [Section(title: "ToDo", items: manager.tasks.filter{!$0.isCompleted}),
            Section(title: "Completed", items: manager.tasks.filter{$0.isCompleted})]
tableView.reloadData()

Now the datasource methods become very clean (and fast)

override func numberOfSections(in tableView: UITableView) -> Int {
    return sections.count
}

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

override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
    return sections[section].title
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: Keys.cell.rawValue, for: indexPath) as! ToDoCell

    let currentItem = sections[indexPath.section].items[indexPath.row]
    cell.titleLabel.text = currentItem.taskName
    cell.descriptionLabel.text = currentItem.description
    if currentItem.description?.isEmpty ?? false {
        cell.descLabelBottomConstraint.constant = 0
    } // you have to add an else clause to set the constraint to the default value

    cell.accessoryType = currentItem.isCompleted ? .checkmark : .none
    return cell
}

It would be still more efficient to filter the items O(n) with a partition algorithm

let p = manager.tasks.partition(by: { $0.completed })
sections = [Section(title: "ToDo", items: Array(manager.tasks[p...])),
            Section(title: "Completed", items: Array(manager.tasks[..<p]))]
tableView.reloadData()

Thread 1: Fatal error: Index out of range. In titleForHeaderInSection — SilentKunZ, Feb 27 '20 at 13:01
Of course you have to adjust `numberOfSections` and `cellForRow` accordingly — vadian, Feb 27 '20 at 13:02
How to edit my cellForRowAt? I attached the code to first message — SilentKunZ, Feb 27 '20 at 13:11
Yes, I just thought of it myself, thank you) And one more question how to make moving to a section in real time with animation? — SilentKunZ, Feb 27 '20 at 13:20
This is another question. There is an API to move items animated. First move the item in the data source then call this API. — vadian, Feb 27 '20 at 13:21

score 1 · Answer 3 · answered Feb 27 '20 at 12:52

You want your original dataSource to be an array of the 2 different arrays (one with completed and one that is not completed.) [[]]

I found This one that seems pretty solid. However, it returns an dictionary, but i rewrote it slightly for you:

extension Sequence {
    func group<U: Hashable>(by key: (Iterator.Element) -> U) -> [[Iterator.Element]] {
        return Dictionary.init(grouping: self, by: key).map({$0.value})
    }
}

This way when you are in title header or cellForRowAt you can call it by manager.task[indexPath.section][indexPath.item]

Filter items to section

3 Answers3