How to sort an array dates in swift 4 - ios

Question

I have an array of dates like this :-
var dateArray = ["2016-04-20", "2016-04-22", "2016-04-25", "2016-04-30"]
and I want to find out the difference of days between them. I do some research and i am able to do that with only two dates here is the approach i did in finding the difference between two date
let dateFormatter = DateFormatter()
let isoDate = "2016-04-20"
let calendar = NSCalendar.current
let currentDate = Date()
And in my viewDidLoad method I did this
override func viewDidLoad() {
super.viewDidLoad()
// let components = calendar.dateComponents([.day], from: )
dateFormatter.dateFormat = "yyyy-MM-dd"
dateFormatter.locale = Locale(identifier: "en_US_POSIX") //en_US_POSIX
let formatedStartDate = dateFormatter.date(from: isoDate)
let date = dateArray.compactMap { dateFormatter.date(from: $0) } // for date array
print(date)
let components = Set<Calendar.Component>([.day])
let differenceOfDate = Calendar.current.dateComponents(components, from: formatedStartDate!, to: currentDate )
print (differenceOfDate)
apiData()
}
As you can see in the code i created a constant let isoDate = "2016-04-20" and changed into formatedStartDate and find the difference between form this date to current date then it worked. But what if I have my own array of dates and how can i find the difference of my own array of dates and sort it into increasing or decreasing order. Please help?

Answer 1

Create the date formatter
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
dateFormatter.locale = Locale(identifier: "en_US_POSIX") //en_US_POSIX
Map the date string array to Date instances
let dateStringArray = ["2016-04-20", "2016-04-22", "2016-04-25", "2016-04-30"]
let dateArray = dateStringArray.map {dateFormatter.date(from: $0)!} // add .sorted() if the array is unordered.
In a loop get the differences between adjacent items
var differences = [Int]()
for i in 0..<dateArray.count - 1 {
let dayComponent = Calendar.current.dateComponents([.day], from: dateArray[i], to: dateArray[i+1])
differences.append(dayComponent.day!)
}
print(differences)

Answer 2

I'm not sure if you only want to compare the dates next to each other or compare each and every date. In the first case go with vadians solution. In the other case you can do something like this:
let dateStrings = ["2016-04-20", "2016-04-22", "2016-04-25", "2016-04-30"]
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
let dates = dateStrings.compactMap { dateFormatter.date(from: $0) }
let calendar = Calendar.current
var differences: [Int] = []
for i in 0..<dates.count {
for j in i + 1..<dates.count {
if let difference = calendar.dateComponents([.day], from: dates[i], to: dates[j]).day {
differences.append(difference)
}
}
}
let descendingDifferences = differences.sorted(by: >)
print(descendingDifferences) // results in [10, 8, 5, 5, 3, 2]