Filter items to section - swift

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?

Answer 1

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()

Answer 2

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"
}

Answer 3

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]