Getting the decimal part of a double in Swift

Question

I'm trying to separate the decimal and integer parts of a double in swift. I've tried a number of approaches but they all run into the same issue...

let x:Double = 1234.5678 let n1:Double = x % 1.0           // n1 = 0.567800000000034 let n2:Double = x - 1234.0        // same result let n3:Double = modf(x, &integer) // same result 

Is there a way to get 0.5678 instead of 0.567800000000034 without converting to the number to a string?

Answer 1

You can use truncatingRemainder and 1 as the divider.

Returns the remainder of this value divided by the given value using truncating division.

Apple doc

Example:

let myDouble1: Double = 12.25 let myDouble2: Double = 12.5 let myDouble3: Double = 12.75  let remainder1 = myDouble1.truncatingRemainder(dividingBy: 1) let remainder2 = myDouble2.truncatingRemainder(dividingBy: 1) let remainder3 = myDouble3.truncatingRemainder(dividingBy: 1)  remainder1 -> 0.25 remainder2 -> 0.5 remainder3 -> 0.75 

Answer 2

Same approach as Alessandro Ornano implemented as an instance property of FloatingPoint protocol:

Xcode 11 • Swift 5.1

import Foundation  extension FloatingPoint {     var whole: Self { modf(self).0 }     var fraction: Self { modf(self).1 } } 

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1.2.whole    // 1 1.2.fraction // 0.2 

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If you need the fraction digits and preserve its precision digits you would need to use Swift Decimal type and initialize it with a String:

extension Decimal {     func rounded(_ roundingMode: NSDecimalNumber.RoundingMode = .plain) -> Decimal {         var result = Decimal()         var number = self         NSDecimalRound(&result, &number, 0, roundingMode)         return result     }     var whole: Decimal { rounded(sign == .minus ? .up : .down) }     var fraction: Decimal { self - whole } } 

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let decimal = Decimal(string: "1234.99999999")!  // 1234.99999999 let fractional = decimal.fraction                // 0.99999999 let whole = decimal.whole                        // 1234 let sum = whole + fractional                     // 1234.99999999  let negativeDecimal = Decimal(string: "-1234.99999999")!  // -1234.99999999 let negativefractional = negativeDecimal.fraction         // -0.99999999 let negativeWhole = negativeDecimal.whole                 // -1234 let negativeSum = negativeWhole + negativefractional      // -1234.99999999