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Regular Expression for Digits and Special Characters - C#

I use Html-Agility-Pack to extract information from some websites. In the process I get data in the form of string and I use that data in my program.
Sometimes the data I get includes multiple details in the single string. As the name of this Movie "Dog Eats Dog (2012) (2012)". The name should have been "Dog Eats Dog (2012)" rather than the first one.
Above is the one example from many. In order to correct the issue I tried to use string.Distinct() method but it would remove all the duplicate characters in the string as in above example it would return "Dog Eats (2012)". Now it solved my initial problem by removing the 2nd (2012) but created a new one by changing the actual title.
I thought my problem could be solved with Regex but I have no idea as to how I can use it here. As far as I know if I use Regex it would tell me that there are duplicate items in the string according to the defined Regex code.
But how do I remove it? There can be a string like "Meme 2013 (2013) (2013)".
Now the actual title is "Meme 2013" with year (2013) and the duplicate year (2013). Even if I get a bool value indicating that the string has duplicate year, I cant think of any method to actually remove the duplicate substring.
The duplicate year always comes in the end of the string. So what should be the Regex that I would use to determine that the string actually has two years in it, like (2012) (2012)?
If I can correctly identify the string contains duplicate maybe I can use string.LastIndexOf() to try and remove the duplicate part. If there is any better way to do it please let me know.
Thanks.

The right regex is "( \(\d{4}\))\1+".
string pattern = #"( \(\d{4}\))\1+";
new Regex(pattern).Replace(s, "$1");
Example here : https://repl.it/Evcy/2
Explanation:
Capture one " (dddd)" block, and remove all following identical ones.
( \(\d{4}\)) does the capture, \1+ finds any non empty sequence of that captured block
Finally, replace the initial block and its copies by the initial block alone.

This regex will allow for any pattern of whitespace, even none, as in (2013)(2013)
`#"(\(\d{4}\))(?:\s*\1)+"`
I have a demo of it here

Replace every occurrence of a Regex match EXCEPT for the first?

I don't have my code with me at home but I realized that I'll need to do a regex replace on a certain expression and I was wondering if there is a best practices for this.
What my code is currently doing is searching for matches in files, taking those matches out of a file(replacing them with ""), and then once all the files are processed I make a call to the .NET Process class to do some command line stuff. Specifically what i'll be doing is taking a group of files and copying them(merging)into one final output file. But there is the instance where every file to be merged has the exact same first line, which let's just say for the example is:
FIRST_NAME|MIDDLE_NAME|LAST_NAME|ADDRESS
Now, the first file having that is okay. And I figure that I'm going to do this final match and replace once the file is merged. But I only want to replace matches of that specific expression AFTER the first occurrence.
So, I read that C# has superb support for a Regex look behind? Would that be the proper way to implement "replacing matches after the first occurrence of a match" and if so how would you implement it given a sample regular expression?
My own personal solution to this was to return the amount of files in the folder with Directory.GetFiles and then in my foreach (string file in matches) I would declare a quick condition that says
if (count == directoryCount)
do not match and replace
count minus 1
elseif (count < directoryCount)
strip matching expression
and then every iteration through the foreach after the first run-through will strip out the matching expression from the file leaving only the first file with the expression I want to keep.
Thank you for any suggestions.

how about using replaceFirst() to backup the first occurency and mark it with some char. then use replaceAll(), and replaceFirst() again to roll back the first match.

Regex.Replace has a couple of overloads that provide for MatchEvaluator evaluator which is delegate on a Match returning the replacement String.
So you can use something like re.Replace(input, m => first ? (first=false, m.Value) : "") (but I've a VB programmer and have put this in without any syntax checking).

Regular Expression to match a quoted string embedded in another quoted string

I have a data source that is comma-delimited, and quote-qualified. A CSV. However, the data source provider sometimes does some wonky things. I've compensated for all but one of them (we read in the file line-by-line, then write it back out after cleansing), and I'm looking to solve the last remaining problem when my regex-fu is pretty weak.
Matching a Quoted String inside of another Quoted String
So here is our example string...
"foobar", 356, "Lieu-dit "chez Métral", Chilly, FR", "-1,000.09", 467, "barfoo", 1,345,456,235,231, "935.18"
I am looking to match the substring "chez Métral", in order to replace it with the substring chez Métral. Ideally, in as few lines of code as possible. The final goal is to write the line back out (or return it as a method return value) with the replacement already done.
So our example string would end up as...
"foobar", 356, "Lieu-dit chez Métral, Chilly, FR", "-1,000.09", 467, "barfoo", 1,345,456,235,231, "935.18"
I know I could define a pattern such as (?<quotedstring>\"\w+[^,]+\") to match quoted strings, but my regex-fu is weak (database developer, almost never use C#), so I'm not sure how to match another quoted string within the named group quotedstring.
FYI: For those noticing the large integer that is formatted with commas but not quote-qualified, that's already handled. As is the random use of row-delimiters (sometimes CR, sometimes LF). As other problems...

Replace with this regex
(?<!,\s*|^)"([^",]*)"
now replace it with $1
try it here
escaping " with "" it would become
(?<!,\s*|^)""([^"",]*)""

Regex between, from the last to specific end

Today my wish is to take text form the string.
This string must be, between last slash and .partX.rar or .rar
First I tried to find edge's end of the word and then the beginning. After I get that two elements I merged them but I got empty results.
String:
http://hosting.xyz/1234/15-game.part4.rar.html
http://hosting.xyz/1234/16-game.rar.html
Regex:
Begin:(([^/]*)$) - start from last /
End:(.*(?=.part[0-9]+.rar|.rar)) stop before .partX.rar or .rar
As you see, if I merge that codes I won't get any result.
What is more, "end" select me only .partX instead of .partX.rar
All what I want is:
15-game.part4.rar and 16-game.rar
What i tried:
(([^/]*)$)(.*(?=.part[0-9]+.rar|.rar))
(([^/]*)$)
(.*(?=.part[0-9]+.rar|.rar))
I tried also
/[a-zA-Z0-9]+
but I do not know how select symbols.. This could be the easiest way. But this select only letters and numbers, not - or _.
If I could select symbols..

You don't really need a regex for this as you can merely split the url on / and then grab the part of the file name that you need. Since you didn't mention a language, here's an implementation in Perl:
use strict;
use warnings;
my $str1="http://hosting.xyz/1234/15-game.part4.rar.html";
my $str2="http://hosting.xyz/1234/16-game.rar.html";
my $file1=(split(/\//,$str1))[-1]; #last element of the resulting array from splitting on slash
my $file2=(split(/\//,$str2))[-1];
foreach($file1,$file2)
{
s/\.html$//; #for each file name, if it ends in ".html", get rid of that ending.
print "$_\n";
}
The output is:
15-game.part4.rar
16-game.rar

Nothing could be simpler! :-)
Use this:
new Regex("^.*\/(.*)\.html$")
You'll find your filename in the first captured group (don't have a c# compiler at hand, so can't give you working sample, but you have a working regex now! :-) )
See a demo here: http://rubular.com/r/UxFNtJenyF

I'm not a C# coder so can't write full code here but I think you'll need support of negative lookahead here like this:
new Regex("/(?!.*/)(.+?)\.html$");
Matched Group # 1 will have your string i.e. "16-game.rar" OR "15-game.part4.rar"

Use two regexes:
start to substitute .*/ with nothing;
then substitute \.html with nothing.
Job done!

Parsing a CSV File with C#, ignoring thousand separators

Working on a program that takes a CSV file and splits on each ",". The issue I have is there are thousand separators in some of the numbers. In the CSV file, the numbers render correctly. When viewed as a text document, they are shown like below:
Dog,Cat,100,100,Fish
In a CSV file, there are four cells, with the values "Dog", "Cat", "100,000", "Fish". When I split on the "," to an array of strings, it contains 5 elements, when what I want is 4. Anyone know a way to work around this?
Thanks

There are two common mistakes made when reading csv code: using a split() function and using regular expressions. Both approaches are wrong, in that they are prone to corner cases such as yours and slower than they could be.
Instead, use a dedicated parser such as Microsoft.VisualBasic.TextFieldParser, CodeProject's FastCSV or Linq2csv, or my own implemention here on Stack Overflow.

Typically, CSV files would wrap these elements in quotes, causing your line to be displayed as:
Dog,Cat,"100,100",Fish
This would parse correctly (if using a reasonable method, ie: the TextFieldParser class or a 3rd party library), and avoid this issue.
I would consider your file as an error case - and would try to correct the issue on the generation side.
That being said, if that is not possible, you will need to have more information about the data structure in the file to correct this. For example, in this case, you know you should have 4 elements - if you find five, you may need to merge back together the 3rd and 4th, since those two represent the only number within the line.
This is not possible in a general case, however - for example, take the following:
100,100,100
If that is 2 numbers, should it be 100100, 100, or should it be 100, 100100? There is no way to determine this without more information.

you might want to have a look at the free opensource project FileHelpers. If you MUST use your own code, here is a primer on the CSV "standard" format

well you could always split on ("\",\"") and then trim the first and last element.
But I would look into regular expressions that match elements with in "".

Don't just split on the , split on ", ".
Better still, use a CSV library from google or codeplex etc
Reading a CSV file in .NET?

You may be able to use Regex.Replace to get rid of specifically the third comma as per below before parsing?
Replaces up to a specified number of occurrences of a pattern specified in the Regex constructor with a replacement string, starting at a specified character position in the input string. A MatchEvaluator delegate is called at each match to evaluate the replacement.
[C#] public string Replace(string, MatchEvaluator, int, int);

I ran into a similar issue with fields with line feeds in. Im not convinced this is elegant, but... For mine I basically chopped mine into lines, then if the line didnt start with a text delimeter, I appended it to the line above.
You could try something like this : Step through each field, if the field has an end text delimeter, move to the next, if not, grab the next field, appaend it, rince and repeat till you do have an end delimeter (allows for 1,000,000,000 etc) ..
(Im caffeine deprived, and hungry, I did write some code but it was so ugly, I didnt even post it)

Do you know that it will always contain exactly four columns? If so, this quick-and-dirty LINQ code would work:
string[] elements = line.Split(',');
string element1 = elements.ElementAt(0);
string element2 = elements.ElementAt(1);
// Exclude the first two elements and the last element.
var element3parts = elements.Skip(2).Take(elements.Count() - 3);
int element3 = Convert.ToInt32(string.Join("",element3parts));
string element4 = elements.Last();
Not elegant, but it works.