How do you round a double in Dart to a given degree of precision AFTER the decimal point

Question

Given a double  I want to round it to a given number of points of precision after the decimal point  similar to PHP s round   function   The closest thing I can find in the Dart docs is double toStringAsPrecision    but this is not quite what I need because it includes the digits before the decimal point in the total points of precision   For example  using toStringAsPrecision 3    0 123456789 rounds to 0 123   9 123456789 rounds to 9 12   98 123456789 rounds to 98 1   987 123456789 rounds to 987   9876 123456789 rounds to 9 88e 3   As the magnitude of the number increases  I correspondingly lose precision after the decimal place

User · Answer

This works pretty well  var price 99 012334554 price   price roundTodouble    print price      99 01

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The modified answer of  andyw using Dart Extension methods   extension Precision on double       double toPrecision int fractionDigits            double mod   pow 10  fractionDigits toDouble             return   this   mod  round   toDouble     mod             Usage   var latitude   1 123456  var latitudeWithFixedPrecision   latitude toPrecision 3      Outputs  1 123

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You can use toStringAsFixed in order to display the limited digits after decimal points  toStringAsFixed returns a decimal-point string-representation  toStringAsFixed accepts an argument called fraction Digits which is how many digits after decimal we want to display  Here is how to use it  double pi   3 1415926  const val   pi toStringAsFixed 2      3 14

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Above solutions do not appropriately round numbers  I use   double dp double val  int places       double mod   pow 10 0  places       return   val   mod  round   toDouble     mod

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If you don t want any decimals when the resulting decimals are all zeroes  something like this would work  String fixedDecimals double d  int decimals   bool removeZeroDecimals   true      double mod   pow 10 0  decimals     double result     d   mod  round   toDouble     mod     if  removeZeroDecimals  amp  amp  result -  result truncate       0 0   decimals   0    return result toStringAsFixed decimals      This will simply output 9 instead of 9 00 if the input is 9 004 and you want 2 decimals

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double value   2 8032739273  String formattedValue   value toStringAsFixed 3

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Define an extension  extension Ex on double     double toPrecision int n    gt  double parse toStringAsFixed n       Usage  void main       double d   2 3456789    double d1   d toPrecision 1      2 3   double d2   d toPrecision 2      2 35   double d3   d toPrecision 3      2 345

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Just write this extension on double extension Round on double     double roundToPrecision int n        int fac   pow 10  n       return  this   fac  round     fac

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To round a double in Dart to a given degree of precision AFTER the decimal point  you can use built-in solution in dart toStringAsFixed   method  but you have to convert it back to double void main       double step1   1 3      print step1      0 3333333333333333      String step2   step1 toStringAsFixed 2      print step2      0 33       double step3   double parse step2     print step3      0 33

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var price   99 012334554  price   price toStringAsFixed 2   print price      99 01  That is the ref of dart  ref  https   api dartlang org stable 2 3 0 dart-core num toStringAsFixed html

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I think the accepted answer is not the perfect solution because it converts to string  If you don t wanna convert to string and back to a double use double toPrecision decimalNumber  from GetX package  If you don t wanna use GetX just for this  I highly recommend GetX  it will change your life with flutter  you can copy and paste this  import  dart math    extension Precision on double     double toPrecision int fractionDigits        var mod   pow 10  fractionDigits toDouble    toDouble        return   this   mod  round   toDouble     mod

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num toStringAsFixed   rounds  This one turns you num  n  into a string with the number of decimals you want  2   and then parses it back to your num in one sweet line of code  n   num parse n toStringAsFixed 2

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See the docs for num toStringAsFixed     String toStringAsFixed int fractionDigits   Returns a decimal-point string-representation of this   Converts this to a double before computing the string representation    If the absolute value of this is greater or equal to 10 21 then this methods returns an exponential representation computed by this toStringAsExponential       Examples   1000000000000000000000 toStringAsExponential 3      1 000e 21    Otherwise the result is the closest string representation with exactly fractionDigits digits after the decimal point  If fractionDigits equals 0 then the decimal point is omitted    The parameter fractionDigits must be an integer satisfying  0  lt   fractionDigits  lt   20   Examples   1 toStringAsFixed 3       1 000  4321 12345678  toStringAsFixed 3       4321 123  4321 12345678  toStringAsFixed 5       4321 12346 123456789012345678901 toStringAsFixed 3       123456789012345683968 000 1000000000000000000000 toStringAsFixed 3      1e 21 5 25 toStringAsFixed 0      5

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I used the toStringAsFixed   method  to round a number to specific numbers after the decimal point EX  double num   22 48132906  and when I rounded it to two numbers like this  print num toStringAsFixed 2      It printed 22 48 and when I rounded to one number  it printed  22 5

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Above solutions do not work for all cases  What worked for my problem was this solution that will round your number  0 5 to 1 or 0 49 to 0  and leave it without any decimals   Input  12 67  double myDouble   12 67  var myRoundedNumber     Note the  var  datatype     Here I used 1 decimal  You can use another value in toStringAsFixed x  myRoundedNumber   double parse  myDouble  toStringAsFixed 1    myRoundedNumber   myRoundedNumber round     print myRoundedNumber     Output  13  This link has other solutions too

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void main       int decimals   2    int fac   pow 10  decimals     double d   1 234567889    d    d   fac  round     fac    print  d   d        Prints  1 23

[dart] How do you round a double in Dart to a given degree of precision AFTER the decimal point?

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