Create a struct for example

 struct Rate { let currency : String let date : Date var value : Double } 

Create an array var historicalRates = [Rate]().

In the for loop

calculate the date via Calendar and DateComponents, your way gets in trouble on overflow to the next month.

create a Date from the current date.

create a Rate instance with actual date and name, add it to the historicalRates and pass it to the asynchronous task.

Assign the rate value in the completion block.

Use DispatchGroup to get notified when the loop is finished.

Finally sort historicalRates by date.

Create a struct for example

 struct Rate { let currency : String let date : Date var value : Double } 

Create an array var historicalRates = [Rate]().

In the for loop

calculate the date with the Calendar API, your way gets in trouble on overflow to the next month. For example

 let calendar = Calendar.current // set the date to noon to avoid daylight saving changes at midnight in a few countries let today = calendar.date(bySettingHour: 12, minute: 0, second: 0, of: Date())! let formatter = DateFormatter() formatter.dateFormat = "yyyy-MM-dd" for dayOffset in 0...7 { let currentDate = calendar.date(byAdding: .day, value: dayOffset, to: today)! let currentDateAsString = formatter.string(from: currentDate) print(currentDate, currentDateAsString) } 

create a Date from the current date.

create a Rate instance with actual date and name, add it to the historicalRates and pass it to the asynchronous task.

Assign the rate value in the completion block.

Use DispatchGroup to get notified when the loop is finished.

Finally sort historicalRates by date.