Question

I’ve been playing around with retrieving data from a string using regular expression, mostly as an exercise for myself. The pattern that I’m trying to match looks like this:

"(SomeWord,OtherWord)"

After reading some documentation and looking at a cheat sheet I came to the conclusion that the following regex should give me 2 matches:

"\((\w),(\w)\)"

Because according to the documentation the parenthesis should do the following:

(pattern) Matches pattern and remembers the match. The matched
substring can be retrieved from the resulting Matches collection,
using Item [0]…[n]. To match parentheses characters ( ), use “\ (” or
“\ )”.

However using the following code (removed error checking for conciseness) matches quite something different:

string line = "(A,B)";
string pattern = @"\((\w),(\w)\)";
MatchCollection matches = Regex.Matches(line, pattern);
string left = matches[0].Value;
string right = matches[1].Value;

Now I would expect left to become “A” and right to become “B”. However left becomes “(A,B)” and there is no second match at all. What am I missing here?

(I know this example is trivial to solve without regexes but to learn how to properly use regexes I should be able to make something simple as this work)

Answer 1

You want the Groups member of the first match. In your example case there is only 1 match, which is the whole string. In the Groups collection you will have 3 items. Try this sample code, left should be A, and right should be B. If you look at the group[0] value it will be the whole string.

string line = "(A,B)";
string pattern = @"\((\w),(\w)\)";
MatchCollection matches = Regex.Matches(line, pattern);
GroupCollection groups = matches[0].Groups;
string left = groups[1].Value;
string right = groups[2].Value;