如何从 Swift 中的数组中获取最新日期

Question

I have an array of dates. I need to find the latest one. Can someone show me an example?

Answer 1

You can make NSDate conform to Comparable , as shown here

Given this, you can then use maxElement to find the maximum (ie the latest).

import Foundation

extension NSDate: Comparable { }

public func ==(lhs: NSDate, rhs: NSDate) -> Bool {
    return lhs.isEqualToDate(rhs)
}

public func <(lhs: NSDate, rhs: NSDate) -> Bool {
    return lhs.compare(rhs) == .OrderedAscending
}

let dates = [NSDate(), NSDate()]

let maxDate = maxElement(dates)

Note, maxElements goes bang for empty arrays so you may want to guard it with isEmpty :

let maxDate = dates.isEmpty ? nil : Optional(maxElement(dates))

Or, if you don't want to go the extension route:

if let fst = dates.first {
    let maxDate = dropFirst(dates).reduce(fst) {
        $0.laterDate($1)
    }
}

or, to return an optional:

let maxDate = dates.reduce(nil) {
  (lhs: NSDate?, rhs: NSDate?)->NSDate? in
    lhs.flatMap({rhs?.laterDate($0)}) ?? rhs
}

Answer 2

You can make use of reduce :

guard let dates = dates, !dates.isEmpty else { return nil }
dates.reduce(Date.distantPast) { $0 > $1 ? $0 : $1 }

Edit: Handle empty or nil array

Answer 3

Swift has Array methods for getting both the min and max values for dates.

You can use the following:

• let maxDate = myArrayOfDates.max()
• let minDate = myArrayOfDates.min()

So if you have an array of dates like so:

And here is the code if you want to copy it:

let now = Date()

let dates = [
    now,
    now.addingTimeInterval(120),
    now.addingTimeInterval(60)
]

let sut = dates.max()
print(sut!)

Hope this helps someone!

Answer 4

Run this in your playground

 var dates = [NSDate]() let dateFormatter = NSDateFormatter() dateFormatter.dateFormat = "dd-MM-yyyy" let date1 = dateFormatter.dateFromString("02-06-1987") let date2 = dateFormatter.dateFromString("02-06-2001") let date3 = dateFormatter.dateFromString("02-06-2010") //var date1 = NSDate() dates.append(date3!) dates.append(date1!) dates.append(date2!) var maxDate = dates[0] for i in 0...dates.count-1 { if(maxDate.compare(dates[i]).rawValue == -1){ maxDate = dates[i] println(maxDate) } println(maxDate) } println(maxDate.description)

have a good day :)