Optional group in Regex returns too many matches

Question

I want to match only values (ie 2.699.230,20) from an input on a C# Regex class.

I use "(\\\\.?[0-9]){2,}\\\\,[0-9]{2}" and it matches desired values 5.000,00 , 2.699.230,20 , 1.000.000,00 , etc. The {2,} is to only match values above 999,99 .

But there's also other values on the same input that i want to match. They are always 1.000 or above, but the difference is that it don't have the decimal ,00 part. Examples: 4.541.087 , 8.997.434 .

So i put the last part of the regex a binary (0 or 1 times present) option (added (...)? around the decimal part:

"(\\\\.?[0-9]){2,}(\\\\,[0-9]{2})?" , but now this matches hundreds of numbers, including 18 , 1.0 , 1.5.2 , 8854 , etc.

So, how can i make the decimal part optional, so it matches both 1.000,00 and 1.000 ?

Answer 1

It seems you only want to get numbers that have a . as thousand separator in them with optional 2 digits in the fractional part.

Use

@"\b\d{1,3}(?:\.\d{3})+(?:,\d{2})?\b"

See the regex demo .

Details :

• \\b - leading word boundary (may be replaced with (?<!\\d) negative lookbehind to disallow only digit before...)
• \\d{1,3} - 1 to 3 digits
• (?:\\.\\d{3})+ - 1 or more sequences of a dot and 3 digits ( NOTE : if you change + with * , it will match values below 1.000 )
• (?:,\\d{2})? - an optional sequence of a , and 2 digits.
• \\b - trailing word boundary (may be replaced with (?!\\d) negative lookbahead to disallow only digit after the number).

C# demo :

var re = @"\b\d{1,3}(?:\.\d{3})+(?:,\d{2})?\b"; 
var str = "values 5.000,00, 2.699.230,20, 1.000.000,00, etc.  999,99 including 18, 1.0, 1.5.2, 8854, etc"; 
var res = Regex.Matches(str, re)
    .Cast<Match>()
    .Select(p => p.Value)
    .ToList();
Console.WriteLine(string.Join("\n", res));