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

If you want to round `Double` values, you might want to use Swift `Decimal` so you don't introduce any errors that can crop up when trying to math with these rounded values. If you use `Decimal`, it can accurately represent decimal values of that rounded floating point value.

So you can do:

extension Double {
/// Convert `Double` to `Decimal`, rounding it to `scale` decimal places.
///
/// - Parameters:
/// - scale: How many decimal places to round to. Defaults to `0`.
/// - mode: The preferred rounding mode. Defaults to `.plain`.
/// - Returns: The rounded `Decimal` value.

func roundedDecimal(to scale: Int = 0, mode: NSDecimalNumber.RoundingMode = .plain) -> Decimal {
var decimalValue = Decimal(self)
var result = Decimal()
NSDecimalRound(&result, &decimalValue, scale, mode)
return result
}
}

Then, you can get the rounded `Decimal` value like so:

let foo = 427.3000000002
let value = foo.roundedDecimal(to: 2) // results in 427.30

And if you want to display it with a specified number of decimal places (as well as localize the string for the user's current locale), you can use a `NumberFormatter`:

let formatter = NumberFormatter()
formatter.maximumFractionDigits = 2
formatter.minimumFractionDigits = 2

if let string = formatter.string(for: value) {
print(string)
}

[1]:

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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))`

//find the distance between two points
let coordinateSource = CLLocation(latitude: 30.7717625, longitude:76.5741449 )
let coordinateDestination = CLLocation(latitude: 29.9810859, longitude: 76.5663599)
let distanceInMeters = coordinateSource.distance(from: coordinateDestination)
let valueInKms = distanceInMeters/1000
let preciseValueUptoThreeDigit = Double(round(1000*valueInKms)/1000)
self.lblTotalDistance.text = "Distance is : \(preciseValueUptoThreeDigit) kms"

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
}
}

**Swift 4, Xcode 10**

yourLabel.text = String(format:"%.2f", yourDecimalValue)

> How do I round this down to, say, 1.543 **when I print** `totalWorkTimeInHours`?

To round `totalWorkTimeInHours` to 3 digits for printing, use the `String` constructor which takes a `format` string:

print(String(format: "%.3f", totalWorkTimeInHours))

You can add this extension :

extension Double {
var clean: String {
return self.truncatingRemainder(dividingBy: 1) == 0 ? String(format: "%.0f", self) : String(format: "%.2f", self)
}
}

and call it like this :

let ex: Double = 10.123546789
print(ex.clean) // 10.12

**Use the built in Foundation Darwin library**

SWIFT 3

extension Double {
func round(to places: Int) -> Double {
let divisor = pow(10.0, Double(places))
return Darwin.round(self * divisor) / divisor
}
}

Usage:

let number:Double = 12.987654321
print(number.round(to: 3))

Outputs: 12.988

This seems to work in Swift 5.

Quite surprised there isn't a standard function for this already.

//Truncation of Double to n-decimal places with rounding


~~~Swift
extension Double {

func truncate(to places: Int) -> Double {
return Double(Int((pow(10, Double(places)) * self).rounded())) / pow(10, Double(places))
}

}

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))
}
}