Develop Reference

How to write a regular expression that captures tags in a comma-separated list?

Here is my input:
#
tag1, tag with space, !##%^, 🦄
I would like to match it with a regex and yield the following elements easily:
tag1
tag with space
!##%^
🦄
I know I could do it this way:
var match = Regex.Match(input, #"^#[\n](?<tags>[\S ]+)$");
// if match is a success
var tags = match.Groups["tags"].Value.Split(',').Select(x => x.Trim());
But that's cheating, as it involves messing around with C#. There must be a neat way to do this with a regex. Just must be... right? ;D
The question is: how to write a regular expression that would allow me to iterate through captures and extract tags, without the need of splitting and trimming?

This works (?ms)^\#\s+(?:\s*((?:(?!,|^\#\s+).)*?)\s*(?:,|$))+
It uses C#'s Capture Collection to find a variable amount of field data
in a single record.
You could extend the regex further to get all records at once.
Where each record contains its own variable amount of field data.
The regex has built-in trimming as well.
Expanded:
(?ms) # Inline modifiers: multi-line, dot-all
^ \# \s+ # Beginning of record
(?: # Quantified group, 1 or more times, get all fields of record at once
\s* # Trim leading wsp
( # (1 start), # Capture collector for variable fields
(?: # One char at a time, but not comma or begin of record
(?!
,
| ^ \# \s+
)
.
)*?
) # (1 end)
\s*
(?: , | $ ) # End of this field, comma or EOL
)+
C# code:
string sOL = #"
#
tag1, tag with space, !##%^, 🦄";
Regex RxOL = new Regex(#"(?ms)^\#\s+(?:\s*((?:(?!,|^\#\s+).)*?)\s*(?:,|$))+");
Match _mOL = RxOL.Match(sOL);
while (_mOL.Success)
{
CaptureCollection ccOL1 = _mOL.Groups[1].Captures;
Console.WriteLine("-------------------------");
for (int i = 0; i < ccOL1.Count; i++)
Console.WriteLine(" '{0}'", ccOL1[i].Value );
_mOL = _mOL.NextMatch();
}
Output:
-------------------------
'tag1'
'tag with space'
'!##%^'
'??'
''
Press any key to continue . . .

Nothing wrong with cheating ;]
string input = #"#
tag1, tag with space, !##%^, 🦄";
string[] tags = Array.ConvertAll(input.Split('\n').Last().Split(','), s => s.Trim());

You can pretty much make it without regex. Just split it like this:
var result = input.Split(new []{'\n','\r'}, StringSplitOptions.RemoveEmptyEntries).Skip(1).SelectMany(x=> x.Split(new []{','},StringSplitOptions.RemoveEmptyEntries).Select(y=> y.Trim()));

Regex with balancing groups

I need to write regex that capture generic arguments (that also can be generic) of type name in special notation like this:
System.Action[Int32,Dictionary[Int32,Int32],Int32]
lets assume type name is [\w.]+ and parameter is [\w.,\[\]]+
so I need to grab only Int32, Dictionary[Int32,Int32] and Int32
Basically I need to take something if balancing group stack is empty, but I don't really understand how.
UPD
The answer below helped me solve the problem fast (but without proper validation and with depth limitation = 1), but I've managed to do it with group balancing:
^[\w.]+ #Type name
\[(?<delim>) #Opening bracet and first delimiter
[\w.]+ #Minimal content
(
[\w.]+
((?(open)|(?<param-delim>)),(?(open)|(?<delim>)))* #Cutting param if balanced before comma and placing delimiter
((?<open>\[))* #Counting [
((?<-open>\]))* #Counting ]
)*
(?(open)|(?<param-delim>))\] #Cutting last param if balanced
(?(open)(?!) #Checking balance
)$
Demo
UPD2 (Last optimization)
^[\w.]+
\[(?<delim>)
[\w.]+
(?:
(?:(?(open)|(?<param-delim>)),(?(open)|(?<delim>))[\w.]+)?
(?:(?<open>\[)[\w.]+)?
(?:(?<-open>\]))*
)*
(?(open)|(?<param-delim>))\]
(?(open)(?!)
)$

I suggest capturing those values using
\w+(?:\.\w+)*\[(?:,?(?<res>\w+(?:\[[^][]*])?))*
See the regex demo.
Details:
\w+(?:\.\w+)* - match 1+ word chars followed with . + 1+ word chars 1 or more times
\[ - a literal [
(?:,?(?<res>\w+(?:\[[^][]*])?))* - 0 or more sequences of:
,? - an optional comma
(?<res>\w+(?:\[[^][]*])?) - Group "res" capturing:
\w+ - one or more word chars (perhaps, you would like [\w.]+)
(?:\[[^][]*])? - 1 or 0 (change ? to * to match 1 or more) sequences of a [, 0+ chars other than [ and ], and a closing ].
A C# demo below:
var line = "System.Action[Int32,Dictionary[Int32,Int32],Int32]";
var pattern = #"\w+(?:\.\w+)*\[(?:,?(?<res>\w+(?:\[[^][]*])?))*";
var result = Regex.Matches(line, pattern)
.Cast<Match>()
.SelectMany(x => x.Groups["res"].Captures.Cast<Capture>()
.Select(t => t.Value))
.ToList();
foreach (var s in result) // DEMO
Console.WriteLine(s);
UPDATE: To account for unknown depth [...] substrings, use
\w+(?:\.\w+)*\[(?:\s*,?\s*(?<res>\w+(?:\[(?>[^][]+|(?<o>\[)|(?<-o>]))*(?(o)(?!))])?))*
See the regex demo

Regex replace between and including tags

I have the following line of text (META Title):
Buy [ProductName][Text] at a great price [/Text] from [ShopName] today.
I am replacing depending on what values I have.
I have it working as I require however I can't find the correct regex to replace:
[Text] at a great price [/Text]
The words (in a nd between square brackets) change so the only thing that will remain the same is:
[][/]
i.e I may also want to replace
[TestText]some test text[/TestText] with nothing.
I have this working:
System.Text.RegularExpressions.Regex.Replace(SEOContent, #"\[Text].*?\[/Text]", #"");
I presumed the regex of:
[.*?].*?\[/.*?]
Would work but it didn't! - I'm coding in ASP.NET C#
Thanks in advance,
Dave

Use a named capture to get the node name of [..], then find it again using \k<..>.
(\[(?<Tag>[^\]]+)\][^\[]+\[/\k<Tag>\])
Broken down using Ignore Pattern Whitespace and an example program.
string pattern = #"
( # Begin our Match
\[ # Look for the [ escape anchor
(?<Tag>[^\]]+) # Place anything that is not antother ] into the named match Tag
\] # Anchor of ]
[^\[]+ # Get all the text to the next anchor
\[/ # Anchor of the closing [...] tag
\k<Tag> # Use the named capture subgroup Tag to balance it out
\] # Properly closed end tag/node.
) # Match is done";
string text = "[TestText]some test text[/TestText] with nothing.";
Console.WriteLine (Regex.Replace(text, pattern, "Jabberwocky", RegexOptions.IgnorePatternWhitespace));
// Outputs
// Jabberwocky with nothing.
As an aside, I would actually create a tokenizing regex (using a regex If with the above pattern) and replace within matches by identify the sections by named captures. Then in the replace using a match evaluator replace the identified tokens such as:
string pattern = #"
(?(\[(?<Tag>[^\]]+)\][^\[]+\[/\k<Tag>\]) # If statement to check []..[/] situation
( # Yes it is, match into named captures
\[
(?<Token>[^\]]+) # What is the text inside the [ ], into Token
\]
(?<TextOptional>[^\[]+) # Optional text to reuse
\[
(?<Closing>/[^\]]+) # The closing tag info
\]
)
| # Else, let is start a new check for either [] or plain text
(?(\[) # If a [ is found it is a token.
( # Yes process token
\[
(?<Token>[^\]]+) # What is the text inside the [ ], into Token
\]
)
| # Or (No of the second if) it is just plain text
(?<Text>[^\[]+) # Put it into the text match capture.
)
)
";
string text = #"Buy [ProductName] [Text]at a great price[/Text] from [ShopName] today.";
Console.WriteLine (
Regex.Replace(text,
pattern,
new MatchEvaluator((mtch) =>
{
if (mtch.Groups["Text"].Success) // If just text, return it.
return mtch.Groups["Text"].Value;
if (mtch.Groups["Closing"].Success) // If a Closing match capture group reports success, then process
{
return string.Format("Reduced Beyond Comparison (Used to be {0})", mtch.Groups["TextOptional"].Value);
}
// Otherwise its just a plain old token, swap it out.
switch ( mtch.Groups["Token"].Value )
{
case "ProductName" : return "Jabberwocky"; break;
case "ShopName" : return "StackOverFlowiZon"; break;
}
return "???"; // If we get to here...we have failed...need to determine why.
}),
RegexOptions.IgnorePatternWhitespace | RegexOptions.ExplicitCapture));
// Outputs:
// Buy Jabberwocky Reduced Beyond Comparison (Used to be at a great price) from StackOverFlowiZon today.

Captures count is always zero

I've got a problem. I use following regular expression:
Pattern =
(?'name'\w+(?:\w|\s)*), \s*
(?'category'\w+(?:\w|\s)*), \s*
(?:
\{ \s*
[yY]: (?'year'\d+), \s*
[vV]: (?'volume'(?:([1-9][0-9]*\.?[0-9]*)|(\.[0-9]+))+), \s*
\} \s*
,? \s*
)*
with IgnorePatternWhitespaces option.
Everything seemed fine in my application until I debugged it & encountered a problem.
var Year = default(UInt32);
// ...
if((Match = Regex.Match(Line, Pattern, Options)).Success)
{
// Getting Product header information
Name = Match.Groups["name"].Value;
// Gathering Product statistics
for(var ix = default(Int32); ix < Match.Groups["year"].Captures.Count; ix++)
{
// never get here
Year = UInt32.Parse(Match.Groups["year"].Captures[ix].Value, NumberType, Culture);
}
}
So in the code above.. In my case Match is always successful. I get proper value for Name but when turn comes to for loop program flow just passes it by. I debugged there's no Captures in Match.Groups["year"]. So it is logical behavior. But not obvious to me where I'm wrong. Help!!
There is a previous connected post Extract number values enclosed inside curly brackets I made.
Thanks!
EDIT. Input Samples
Sherwood, reciever, {y:2008,V:5528.35}, {y:2009,V:8653.89}, {y:2010, V:4290.51}
I need to capture 2008, 5528.35, 2009, 8653.89, 2010, 4290.51 values and operate with them as named groups.
2D EDIT
I tried using ExplicitCapture Option and following expression:
(?<name>\w+(w\| )*), (?<category>\w+(w\| )*), (\{[yY]:(?<year>\d+), *[vV]:(?<volume>(([1-9][0-9]*\.?[0-9]*)|(\.[0-9]+))+)\}(, )?)+
But that didn't help.

Edit: You could simplify by matching everything until the next comma: [^,]*. Here's a full code snippet to match your source data:
var testRegex = new Regex(#"
(?'name'[^,]*),\s*
(?'category'[^,]*),\s*
({y:(?'year'[^,]*),\s*
V:(?'volume'[^,]*),?\s*)*",
RegexOptions.IgnorePatternWhitespace);
var testMatches = testRegex.Matches(
"Sherwood, reciev, {y:2008,V:5528.35}, {y:2009,V:8653.89}, {y:2010, V:4290.51}");
foreach (Match testMatch in testMatches)
{
Console.WriteLine("Name = {0}", testMatch.Groups["name"].Value);
foreach (var capture in testMatch.Groups["year"].Captures)
Console.WriteLine(" Year = {0}", capture);
}
This prints:
Name = Sherwood
Year = 2008
Year = 2009
Year = 2010

I think the problem is a comma:
, \s* \}
which should be optional (or omitted?):
,? \s* \}

To expound on what MRAB said:
(?'name'
\w+
(?:
\w|\s
)*
),
\s*
(?'category'
\w+
(?:
\w|\s
)*
),
\s*
(?:
\{
\s*
[yY]:
(?'year'
\d+
),
\s*
[vV]:
(?'volume'
(?:
( # Why do you need capturing parenth's here ?
[1-9][0-9]*
\.?
[0-9]*
)
|
(
\.[0-9]+
)
)+
), # I'm just guessing this comma doesent match input samples
\s*
\}
\s*
,?
\s*
)*
Sherwood, reciever, {y:2008,V:5528.35}, {y:2009,V:8653.89}, {y:2010, V:4290.51}

Need help with regex to parse expression

I have an expression:
((((the&if)|sky)|where)&(end|finish))
What I need is to put a space between symbols and words so that it ends up like:
( ( ( ( the & if ) | sky ) | where ) & ( end | finish ) )
The regex I came up with is (\w)*[(\&*)(\|*)] which only gets me:
( ( ( ( the& if) | sky) | where) & ( end| finish) )
Could I get a little help here from a resident regex guru please? I will be using this in C#.

Edit: Since you're using C#, try this:
output = Regex.Replace(input, #"([^\w\s]|\w(?!\w))(?!$)", "$1 ");
That inserts a space after any character that matches the following conditions:
Is neither a letter, number, underscore, or whitespace
OR is a word character that is NOT followed by another word character
AND is not at the end of a line.

resultString = Regex.Replace(subjectString, #"\b|(?<=\W)(?=\W)", " ");
Explanation:
\b # Match a position at the start or end of a word
| # or...
(?<=\W) # a position between two
(?=\W) # non-word characters
(and replace those with a space).

You could just add a space after each word and after each non-word character (so look for \W|\w+ and replace it with the match and a space. e.g. in Vim:
:s/\W\|\w\+/\0 /g

You could use:
(\w+|&|\(|\)|\|)(?!$)
which means a word, or a & symbol, or a ( symbol, or a ) symbol, or a | symbol not followed by an end of string; and then replace a match with a match + space symbol. By using c# this could be done like:
var result = Regex.Replace(
#"((((the&if)|sky)|where)&(end|finish))",
#"(\w+|&|\(|\)|\|)(?!$)",
"$+ "
);
Now result variable contains a value:
( ( ( ( the & if ) | sky ) | where ) & ( end | finish ) )