How to format numbers as thousands separators in Dart

You can use NumberFormat passing a custom format in ICU formatting pattern, take a look in NumberFormat.

import 'package:intl/intl.dart';

void main() {
  var formatter = NumberFormat('#,##,000');
  print(formatter.format(16987));
  print(formatter.format(13876));
  print(formatter.format(456786));
}

Output

16,987
13,876
4,56,786

I found NumberFormat class from intl package very useful as it provides different ways to format numbers.

By default the NumberFormat class format's number in million's using default American locale and we can format numbers in lakh using Indian locale(It can format number or currency according to any countries locale).NumberFormat.decimalPattern([String locale]).

import 'package:intl/intl.dart';   

void main() {
  NumberFormat numberFormat = NumberFormat.decimalPattern('hi');
  print(numberFormat.format(16987));
  print(numberFormat.format(13876));
  print(numberFormat.format(456786));
}

Output

16,987
13,876
4,56,786

You don`t need to use NumberFormat package before you can do that. this should help, test it with any number.

String formatAmount(){
    String price = "1000000000";
    String priceInText = "";
    int counter = 0;
    for(int i = (price.length - 1);  i >= 0; i--){
        counter++;
        String str = price[i];
        if((counter % 3) != 0 && i !=0){
          priceInText = "$str$priceInText";
        }else if(i == 0 ){
          priceInText = "$str$priceInText";
        
        }else{
          priceInText = ",$str$priceInText";
        }
    }
    return priceInText.trim();
  }

Then you can use by printing:

print(formatAmount());

output:

 1,000,000,000

In case you want to format a number with the thousands separator and give it a max number of decimal numbers.

var formatter = NumberFormat('#,##0.' + "#" * 5); 

print(formatter.format(double.parse('1000.456781234'.replaceAll(",", ""))));

OUTPUT: 1,000.45678

Hope this helps. :)

You can use this more flexible extension:

/// Return as number as formatted in thousands string.
/// Example: -123456.asThousands() returns -123'456
String asThousands({
  final String separator = "'",
  final int digits = 3,
}) {
  assert(digits >= 1, '5d40ef0f-f8b4-4070-adf4-bbfc1a8b663b');
  final chars =
      abs().truncate().toString().split(StringHelper.empty).reversed;
  var n = 0;
  var result = StringHelper.empty;
  for (final ch in chars) {
    if (n == digits) {
      result = '$ch$separator$result';
      n = 1;
    } else {
      result = '$ch$result';
      n++;
    }
  }
  result = this < 0 ? '-$result' : result;
  result = (this is double)
      ? '$result${toString().substring(toString().lastIndexOf('.'))}'
      : result;
  return result;
}

Sample calls:

test('Test NumHelper.asThousands()', () {
  expect(
    123456789.asThousands(separator: StringHelper.space),
    '123 456 789',
  );
  expect(123456789.asThousands(separator: ','), '123,456,789');
  expect(
    123456789.asThousands(separator: ',', digits: 2),
    '1,23,45,67,89',
  );
  expect((-123456789).asThousands(separator: ','), '-123,456,789');
  expect((-123456).asThousands(separator: ','), '-123,456');
  expect((-12345).asThousands(separator: ','), '-12,345');
  expect(1.asThousands(), '1');
  expect(12.asThousands(), '12');
  expect(123.asThousands(), '123');
  expect(1995.asThousands(), "1'995");
  expect(12345678.asThousands(), "12'345'678");
  expect((-123456789.123).asThousands(separator: ','), '-123,456,789.123');
});

Pseudocode for that activity would be around:

Here, `string` is an input string with indexes starting at 0.
let i = (length of string) - 3
while i > 0 do
    insert a "," into string at position (i)
    let i = i - 3
return string

DartCode

extension on int {
  String get priceString {
    final numberString = toString();
    final numberDigits = List.from(numberString.split(''));
    int index = numberDigits.length - 3;
    while (index > 0) {
      numberDigits.insert(index, ',');
      index -= 3;
    }
    return numberDigits.join();
  }
}