How to round double to 2 decimal places and remove trailing zeros?

Question

I couldn't find a way to round double to 2 decimal places and remove trailing zeros in Dart. I found a way to round but it doesn't work if I try to truncate trailing zero.

Here is what I am trying to do:

double x = 5.0;
double y = 9.25843223423423;
double z = 10.10;

print(x); //Expected output --> 5
print(y); //Expected output --> 9.26
print(z); //Expected output --> 10.1

EDIT:

I found a way to solve the first 2 print statements above. I thought I should add it for whoever is searching it.

String getFormattedNumber( num ) {

  var result;
  if(num % 1 == 0) {
    result = num.toInt();
  } else {
    result = num.toStringAsFixed(2);
  }
return result.toString();

}

jamesdlin · Answer 1 · 2021-04-06T02:08:06.370

Rounding a floating point number according to a decimal representation doesn't make much sense since many decimal fractions (such as 0.3) can't be exactly represented by floating point numbers anyway. (This is inherent to all floating point numbers and is not specific to Dart.)

You can, however, try to make string representations of your number pretty. num.toStringAsFixed rounds to the specified number of fractional digits. From there, you can use a regular expression to remove trailing zeroes:

String prettify(double d) =>
    // toStringAsFixed guarantees the specified number of fractional
    // digits, so the regular expression is simpler than it would need to
    // be for more general cases.
    d.toStringAsFixed(2).replaceFirst(RegExp(r'\.?0*$'), '');

double x = 5.0;
double y = 9.25843223423423;
double z = 10.10;

print(prettify(x)); // Prints: 5
print(prettify(y)); // Prints: 9.26
print(prettify(z)); // Prints: 10.1

print(prettify(0)); // Prints: 0
print(prettify(1)); // Prints: 1
print(prettify(200); // Prints: 200

Also see How to remove trailing zeros using Dart.

This one is working correct than the one you mentioned other one — RuslanBek, Jan 19 '22 at 09:38

KuKu · Answer 2 · 2021-04-06T02:07:46.073

1

Here is sample code what you want.

multiply by 10^(count of number after point)
if count of number after point is 2
9.25843223423423 -> 925.843223423423
round 1)'s result
925.843223423423 -> 926
divide by 10^(count of number after point)
926 -> 9.26


import 'dart:math';

void main() {
  double x = 0.99;
  double y = 9.25843223423423;
  double z = 10.10;

  print(x); //Expected output --> 5
  print(y); //Expected output --> 9.26
  print(z); //Expected output --> 10.1
  
  print(customRound(x, 2));
  print(customRound(y, 2));
  print(customRound(z, 2));
  
  for(var i = 0.01 ; i < 1 ; i += 0.01) {
    print(customRound(i, 2));
  }
}

dynamic customRound(number, place) {
  var valueForPlace = pow(10, place);
  return (number * valueForPlace).round() / valueForPlace;
}

edited Apr 06 '21 at 02:07

answered Apr 06 '21 at 01:02

KuKu

6,654
1
13
25

1

This does not work for most floating-point values. Try it with all the values for 0.01 to 0.99 incrementing by 0.01. Failure rate is over 90%. – user207421 Apr 06 '21 at 01:59
@user207421 Hm... let me know what it is wrong with changed code that tested with from 0.01 to 0.99. – KuKu Apr 06 '21 at 02:08
What is wrong is that you are *printing* with restricted precision. The floating point *values* have more in the cases I refer to. This is inevitable because base-10 and base-20 are incommensurable. – user207421 Apr 07 '21 at 02:30

score 0 · Answer 3 · answered May 05 '23 at 05:05

I think a better way is using the Flutter maths library.

// ROUND NUMBERS TO 2 DECIMAL PLACES
  double roundNumber(double value, int places) {
    num val = pow(10.0, places);
    return ((value * val).round().toDouble() / val);
  }

This function would help you do for any decimal place you want.

Then you can use it this way:

double num1 = roundNumber(12.334456789, 2);
print(num1);

should print: : 12.33

How to round double to 2 decimal places and remove trailing zeros?

3 Answers3