Removing commas from formula using regex

Question

I'm trying to format numbers in Javascript using regex where the numbers are part of a formula. For example, given 12345.6789+9876.54321*-100 the result should be 12,345.6789+9,876.54321*-100.

This is my attempt:

str.replace(/(\d)(?=(\d\d\d)+(?!\d))/g, "$1,")

and the result:

12345.6,789+9876.54,321*-100

It inserts commas in decimal places (PLUNK), how to fix this?

@JaromandaX the problem wasn't commas appearing, it was that they appear after `.` indicating decimals, which is not desired behaviour. — Julian Zucker, Sep 13 '17 at 01:45
nevermind, I did re-read the problem :p I wish people would show what the result IS as well !!! — Jaromanda X, Sep 13 '17 at 01:45
If you don't have to use regex, [this](https://stackoverflow.com/questions/149055/how-can-i-format-numbers-as-dollars-currency-string-in-javascript) is what you're looking for — Julian Zucker, Sep 13 '17 at 01:49
My feeling is that you might need a parser to handle this. Extract each number term, then do a replacement to bring in the commas. — Tim Biegeleisen, Sep 13 '17 at 01:54
If the integer part of each number is less than 6 digits, how about this? ``var res = str.replace(/(\d\d\d)\./g, ",$1.")`` If this was not useful for you, I'm sorry. — Tanaike, Sep 13 '17 at 02:02
you can modify your pattern to `/((?:^|[^\d\.])(?:\d+))(?=(\d\d\d)+(?!\d))/g` and that will ignore numbers after point but pattern works with integers < 1M only. — Wh1T3h4Ck5, Sep 13 '17 at 02:12
@Wh1T3h4Ck5 thanks, but it needs to work with integers > 1M as well — ps0604, Sep 13 '17 at 02:16

skirtle · Accepted Answer · 2017-09-13T02:37:00.327

My current feeling is that this isn't possible with a single RegExp but I'm still hopeful someone will find a way. I suspect it would need support for lookbehind.

My best attempt so far requires a nested replace so it's definitely cheating:

// Test cases
[
    '1',
    '12',
    '123',
    '1234',
    '12345',
    '123456',
    '1234567',
    '12345678',
    '123456789',
    '1234567890',
    
    '1.23',
    '1.234',
    '1.2345',
    '1.234567890',
    
    '1234567890.1234567890',
    
    '1+2-3+4',
    '12+34-56+78',
    '123+456-789',
    
    '1234+5678',
    '12345-678',
    '1234567-8',
    
    '-123456.7890',
    '1+2-3456.7890',
    '1+2-3456.7890+123456789-0.1234'
    
].forEach(function(str) {
    var out = str.replace(/(?:^|[^\.\d])\d+/g, function(match) {
        return match.replace(/(\d)(?=(\d\d\d)+$)/g, '$1,');
    });
    
    console.log(out);
});

The outer RegExp grabs the integer part of each number (and possibly the character before it too but that doesn't hurt) and the inner replace inserts the commas in a similar fashion to the OP.

Wh1T3h4Ck5 · Answer 2 · 2017-09-13T03:31:31.253

Unfortunately, JavaScript doesn't support lookbehind syntax (?<=) so you must do some basic parsing to handle this task. One of dozens of easy solutions could be:

  var formatNum = function(s) {
    var r = "", m = s.match(/(?:^|\+|-|\*-?|\/|\.)(\d+)/g);
    for (var i=0; i<m.length; i++)
        r += m[i][0] != "." 
               ? m[i].replace(/\B(?=(\d{3})+(?!\d))/g, ",") 
               : m[i];
    return r
  };


  // test
  console.log (formatNum("12345.6789+9876.54321*-100"));
  console.log (formatNum("1000000000000.123456*-74300.0039/438372323.12312312"));

This way you can use extremely large numbers and get comma-separated thousands in integer part only.

Removing commas from formula using regex

2 Answers2