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How remove some special words from a string content?

I have some strings containing code for emoji icons, like :grinning:, :kissing_heart:, or :bouquet:. I'd like to process them to remove the emoji codes.
For example, given:
Hello:grinning: , how are you?:kissing_heart: Are you fine?:bouquet:
I want to get this:
Hello , how are you? Are you fine?
I know I can use this code:
richTextBox2.Text = richTextBox1.Text.Replace(":kissing_heart:", "").Replace(":bouquet:", "").Replace(":grinning:", "").ToString();
However, there are 856 different emoji icons I have to remove (which, using this method, would take 856 calls to Replace()). Is there any other way to accomplish this?

You can use Regex to match the word between :anything:. Using Replace with function you can make other validation.
string pattern = #":(.*?):";
string input = "Hello:grinning: , how are you?:kissing_heart: Are you fine?:bouquet: Are you super fan, for example. :words not to replace:";
string output = Regex.Replace(input, pattern, (m) =>
{
if (m.ToString().Split(' ').Count() > 1) // more than 1 word and other validations that will help preventing parsing the user text
{
return m.ToString();
}
return String.Empty;
}); // "Hello , how are you? Are you fine? Are you super fan, for example. :words not to replace:"
If you don't want to use Replace that make use of a lambda expression, you can use \w, as #yorye-nathan mentioned, to match only words.
string pattern = #":(\w*):";
string input = "Hello:grinning: , how are you?:kissing_heart: Are you fine?:bouquet: Are you super fan, for example. :words not to replace:";
string output = Regex.Replace(input, pattern, String.Empty); // "Hello , how are you? Are you fine? Are you super fan, for example. :words not to replace:"

string Text = "Hello:grinning: , how are you?:kissing_heart: Are you fine?:bouquet:";
i would solve it that way
List<string> Emoj = new List<string>() { ":kissing_heart:", ":bouquet:", ":grinning:" };
Emoj.ForEach(x => Text = Text.Replace(x, string.Empty));
UPDATE - refering to Detail's Comment
Another approach: replace only existing Emojs
List<string> Emoj = new List<string>() { ":kissing_heart:", ":bouquet:", ":grinning:" };
var Matches = Regex.Matches(Text, #":(\w*):").Cast<Match>().Select(x => x.Value);
Emoj.Intersect(Matches).ToList().ForEach(x => Text = Text.Replace(x, string.Empty));
But i'm not sure if it's that big difference for such short chat-strings and it's more important to have code that's easy to read/maintain. OP's question was about reducing redundancy Text.Replace().Text.Replace() and not about the most efficient solution.

I would use a combination of some of the techniques already suggested. Firstly, I'd store the 800+ emoji strings in a database and then load them up at runtime. Use a HashSet to store these in memory, so that we have a O(1) lookup time (very fast). Use Regex to pull out all potential pattern matches from the input and then compare each to our hashed emoji, removing the valid ones and leaving any non-emoji patterns the user has entered themselves...
public class Program
{
//hashset for in memory representation of emoji,
//lookups are O(1), so very fast
private HashSet<string> _emoji = null;
public Program(IEnumerable<string> emojiFromDb)
{
//load emoji from datastore (db/file,etc)
//into memory at startup
_emoji = new HashSet<string>(emojiFromDb);
}
public string RemoveEmoji(string input)
{
//pattern to search for
string pattern = #":(\w*):";
string output = input;
//use regex to find all potential patterns in the input
MatchCollection matches = Regex.Matches(input, pattern);
//only do this if we actually find the
//pattern in the input string...
if (matches.Count > 0)
{
//refine this to a distinct list of unique patterns
IEnumerable<string> distinct =
matches.Cast<Match>().Select(m => m.Value).Distinct();
//then check each one against the hashset, only removing
//registered emoji. This allows non-emoji versions
//of the pattern to survive...
foreach (string match in distinct)
if (_emoji.Contains(match))
output = output.Replace(match, string.Empty);
}
return output;
}
}
public class MainClass
{
static void Main(string[] args)
{
var program = new Program(new string[] { ":grinning:", ":kissing_heart:", ":bouquet:" });
string output = program.RemoveEmoji("Hello:grinning: :imadethis:, how are you?:kissing_heart: Are you fine?:bouquet: This is:a:strange:thing :to type:, but valid :nonetheless:");
Console.WriteLine(output);
}
}
Which results in:
Hello :imadethis:, how are you? Are you fine? This is:a:strange:thing :to type:,
but valid :nonetheless:

You do not have to replace all 856 emoji's. You only have to replace those that appear in the string. So have a look at:
Finding a substring using C# with a twist
Basically you extract all tokens ie the strings between : and : and then replace those with string.Empty()
If you are concerned that the search will return strings that are not emojis such as :some other text: then you could have a hash table lookup to make sure that replacing said found token is appropriate to do.

Finally got around to write something up. I'm combining a couple previously mentioned ideas, with the fact we should only loop over the string once. Based on those requirement, this sound like the perfect job for Linq.
You should probably cache the HashSet. Other than that, this has O(n) performance and only goes over the list once. Would be interesting to benchmark, but this could very well be the most efficient solution.
The approach is pretty straight forwards.
First load all Emoij in a HashSet so we can quickly look them up.
Split the string with input.Split(':') at the :.
Decide if we keep the current element.
If the last element was a match, keep the current element.
If the last element was no match, check if the current element matches.
If it does, ignore it. (This effectively removes the substring from the output).
If it doesn't, append : back and keep it.
Rebuild our string with a StringBuilder.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
static class Program
{
static void Main(string[] args)
{
ISet<string> emojiList = new HashSet<string>(new[] { "kissing_heart", "bouquet", "grinning" });
Console.WriteLine("Hello:grinning: , ho:w: a::re you?:kissing_heart:kissing_heart: Are you fine?:bouquet:".RemoveEmoji(':', emojiList));
Console.ReadLine();
}
public static string RemoveEmoji(this string input, char delimiter, ISet<string> emojiList)
{
StringBuilder sb = new StringBuilder();
input.Split(delimiter).Aggregate(true, (prev, curr) =>
{
if (prev)
{
sb.Append(curr);
return false;
}
if (emojiList.Contains(curr))
{
return true;
}
sb.Append(delimiter);
sb.Append(curr);
return false;
});
return sb.ToString();
}
}
}
Edit: I did something cool using the Rx library, but then realized Aggregate is the IEnumerable counterpart of Scan in Rx, thus simplifying the code even more.

If efficiency is a concern and to avoid processing "false positives", consider rewriting the string using a StringBuilder while skipping the special emoji tokens:
static HashSet<string> emojis = new HashSet<string>()
{
"grinning",
"kissing_heart",
"bouquet"
};
static string RemoveEmojis(string input)
{
StringBuilder sb = new StringBuilder();
int length = input.Length;
int startIndex = 0;
int colonIndex = input.IndexOf(':');
while (colonIndex >= 0 && startIndex < length)
{
//Keep normal text
int substringLength = colonIndex - startIndex;
if (substringLength > 0)
sb.Append(input.Substring(startIndex, substringLength));
//Advance the feed and get the next colon
startIndex = colonIndex + 1;
colonIndex = input.IndexOf(':', startIndex);
if (colonIndex < 0) //No more colons, so no more emojis
{
//Don't forget that first colon we found
sb.Append(':');
//Add the rest of the text
sb.Append(input.Substring(startIndex));
break;
}
else //Possible emoji, let's check
{
string token = input.Substring(startIndex, colonIndex - startIndex);
if (emojis.Contains(token)) //It's a match, so we skip this text
{
//Advance the feed
startIndex = colonIndex + 1;
colonIndex = input.IndexOf(':', startIndex);
}
else //No match, so we keep the normal text
{
//Don't forget the colon
sb.Append(':');
//Instead of doing another substring next loop, let's just use the one we already have
sb.Append(token);
startIndex = colonIndex;
}
}
}
return sb.ToString();
}
static void Main(string[] args)
{
List<string> inputs = new List<string>()
{
"Hello:grinning: , how are you?:kissing_heart: Are you fine?:bouquet:",
"Tricky test:123:grinning:",
"Hello:grinning: :imadethis:, how are you?:kissing_heart: Are you fine?:bouquet: This is:a:strange:thing :to type:, but valid :nonetheless:"
};
foreach (string input in inputs)
{
Console.WriteLine("In <- " + input);
Console.WriteLine("Out -> " + RemoveEmojis(input));
Console.WriteLine();
}
Console.WriteLine("\r\n\r\nPress enter to exit...");
Console.ReadLine();
}
Outputs:
In <- Hello:grinning: , how are you?:kissing_heart: Are you fine?:bouquet:
Out -> Hello , how are you? Are you fine?
In <- Tricky test:123:grinning:
Out -> Tricky test:123
In <- Hello:grinning: :imadethis:, how are you?:kissing_heart: Are you fine?:bouquet: This is:a:strange:thing :to type:, but valid :nonetheless:
Out -> Hello :imadethis:, how are you? Are you fine? This is:a:strange:thing :to type:, but valid :nonetheless:

Use this code I put up below I think using this function your problem will be solved.
string s = "Hello:grinning: , how are you?:kissing_heart: Are you fine?:bouquet:";
string rmv = ""; string remove = "";
int i = 0; int k = 0;
A:
rmv = "";
for (i = k; i < s.Length; i++)
{
if (Convert.ToString(s[i]) == ":")
{
for (int j = i + 1; j < s.Length; j++)
{
if (Convert.ToString(s[j]) != ":")
{
rmv += s[j];
}
else
{
remove += rmv + ",";
i = j;
k = j + 1;
goto A;
}
}
}
}
string[] str = remove.Split(',');
for (int x = 0; x < str.Length-1; x++)
{
s = s.Replace(Convert.ToString(":" + str[x] + ":"), "");
}
Console.WriteLine(s);
Console.ReadKey();

I'd use extension method like this:
public static class Helper
{
public static string MyReplace(this string dirty, char separator)
{
string newText = "";
bool replace = false;
for (int i = 0; i < dirty.Length; i++)
{
if(dirty[i] == separator) { replace = !replace ; continue;}
if(replace ) continue;
newText += dirty[i];
}
return newText;
}
}
Usage:
richTextBox2.Text = richTextBox2.Text.MyReplace(':');
This method show be better in terms of performance compare to one with Regex

I would split the text with the ':' and then build the string excluding the found emoji names.
const char marker = ':';
var textSections = text.Split(marker);
var emojiRemovedText = string.Empty;
var notMatchedCount = 0;
textSections.ToList().ForEach(section =>
{
if (emojiNames.Contains(section))
{
notMatchedCount = 0;
}
else
{
if (notMatchedCount++ > 0)
{
emojiRemovedText += marker.ToString();
}
emojiRemovedText += section;
}
});

Retrieve String Containing Specific substring C#

I am having an output in string format like following :
"ABCDED 0000A1.txt PQRSNT 12345"
I want to retreieve substring(s) having .txt in above string. e.g. For above it should return 0000A1.txt.
Thanks

You can either split the string at whitespace boundaries like it's already been suggested or repeatedly match the same regex like this:
var input = "ABCDED 0000A1.txt PQRSNT 12345 THE.txt FOO";
var match = Regex.Match (input, #"\b([\w\d]+\.txt)\b");
while (match.Success) {
Console.WriteLine ("TEST: {0}", match.Value);
match = match.NextMatch ();
}

Split will work if it the spaces are the seperator. if you use oter seperators you can add as needed
string input = "ABCDED 0000A1.txt PQRSNT 12345";
string filename = input.Split(' ').FirstOrDefault(f => System.IO.Path.HasExtension(f));
filname = "0000A1.txt" and this will work for any extension

You may use c#, regex and pattern, match :)
Here is the code, plug it in try. Please comment.
string test = "afdkljfljalf dkfjd.txt lkjdfjdl";
string ffile = Regex.Match(test, #"\([a-z0-9])+.txt").Groups[1].Value;
Console.WriteLine(ffile);
Reference: regexp

I did something like this:
string subString = "";
char period = '.';
char[] chArString;
int iSubStrIndex = 0;
if (myString != null)
{
chArString = new char[myString.Length];
chArString = myString.ToCharArray();
for (int i = 0; i < myString.Length; i ++)
{
if (chArString[i] == period)
iSubStrIndex = i;
}
substring = myString.Substring(iSubStrIndex);
}
Hope that helps.

First split your string in array using
char[] whitespace = new char[] { ' ', '\t' };
string[] ssizes = myStr.Split(whitespace);
Then find .txt in array...
// Find first element starting with .txt.
//
string value1 = Array.Find(array1,
element => element.Contains(".txt", StringComparison.Ordinal));
Now your value1 will have the "0000A1.txt"
Happy coding.

C# Split string into array based on prior character

I need to take a string and split it into an array based on the type of charcter not matching they proceeding it.
So if you have "asd fds 1.4#3" this would split into array as follows
stringArray[0] = "asd";
stringArray[1] = " ";
stringArray[2] = "fds";
stringArray[3] = " ";
stringArray[4] = "1";
stringArray[5] = ".";
stringArray[6] = "4";
stringArray[7] = "#";
stringArray[8] = "3";
Any recomendations on the best way to acheive this? Of course I could create a loop based on .ToCharArray() but was looking for a better way to achieve this.
Thank you

Using a combination of Regular Expressions and link you can do the following.
using System.Text.RegularExpressions;
using System.Linq;
var str="asd fds 1.4#3";
var regex=new Regex("([A-Za-z]+)|([0-9]+)|([.#]+)|(.+?)");
var result=regex.Matches(str).OfType<Match>().Select(x=>x.Value).ToArray();
Add additional capture groups to capture other differences. The last capture (.+?) is a non greedy everything else. So every item in this capture will be considered different (including the same item twice)
Update - new revision of regex
var regex=new Regex(#"(?:[A-Za-z]+)|(?:[0-9]+)|(?:[#.]+)|(?:(?:(.)\1*)+?)");
This now uses non capturing groups so that \1 can be used in the final capture. This means that the same character will be grouped if its in then catch all group.
e.g. before the string "asd fsd" would create 4 strings (each space would be considered different) now the result is 3 strings as 2 adjacent spaces are combined

Use regex:
var mc = Regex.Matches("asd fds 1.4#3", #"([a-zA-Z]+)|.");
var res = new string[mc.Count];
for (var i = 0; i < mc.Count; i++)
{
res[i] = mc[i].Value;
}

This program produces exactly output you want, but I am not sure wether it's generic enaugh for your goal.
class Program
{
private static void Main(string[] args)
{
var splited = Split("asd fds 1.4#3").ToArray();
}
public static IEnumerable<string> Split(string text)
{
StringBuilder result = new StringBuilder();
foreach (var ch in text)
{
if (char.IsLetter(ch))
{
result.Append(ch);
}
else
{
yield return result.ToString();
result.Clear();
yield return ch.ToString(CultureInfo.InvariantCulture);
}
}
}
}

Find substring ignoring specified characters

Do any of you know of an easy/clean way to find a substring within a string while ignoring some specified characters to find it. I think an example would explain things better:
string: "Hello, -this- is a string"
substring to find: "Hello this"
chars to ignore: "," and "-"
found the substring, result: "Hello, -this"
Using Regex is not a requirement for me, but I added the tag because it feels related.
Update:
To make the requirement clearer: I need the resulting substring with the ignored chars, not just an indication that the given substring exists.
Update 2:
Some of you are reading too much into the example, sorry, i'll give another scenario that should work:
string: "?A&3/3/C)412&"
substring to find: "A41"
chars to ignore: "&", "/", "3", "C", ")"
found the substring, result: "A&3/3/C)41"
And as a bonus (not required per se), it will be great if it's also not safe to assume that the substring to find will not have the ignored chars on it, e.g.: given the last example we should be able to do:
substring to find: "A3C412&"
chars to ignore: "&", "/", "3", "C", ")"
found the substring, result: "A&3/3/C)412&"
Sorry if I wasn't clear before, or still I'm not :).
Update 3:
Thanks to everyone who helped!, this is the implementation I'm working with for now:
http://www.pastebin.com/pYHbb43Z
An here are some tests:
http://www.pastebin.com/qh01GSx2
I'm using some custom extension methods I'm not including but I believe they should be self-explainatory (I will add them if you like)
I've taken a lot of your ideas for the implementation and the tests but I'm giving the answer to #PierrOz because he was one of the firsts, and pointed me in the right direction.
Feel free to keep giving suggestions as alternative solutions or comments on the current state of the impl. if you like.

in your example you would do:
string input = "Hello, -this-, is a string";
string ignore = "[-,]*";
Regex r = new Regex(string.Format("H{0}e{0}l{0}l{0}o{0} {0}t{0}h{0}i{0}s{0}", ignore));
Match m = r.Match(input);
return m.Success ? m.Value : string.Empty;
Dynamically you would build the part [-, ] with all the characters to ignore and you would insert this part between all the characters of your query.
Take care of '-' in the class []: put it at the beginning or at the end
So more generically, it would give something like:
public string Test(string query, string input, char[] ignorelist)
{
string ignorePattern = "[";
for (int i=0; i<ignoreList.Length; i++)
{
if (ignoreList[i] == '-')
{
ignorePattern.Insert(1, "-");
}
else
{
ignorePattern += ignoreList[i];
}
}
ignorePattern += "]*";
for (int i = 0; i < query.Length; i++)
{
pattern += query[0] + ignorepattern;
}
Regex r = new Regex(pattern);
Match m = r.Match(input);
return m.IsSuccess ? m.Value : string.Empty;
}

Here's a non-regex string extension option:
public static class StringExtensions
{
public static bool SubstringSearch(this string s, string value, char[] ignoreChars, out string result)
{
if (String.IsNullOrEmpty(value))
throw new ArgumentException("Search value cannot be null or empty.", "value");
bool found = false;
int matches = 0;
int startIndex = -1;
int length = 0;
for (int i = 0; i < s.Length && !found; i++)
{
if (startIndex == -1)
{
if (s[i] == value[0])
{
startIndex = i;
++matches;
++length;
}
}
else
{
if (s[i] == value[matches])
{
++matches;
++length;
}
else if (ignoreChars != null && ignoreChars.Contains(s[i]))
{
++length;
}
else
{
startIndex = -1;
matches = 0;
length = 0;
}
}
found = (matches == value.Length);
}
if (found)
{
result = s.Substring(startIndex, length);
}
else
{
result = null;
}
return found;
}
}

EDIT: here's an updated solution addressing the points in your recent update. The idea is the same except if you have one substring it will need to insert the ignore pattern between each character. If the substring contains spaces it will split on the spaces and insert the ignore pattern between those words. If you don't have a need for the latter functionality (which was more in line with your original question) then you can remove the Split and if checking that provides that pattern.
Note that this approach is not going to be the most efficient.
string input = #"foo ?A&3/3/C)412& bar A341C2";
string substring = "A41";
string[] ignoredChars = { "&", "/", "3", "C", ")" };
// builds up the ignored pattern and ensures a dash char is placed at the end to avoid unintended ranges
string ignoredPattern = String.Concat("[",
String.Join("", ignoredChars.Where(c => c != "-")
.Select(c => Regex.Escape(c)).ToArray()),
(ignoredChars.Contains("-") ? "-" : ""),
"]*?");
string[] substrings = substring.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
string pattern = "";
if (substrings.Length > 1)
{
pattern = String.Join(ignoredPattern, substrings);
}
else
{
pattern = String.Join(ignoredPattern, substring.Select(c => c.ToString()).ToArray());
}
foreach (Match match in Regex.Matches(input, pattern))
{
Console.WriteLine("Index: {0} -- Match: {1}", match.Index, match.Value);
}
Try this solution out:
string input = "Hello, -this- is a string";
string[] searchStrings = { "Hello", "this" };
string pattern = String.Join(#"\W+", searchStrings);
foreach (Match match in Regex.Matches(input, pattern))
{
Console.WriteLine(match.Value);
}
The \W+ will match any non-alphanumeric character. If you feel like specifying them yourself, you can replace it with a character class of the characters to ignore, such as [ ,.-]+ (always place the dash character at the start or end to avoid unintended range specifications). Also, if you need case to be ignored use RegexOptions.IgnoreCase:
Regex.Matches(input, pattern, RegexOptions.IgnoreCase)
If your substring is in the form of a complete string, such as "Hello this", you can easily get it into an array form for searchString in this way:
string[] searchString = substring.Split(new[] { ' ' },
StringSplitOptions.RemoveEmptyEntries);

This code will do what you want, although I suggest you modify it to fit your needs better:
string resultString = null;
try
{
resultString = Regex.Match(subjectString, "Hello[, -]*this", RegexOptions.IgnoreCase).Value;
}
catch (ArgumentException ex)
{
// Syntax error in the regular expression
}

You could do this with a single Regex but it would be quite tedious as after every character you would need to test for zero or more ignored characters. It is probably easier to strip all the ignored characters with Regex.Replace(subject, "[-,]", ""); then test if the substring is there.
Or the single Regex way
Regex.IsMatch(subject, "H[-,]*e[-,]*l[-,]*l[-,]*o[-,]* [-,]*t[-,]*h[-,]*i[-,]*s[-,]*")

Here's a non-regex way to do it using string parsing.
private string GetSubstring()
{
string searchString = "Hello, -this- is a string";
string searchStringWithoutUnwantedChars = searchString.Replace(",", "").Replace("-", "");
string desiredString = string.Empty;
if(searchStringWithoutUnwantedChars.Contains("Hello this"))
desiredString = searchString.Substring(searchString.IndexOf("Hello"), searchString.IndexOf("this") + 4);
return desiredString;
}

You could do something like this, since most all of these answer require rebuilding the string in some form.
string1 is your string you want to look through
//Create a List(Of string) that contains the ignored characters'
List<string> ignoredCharacters = new List<string>();
//Add all of the characters you wish to ignore in the method you choose
//Use a function here to get a return
public bool subStringExist(List<string> ignoredCharacters, string myString, string toMatch)
{
//Copy Your string to a temp
string tempString = myString;
bool match = false;
//Replace Everything that you don't want
foreach (string item in ignoredCharacters)
{
tempString = tempString.Replace(item, "");
}
//Check if your substring exist
if (tempString.Contains(toMatch))
{
match = true;
}
return match;
}

You could always use a combination of RegEx and string searching
public class RegExpression {
public static void Example(string input, string ignore, string find)
{
string output = string.Format("Input: {1}{0}Ignore: {2}{0}Find: {3}{0}{0}", Environment.NewLine, input, ignore, find);
if (SanitizeText(input, ignore).ToString().Contains(SanitizeText(find, ignore)))
Console.WriteLine(output + "was matched");
else
Console.WriteLine(output + "was NOT matched");
Console.WriteLine();
}
public static string SanitizeText(string input, string ignore)
{
Regex reg = new Regex("[^" + ignore + "]");
StringBuilder newInput = new StringBuilder();
foreach (Match m in reg.Matches(input))
{
newInput.Append(m.Value);
}
return newInput.ToString();
}
}
Usage would be like
RegExpression.Example("Hello, -this- is a string", "-,", "Hello this"); //Should match
RegExpression.Example("Hello, -this- is a string", "-,", "Hello this2"); //Should not match
RegExpression.Example("?A&3/3/C)412&", "&/3C\\)", "A41"); // Should match
RegExpression.Example("?A&3/3/C) 412&", "&/3C\\)", "A41"); // Should not match
RegExpression.Example("?A&3/3/C)412&", "&/3C\\)", "A3C412&"); // Should match
Output
Input: Hello, -this- is a string
Ignore: -,
Find: Hello this
was matched
Input: Hello, -this- is a string
Ignore: -,
Find: Hello this2
was NOT matched
Input: ?A&3/3/C)412&
Ignore: &/3C)
Find: A41
was matched
Input: ?A&3/3/C) 412&
Ignore: &/3C)
Find: A41
was NOT matched
Input: ?A&3/3/C)412&
Ignore: &/3C)
Find: A3C412&
was matched

Replace all Special Characters in a string IN C#

I would like to find all special characters in a string and replace with a Hyphen (-)
I am using the below code
string content = "foo,bar,(regular expression replace) 123";
string pattern = "[^a-zA-Z]"; //regex pattern
string result = System.Text.RegularExpressions.Regex.Replace(content,pattern, "-");
OutPut
foo-bar--regular-expression-replace----
I am getting multiple occurrence of hyphen (---) in the out put.
I would like to get some thing like this
foo-bar-regular-expression-replace
How do I achieve this
Any help would be appreciated
Thanks
Deepu

why not just do this:
public static string ToSlug(this string text)
{
StringBuilder sb = new StringBuilder();
var lastWasInvalid = false;
foreach (char c in text)
{
if (char.IsLetterOrDigit(c))
{
sb.Append(c);
lastWasInvalid = false;
}
else
{
if (!lastWasInvalid)
sb.Append("-");
lastWasInvalid = true;
}
}
return sb.ToString().ToLowerInvariant().Trim();
}

Try the pattern: "[^a-zA-Z]+" - i.e. replace one-or-more non-alpha (you might allow numeric, though?).

Wouldn't this work?
string pattern = "[^a-zA-Z]+";