I am trying to use Regex.SPlit to split a a string in order to keep all of its contents, including the delimiters i use. The string is a math problem. For example, 5+9/2*1-1. I have it working if the string contains a + sign but I don't know how to add more then one to the delimiter list. I have looked online at multiple pages but everything I try gives me errors. Here is the code for the Regex.Split line I have: (It works for the plus, Now i need it to also do -,*, and /.
string[] everything = Regex.Split(inputBox.Text, #"(\+)");
Use a character class to match any of the math operations: [*/+-]
string input = "5+9/2*1-1";
string pattern = #"([*/+-])";
string[] result = Regex.Split(input, pattern);
Be aware that character classes allow ranges, such as [0-9], which matches any digit from 0 up to 9. Therefore, to avoid accidental ranges, you can escape the - or place it at either the beginning or end of the character class.
Been scratching my head all day about this one!
Ok, so I have a string which contains the following:
?\"width=\"1\"height=\"1\"border=\"0\"style=\"display:none;\">');
I want to convert that string to the following:
?\"width=1height=1border=0style=\"display:none;\">');
I could theoretically just do a String.Replace on "\"1\"" etc. But this isn't really a viable option as the string could theoretically have any number within the expression.
I also thought about removing the string "\"", however there are other occurrences of this which I don't want to be replaced.
I have been attempting to use the Regex.Replace method as I believe this exists to solve problems along my lines. Here's what I've got:
chunkContents = Regex.Replace(chunkContents, "\".\"", ".");
Now that really messes things up (It replaces the correct elements, but with a full stop), but I think you can see what I am attempting to do with it. I am also worrying that this will only work for single numbers (\"1\" rather than \"11\").. So that led me into thinking about using the "*" or "+" expression rather than ".", however I foresaw the problem of this picking up all of the text inbetween the desired characters (which are dotted all over the place) whereas I obviously only want to replace the ones with numeric characters in between them.
Hope I've explained that clearly enough, will be happy to provide any extra info if needed :)
Try this
var str = "?\"width=\"1\"height=\"1234\"border=\"0\"style=\"display:none;\">');";
str = Regex.Replace(str , "\"(\\d+)\"", "$1");
(\\d+) is a capturing group that looks for one or more digits and $1 references what the group captured.
This works
String input = #"?\""width=\""1\""height=\""1\""border=\""0\""style=\""display:none;\"">');";
//replace the entire match of the regex with only what's captured (the number)
String result = Regex.Replace(input, #"\\""(\d+)\\""", match => match.Result("$1"));
//control string for excpected result
String shouldBe = #"?\""width=1height=1border=0style=\""display:none;\"">');";
//prints true
Console.WriteLine(result.Equals(shouldBe).ToString());
I have a search string that is getting passed
Eg: "a+b",a, b, "C","d+e",a-b,d
I want to filter out all sub strings surrounded by double quotes("").
In above sample Output should contain:
"a+b","C","d+e"
Is there a way to do this without looping?
Also I then need to extract a string without above values to do further processing
Eg: a,b,a-b,d
Any suggestions on how to do this with minimal performance impact?
Thank you in advance for all your comments and suggestions
Since you didn't say anything about how exactly you want your output (do you need to keep the commas and extra whitespace? Is it comma delimited to begin with? Let's assume that it is NOT comma delimited and you are just trying to remove the occurences of the "xyz":
string strRegex = #"""([^""])+""";
string strTargetString = #" ""a+b"",a, b, ""C"",""d+e"",a-b,d";
string strOutput = Regex.Replace(strTargetString, strRegex, x => "");
Will remove all of the items (leaving the extra commas and whitespace).
If you are trying to do something where you need each individual match then you might want to try:
var y = (from Match m in Regex.Matches(strTargetString, strRegex) select m.Value).ToList<string>();
y.ForEach(s => Console.WriteLine(s));
To get the list of items without the surrounding quotes, you could either reverse the regex pattern OR use the replace method in the first code sample and then split on the commas, trimming white space (again, assuming you are splitting on commas which it sounds like you are)
First, add a comma to the end of your output:
"a+b",a, b, "C","d+e",a-b,d,
Then, use this regular expression:
((?<quoted>\".+?\")|(?<unquoted>.+?)),\s*
Now you have 2 problems. Kidding!
You'll have to find a way of extracting the matches without using a loop, but at least they are separated into quoted and unquoted strings by using the group. You could use a lamdba expression to pull the data out and join it, one each for quoted and unquoted, but it's just doing a loop behind the scenes, and may add more overhead than a simple for loop. It sounds like you're trying to eek out performance here, so time and test each method to see what gives the best results.
I'm trying to extract information out of rc-files. In these files, "-chars in strings are escaped by doubling them ("") analog to c# verbatim strings. is ther a way to extract the string?
For example, if I have the following string "this is a ""test""" I would like to obtain this is a ""test"". It also must be non-greedy (very important).
I've tried to use the following regular expression;
"(?<text>[^""]*(""(.|""|[^"])*)*)"
However the performance was awful.
I'v based it on the explanation here: http://ad.hominem.org/log/2005/05/quoted_strings.php
Has anybody any idea to cope with this using a regular expression?
You've got some nested repetition quantifiers there. That can be catastrophic for the performance.
Try something like this:
(?<=")(?:[^"]|"")*(?=")
That can now only consume either two quotes at once... or non-quote characters. The lookbehind and lookahead assert, that the actual match is preceded and followed by a quote.
This also gets you around having to capture anything. Your desired result will simply be the full string you want (without the outer quotes).
I do not assert that the outer quotes are not doubled. Because if they were, there would be no way to distinguish them from an empty string anyway.
This turns out to be a lot simpler than you'd expect. A string literal with escaped quotes looks exactly like a bunch of simple string literals run together:
"Some ""escaped"" quotes"
"Some " + "escaped" + " quotes"
So this is all you need to match it:
(?:"[^"]*")+
You'll have to strip off the leading and trailing quotes in a separate step, but that's not a big deal. You would need a separate step anyway, to unescape the escaped quotes (\" or "").
Don't if this is better or worse than m.buettner's (guessing not - he seems to know his stuff) but I thought I'd throw it out there for critique.
"(([^"]+(""[^"]+"")*)*)"
Try this (?<=^")(.*?"{2}.*?"{2})(?="$)
it will be maybe more faster, than two previous
and without any bugs.
Match a " beginning the string
Multiple times match a non-" or two "
Match a " ending the string
"([^"]|(""))*?"
How to remove ,(comma) which is between "(double inverted comma) and "(double inverted comma). Like there is "a","b","c","d,d","e","f" and then from this, between " and " there is one comma which should be removed and after removing that comma it should be "a","b","c","dd","e","f" with the help of the regex in C# ?
EDIT: I forgot to specify that there may be double comma between quotes like "a","b","c","d,d,d","e","f" for it that regex does not work. and there can be any number of comma between quotes.
And there can be string like a,b,c,"d,d",e,f then there should be result like a,b,c,dd,e,f and if string like a,b,c,"d,d,d",e,f then result should be like a,b,c,ddd,e,f.
Assuming the input is as simple as your examples (i.e., not full-fledged CSV data), this should do it:
string input = #"a,b,c,""d,d,d"",e,f,""g,g"",h";
Console.WriteLine(input);
string result = Regex.Replace(input,
#",(?=[^""]*""(?:[^""]*""[^""]*"")*[^""]*$)",
String.Empty);
Console.WriteLine(result);
output: a,b,c,"d,d,d",e,f,"g,g",h
a,b,c,"ddd",e,f,"gg",h
The regex matches any comma that is followed by an odd number of quotation marks.
EDIT: If fields are quoted with apostrophes (') instead of quotation marks ("), the technique is exactly the same--except you don't have to escape the quotes:
string input = #"a,b,c,'d,d,d',e,f,'g,g',h";
Console.WriteLine(input);
string result = Regex.Replace(input,
#",(?=[^']*'(?:[^']*'[^']*')*[^']*$)",
String.Empty);
Console.WriteLine(result);
If some fields were quoted with apostrophes while others were quoted with quotation marks, a different approach would be needed.
EDIT: Probably should have mentioned this in the previous edit, but you can combine those two regexes into one regex that will handle either apostrophes or quotation marks (but not both):
#",(?=[^']*'(?:[^']*'[^']*')*[^']*$|[^""]*""(?:[^""]*""[^""]*"")*[^""]*$)"
Actually, it will handle simple strings like 'a,a',"b,b". The problem is that there would be nothing to stop you from using one of the quote characters in a quoted field of the other type, like '9" Nails' (sic) or "Kelly's Heroes". That's taking us into full-fledged CSV territory (if not beyond), and we've already established that we're not going there. :D
They're called regular expressions for a reason — they are used to process strings that meet a very specific and academic definition for what is "regular". It looks like you have some fairly typical csv data here, and it happens that csv strings are outside of that specific definition: csv data is not formally "regular".
In spite of this, it can be possible to use regular expressions to handle csv data. However, to do so you must either use certain extensions to normal regular expressions to make them Turing complete, know certain constraints about your specific csv data that is not promised in the general case, or both. Either way, the expressions required to do this are unwieldly and difficult to manage. It's often just not a good idea, even when it's possible.
A much better (and usually faster) solution is to use a dedicated CSV parser. There are two good ones hosted at code project (FastCSV and Linq-to-CSV), there is one (actually several) built into the .Net Framework (Microsoft.VisualBasic.TextFieldParser), and I have one here on Stack Overflow. Any of these will perform better and just plain work better than a solution based on regular expressions.
Note here that I'm not arguing it can't be done. Most regular expression engines today have the necessary extensions to make this possible, and most people parsing csv data know enough about the data they're handling to constrain it appropriately. I am arguing that it's slower to execute, harder to implement, harder to maintain, and more error-prone compared to a dedicated parser alternative, which is likely built into whichever platform you're using, and is therefore not in your best interests.
var input = "\"a\",\"b\",\"c\",\"d,d\",\"e\",\"f\"";
var regex = new Regex("(\"\\w+),(\\w+\")");
var output = regex.Replace(input,"$1$2");
Console.WriteLine(output);
You'd need to evaluate whether or not \w is what you want to use.
You can use this:
var result = Regex.Replace(yourString, "([a-z]),", "$1");
Sorry, after seeing your edits, regular expressions are not appropriate for this.
This should be very simple using Regex.Replace and a callback:
string pattern = #"
"" # open quotes
[^""]* # some not quotes
"" # closing quotes
";
data = Regex.Replace(data, pattern, m => m.Value.Replace(",", ""),
RegexOptions.IgnorePatternWhitespace);
You can even make a slight modification to allow escaped quotes (here I have \", and the comments explain how to use "":
string pattern = #"
\\. # escaped character (alternative is be """")
|
(?<Quotes>
"" # open quotes
(?:\\.|[^""])* # some not quotes or escaped characters
# the alternative is (?:""""|[^""])*
"" # closing quotes
)
";
data = Regex.Replace(data, pattern,
m => m.Groups["Quotes"].Success ? m.Value.Replace(",", "") : m.Value,
RegexOptions.IgnorePatternWhitespace);
If you need a single quote replace all "" in the pattern with a single '.
Something like the following, perhaps?
"(,)"