Question

I’m very unfamiliar with Regular Expressions and I need a way to identify a subset of a matched string.

I asked a question previously about how to parse a string to extract date range values. One of the answers I received was very useful and pretty much gave me everything I needed to solve the problem at hand.

Part of the answer was this regular expression:

string pattern = @"\b(?<Year1>\d{4})(-(?<Year2>\d{2,4}))?\b";

This pattern allows me to identify the first and second year substrings in the string I’m comparing, with <Year1> and <Year2>, and in code all i need to do is:

searchTermMatch.Groups["Year1"].Value

However, I now need to identify the first part of the string. So if the string is

ThingOne ThingTwo 2006-2007 S12 RP

I need to be able to isolate “ThingOne ThingTwo” (which are only alphabetical characters – no numbers) the same as I can for “2006” & “2007”.

I’ve tried changing the pattern to

string pattern = @"\b(<FirstPart>?<Year1>\d{4})(-(?<Year2>\d{2,4}))?\b";

but that didn’t work.. so I’m looking to see if somebody could point out how I can achieve the result I need? Thanks.

Answer 1

@"^(?<FirstPart>.+?)(?<Year1>\d{4})(-(?<Year2>\d{2,4}))?\b"

The syntax works because matches in Regexps are noted by brackets. The naming syntax (which is BTW not supported in all languages) is (?<name_of_match>pattern). So here we get three named matches:

• FirstPart will match .+? = any character repeated more then once but not more times then necessary
• Year1 will match \d{4} = any digit character four times
• Year2 will match \d{2,4} = any digit repeated from two to four times

Also notice the added ^ character at the beginning – it means start at the beginning of the line.