Rounding a double value to x number of decimal places in swift

Question

Can anyone tell me how to round a double value to x number of decimal places in Swift?

I have:

var totalWorkTimeInHours = (totalWorkTime/60/60)


        

Answer 1

To avoid Float imperfections use Decimal

extension Float {
    func rounded(rule: NSDecimalNumber.RoundingMode, scale: Int) -> Float {
        var result: Decimal = 0
        var decimalSelf = NSNumber(value: self).decimalValue
        NSDecimalRound(&result, &decimalSelf, scale, rule)
        return (result as NSNumber).floatValue
    }
}

ex.
1075.58 rounds to 1075.57 when using Float with scale: 2 and .down
1075.58 rounds to 1075.58 when using Decimal with scale: 2 and .down

Answer 2

The code for specific digits after decimals is:

var a = 1.543240952039
var roundedString = String(format: "%.3f", a)

Here the %.3f tells the swift to make this number rounded to 3 decimal places.and if you want double number, you may use this code:

// String to Double

var roundedString = Double(String(format: "%.3f", b))

Answer 3

Here's one for SwiftUI if you need a Text element with the number value.

struct RoundedDigitText : View {
    let digits : Int
    let number : Double

    var body : some View {
        Text(String(format: "%.\(digits)f", number))
    }
}

Answer 4

Either:

1. Using String(format:):

   • Typecast Double to String with %.3f format specifier and then back to Double

     Double(String(format: "%.3f", 10.123546789))!
     

   • Or extend Double to handle N-Decimal places:

     extension Double {
         func rounded(toDecimalPlaces n: Int) -> Double {
             return Double(String(format: "%.\(n)f", self))!
         }
     }
     

2. By calculation

   • multiply with 10^3, round it and then divide by 10^3...

     (1000 * 10.123546789).rounded()/1000
     

   • Or extend Double to handle N-Decimal places:

     extension Double {    
         func rounded(toDecimalPlaces n: Int) -> Double {
             let multiplier = pow(10, Double(n))
             return (multiplier * self).rounded()/multiplier
         }
     }
     

Answer 5

extension String{
  var roundedValue:String {
     return String(format: "%.3f", self)
}}

Usage :

totalWorkTimeInHours.roundedValue

Answer 6

Extension for Swift 2

A more general solution is the following extension, which works with Swift 2 & iOS 9:

extension Double {
    /// Rounds the double to decimal places value
    func roundToPlaces(places:Int) -> Double {
        let divisor = pow(10.0, Double(places))
        return round(self * divisor) / divisor
    }
}

Extension for Swift 3

In Swift 3 round is replaced by rounded:

extension Double {
    /// Rounds the double to decimal places value
    func rounded(toPlaces places:Int) -> Double {
        let divisor = pow(10.0, Double(places))
        return (self * divisor).rounded() / divisor
    }
}

Example which returns Double rounded to 4 decimal places:

let x = Double(0.123456789).roundToPlaces(4)  // x becomes 0.1235 under Swift 2
let x = Double(0.123456789).rounded(toPlaces: 4)  // Swift 3 version