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    With totalWorkTime being an NSTimeInterval  double  in second   totalWorkTimeInHours will give me the hours  but it gives me the amount of time in such a long precise number e g  1 543240952039        How do I round this down to  say  1 543 when I print totalWorkTimeInHours

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I would use  print String format     3f   totalWorkTimeInHours     and change  3f to any number of decimal numbers you need

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This is more flexible algorithm of rounding to N significant digits  Swift 3 solution   extension Double      Rounds the double to  places  significant digits   func roundTo places Int  - gt  Double       guard self    0 0 else           return 0           let divisor   pow 10 0  Double places  - ceil log10 fabs self         return  self   divisor  rounded     divisor            Double 0 123456789  roundTo places  2    0 12    Double 1 23456789  roundTo places  2    1 2    Double 1234 56789  roundTo places  2    1200

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To avoid Float imperfections use Decimal  extension Float       func rounded rule  NSDecimalNumber RoundingMode  scale  Int  - gt  Float           var result  Decimal   0         var decimalSelf   NSNumber value  self  decimalValue         NSDecimalRound  amp result   amp 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

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round a double value to x number of decimal  NO  of digits after decimal  var x   1 5657676754 var y    x 10000  rounded   10000 print y      1 5658      var x   1 5657676754  var y    x 100  rounded   100 print y      1 57      var x   1 5657676754 var y    x 10  rounded   10 print y      1 6

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In Swift 5 3 and Xcode 12  let pi  Double   3 14159265358979 String format  quot   2f quot   pi   Example    PS   It still the same since Swift 2 0 and Xcode 7 2

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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

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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

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The best way to format a double property is to use the Apple predefined methods    mutating func round   rule  FloatingPointRoundingRule    FloatingPointRoundingRule is a enum which has following possibilities  Enumeration Cases    case awayFromZero Round to the closest allowed value whose magnitude is greater than or equal to that of the source   case down Round to the closest allowed value that is less than or equal to the source   case toNearestOrAwayFromZero Round to the closest allowed value  if two values are equally close  the one with greater magnitude is chosen   case toNearestOrEven Round to the closest allowed value  if two values are equally close  the even one is chosen   case towardZero Round to the closest allowed value whose magnitude is less than or equal to that of the source   case up Round to the closest allowed value that is greater than or equal to the source   var aNumber   Double   5 2 aNumber rounded  up     6 0

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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  - gt  Decimal           var decimalValue   Decimal self          var result   Decimal           NSDecimalRound  amp result   amp 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

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if you want after the comma there is only 0 for the round  look at this example below   extension Double       func isInteger   - gt  Any           let check   floor self     self         if check               return Int self            else               return self                    let toInt  Double   10 0 let stillDouble  Double   9 12  print toInt isInteger     10 print stillDouble isInteger     9 12

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Extension for Swift 2  A more general solution is the following extension  which works with Swift 2  amp  iOS 9   extension Double           Rounds the double to decimal places value     func roundToPlaces places Int  - gt  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  - gt  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

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extension String    var roundedValue String        return String format     3f   self       Usage     totalWorkTimeInHours roundedValue

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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

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Use the built in Foundation Darwin library  SWIFT 3  extension Double       func round to places  Int  - gt  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

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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  extension Double        func truncate to places  Int  - gt  Double       return Double Int  pow 10  Double places     self  rounded       pow 10  Double places

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Swift 4  Xcode 10  yourLabel text    String format    2f   yourDecimalValue

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I found this wondering if it is possible to correct a user s input  That is if they enter three decimals instead of two for a dollar amount   Say 1 111 instead of 1 11 can you fix it by rounding   The answer for many reasons is no   With money anything over i e  0 001 would eventually cause problems in a real checkbook   Here is a function to check the users input for too many values after the period  But which will allow 1   1 1 and 1 11    It is assumed that the value has already been checked for successful conversion from a String to a Double     func need to be where transactionAmount text is in scope  func checkDoublesForOnlyTwoDecimalsOrLess  - gt Bool        var theTransactionCharacterMinusThree  Character    A      var theTransactionCharacterMinusTwo  Character    A      var theTransactionCharacterMinusOne  Character    A       var result   false      var periodCharacter Character             var myCopyString   transactionAmount text       if myCopyString containsString                  if  myCopyString characters count  gt   3                           theTransactionCharacterMinusThree   myCopyString myCopyString endIndex advancedBy -3                       if  myCopyString characters count  gt   2               theTransactionCharacterMinusTwo   myCopyString myCopyString endIndex advancedBy -2                      if  myCopyString characters count  gt  1               theTransactionCharacterMinusOne   myCopyString myCopyString endIndex advancedBy -1                         if  theTransactionCharacterMinusThree     periodCharacter                                result   true                       if theTransactionCharacterMinusTwo    periodCharacter                result   true                      if theTransactionCharacterMinusOne    periodCharacter                result   true                 else              if there is no period and it is a valid double it is good                   result   true             return result

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You can use Swift s round function to accomplish this   To round a Double with 3 digits precision  first multiply it by 1000  round it and divide the rounded result by 1000   let x   1 23556789 let y   Double round 1000 x  1000  print y      1 236   Other than any kind of printf      or String format       solutions  the result of this operation is still of type Double   EDIT  Regarding the comments that it sometimes does not work  please read this    What Every Programmer Should Know About Floating-Point Arithmetic

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This is a sort of a long workaround  which may come in handy if your needs are a little more complex  You can use a number formatter in Swift   let numberFormatter  NSNumberFormatter         let nf   NSNumberFormatter       nf numberStyle    DecimalStyle     nf minimumFractionDigits   0     nf maximumFractionDigits   1     return nf       Suppose your variable you want to print is   var printVar   3 567   This will make sure it is returned in the desired format   numberFormatter StringFromNumber printVar    The result here will thus be  3 6   rounded   While this is not the most economic solution  I give it because the OP mentioned printing  in which case a String is not undesirable   and because this class allows for multiple parameters to be set

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With Swift 5  according to your needs  you can choose one of the 9 following styles in order to have a rounded result from a Double      1  Using FloatingPoint rounded   method  In the simplest case  you may use the Double rounded   method   let roundedValue1    0 6844   1000  rounded     1000 let roundedValue2    0 6849   1000  rounded     1000 print roundedValue1     returns 0 684 print roundedValue2     returns 0 685      2  Using FloatingPoint rounded     method  let roundedValue1    0 6844   1000  rounded  toNearestOrEven    1000 let roundedValue2    0 6849   1000  rounded  toNearestOrEven    1000 print roundedValue1     returns 0 684 print roundedValue2     returns 0 685      3  Using Darwin round function  Foundation offers a round function via Darwin   import Foundation  let roundedValue1   round 0 6844   1000    1000 let roundedValue2   round 0 6849   1000    1000 print roundedValue1     returns 0 684 print roundedValue2     returns 0 685      4  Using a Double extension custom method built with Darwin round and pow functions  If you want to repeat the previous operation many times  refactoring your code can be a good idea   import Foundation  extension Double       func roundToDecimal   fractionDigits  Int  - gt  Double           let multiplier   pow 10  Double fractionDigits           return Darwin round self   multiplier    multiplier          let roundedValue1   0 6844 roundToDecimal 3  let roundedValue2   0 6849 roundToDecimal 3  print roundedValue1     returns 0 684 print roundedValue2     returns 0 685      5  Using NSDecimalNumber rounding accordingToBehavior   method  If needed  NSDecimalNumber offers a verbose but powerful solution for rounding decimal numbers   import Foundation  let scale  Int16   3  let behavior   NSDecimalNumberHandler roundingMode   plain  scale  scale  raiseOnExactness  false  raiseOnOverflow  false  raiseOnUnderflow  false  raiseOnDivideByZero  true   let roundedValue1   NSDecimalNumber value  0 6844  rounding accordingToBehavior  behavior  let roundedValue2   NSDecimalNumber value  0 6849  rounding accordingToBehavior  behavior   print roundedValue1     returns 0 684 print roundedValue2     returns 0 685      6  Using NSDecimalRound           function  import Foundation  let scale   3  var value1   Decimal 0 6844  var value2   Decimal 0 6849   var roundedValue1   Decimal   var roundedValue2   Decimal    NSDecimalRound  amp roundedValue1   amp value1  scale  NSDecimalNumber RoundingMode plain  NSDecimalRound  amp roundedValue2   amp value2  scale  NSDecimalNumber RoundingMode plain   print roundedValue1     returns 0 684 print roundedValue2     returns 0 685      7  Using NSString init format arguments   initializer  If you want to return a NSString from your rounding operation  using NSString initializer is a simple but efficient solution   import Foundation  let roundedValue1   NSString format     3f   0 6844  let roundedValue2   NSString format     3f   0 6849  print roundedValue1     prints 0 684 print roundedValue2     prints 0 685      8  Using String init format     initializer  Swift   s String type is bridged with Foundation   s NSString class  Therefore  you can use the following code in order to return a String from your rounding operation   import Foundation  let roundedValue1   String format     3f   0 6844  let roundedValue2   String format     3f   0 6849  print roundedValue1     prints 0 684 print roundedValue2     prints 0 685      9  Using NumberFormatter  If you expect to get a String  from your rounding operation  NumberFormatter offers a highly customizable solution   import Foundation  let formatter   NumberFormatter   formatter numberStyle   NumberFormatter Style decimal formatter roundingMode   NumberFormatter RoundingMode halfUp formatter maximumFractionDigits   3  let roundedValue1   formatter string from  0 6844  let roundedValue2   formatter string from  0 6849  print String describing  roundedValue1      prints Optional  0 684   print String describing  roundedValue2      prints Optional  0 685

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A handy way can be the use of extension of type Double  extension Double       var roundTo2f  Double  return Double round 100  self  100         var roundTo3f  Double  return Double round 1000 self  1000        Usage   let regularPie   Double   3 14159 var smallerPie   Double   regularPie roundTo3f     results 3 142 var smallestPie  Double   regularPie roundTo2f     results 3 14

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In Swift 3 0 and Xcode 8 0     extension Double       func roundTo places  Int  - gt  Double           let divisor   pow 10 0  Double places           return  self   divisor  rounded     divisor           Use this extension like so   let doubleValue   3 567 let roundedValue   doubleValue roundTo places  2  print roundedValue     prints 3 56

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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

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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

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Not Swift but I m sure you get the idea   pow10np   pow 10 num places   val   round val pow10np    pow10np

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Building on Yogi s answer  here s a Swift function that does the job   func roundToPlaces value Double  places Int  - gt  Double       let divisor   pow 10 0  Double places       return round value   divisor    divisor

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var n   123 111222333 n   Double Int n   10 0     10 0  Result  n   123 1 Change 10 0  1 decimal place  to any of 100 0  2 decimal place   1000 0  3 decimal place  and so on  for the number of digits you want after decimal

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Either    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  - gt  Double           return Double String format       n f   self              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  - gt  Double           let multiplier   pow 10  Double n           return  multiplier   self  rounded   multiplier

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This is a fully worked code  Swift 3 0 4 0 5 0   Xcode 9 0 GM 9 2 and above  let doubleValue   Double   123 32565254455 self lblValue text   String format    f   doubleValue  print self lblValue text    output - 123  let doubleValue   Double   123 32565254455 self lblValue 1 text   String format    1f   doubleValue  print self lblValue 1 text    output - 123 3  let doubleValue   Double   123 32565254455 self lblValue 2 text   String format    2f   doubleValue  print self lblValue 2 text    output - 123 33  let doubleValue   Double   123 32565254455 self lblValue 3 text   String format    3f   doubleValue  print self lblValue 3 text    output - 123 326

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

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