For Swift4 to get weekday from string
func getDayOfWeek(today:String)->Int {
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd"
let todayDate = formatter.date(from: today)!
let myCalendar = NSCalendar(calendarIdentifier: NSCalendar.Identifier.gregorian)!
let myComponents = myCalendar.components(NSCalendar.Unit.weekday, from: todayDate)
let weekDay = myComponents.weekday
return weekDay!
}
let weekday = getDayOfWeek(today: "2018-10-10")
print(weekday) // 4