Develop Reference

How to remove only certain substrings from a string?

Using C#, I have a string that is a SQL script containing multiple queries. I want to remove sections of the string that are enclosed in single quotes. I can do this using Regex.Replace, in this manner:
string test = "Only 'together' can we turn him to the 'dark side' of the Force";
test = Regex.Replace(test, "'[^']*'", string.Empty);
Results in: "Only can we turn him to the of the Force"
What I want to do is remove the substrings between quotes EXCEPT for substrings containing a specific substring. For example, using the string above, I want to remove the quoted substrings except for those that contain "dark," such that the resulting string is:
Results in: "Only can we turn him to the 'dark side' of the Force"
How can this be accomplished using Regex.Replace, or perhaps by some other technique? I'm currently trying a solution that involves using Substring(), IndexOf(), and Contains().
Note: I don't care if the single quotes around "dark side" are removed or not, so the result could also be: "Only can we turn him to the dark side of the Force." I say this because a solution using Split() would remove all the single quotes.
Edit: I don't have a solution yet using Substring(), IndexOf(), etc. By "working on," I mean I'm thinking in my head how this can be done. I have no code, which is why I haven't posted any yet. Thanks.
Edit: VKS's solution below works. I wasn't escaping the \b the first attempt which is why it failed. Also, it didn't work unless I included the single quotes around the whole string as well.
test = Regex.Replace(test, "'(?![^']*\\bdark\\b)[^']*'", string.Empty);

'(?![^']*\bdark\b)[^']*'
Try this.See demo.Replace by empty string.You can use lookahead here to check if '' contains a word dark.
https://www.regex101.com/r/rG7gX4/12

While vks's solution works, I'd like to demonstrate a different approach:
string test = "Only 'together' can we turn him to the 'dark side' of the Force";
test = Regex.Replace(test, #"'[^']*'", match => {
if (match.Value.Contains("dark"))
return match.Value;
// You can add more cases here
return string.Empty;
});
Or, if your condition is simple enough:
test = Regex.Replace(test, #"'[^']*'", match => match.Value.Contains("dark")
? match.Value
: string.Empty
);
That is, use a lambda to provide a callback for the replacement. This way, you can run arbitrary logic to replace the string.

some thing like this would work. you can add all strings you want to keep into the excludedStrings array
string test = "Only 'together' can we turn him to the 'dark side' of the Force";
var excludedString = new string[] { "dark side" };
int startIndex = 0;
while ((startIndex = test.IndexOf('\'', startIndex)) >= 0)
{
var endIndex = test.IndexOf('\'', startIndex + 1);
var subString = test.Substring(startIndex, (endIndex - startIndex) + 1);
if (!excludedString.Contains(subString.Replace("'", "")))
{
test = test.Remove(startIndex, (endIndex - startIndex) + 1);
}
else
{
startIndex = endIndex + 1;
}
}

Another method through regex alternation operator |.
#"('[^']*\bdark\b[^']*')|'[^']*'"
Then replace the matched character with $1
DEMO
string str = "Only 'together' can we turn him to the 'dark side' of the Force";
string result = Regex.Replace(str, #"('[^']*\bdark\b[^']*')|'[^']*'", "$1");
Console.WriteLine(result);
IDEONE
Explanation:
(...) called capturing group.
'[^']*\bdark\b[^']*' would match all the single quoted strings which contains the substring dark . [^']* matches any character but not of ', zero or more times.
('[^']*\bdark\b[^']*'), because the regex is within a capturing group, all the matched characters are stored inside the group index 1.
| Next comes the regex alternation operator.
'[^']*' Now this matches all the remaining (except the one contains dark) single quoted strings. Note that this won't match the single quoted string which contains the substring dark because we already matched those strings with the pattern exists before to the | alternation operator.
Finally replacing all the matched characters with the chars inside group index 1 will give you the desired output.

I made this attempt that I think you were thinking about (some solution using split, Contain, ... without regex)
string test = "Only 'together' can we turn him to the 'dark side' of the Force";
string[] separated = test.Split('\'');
string result = "";
for (int i = 0; i < separated.Length; i++)
{
string str = separated[i];
str = str.Trim(); //trim the tailing spaces
if (i % 2 == 0 || str.Contains("dark")) // you can expand your condition
{
result += str+" "; // add space after each added string
}
}
result = result.Trim(); //trim the tailing space again

Remove a single space from a string

"How do I do this? "
Let's say I have this string. How do I remove only one space from the end? The code shown below gives me an error saying the count is out of range.
string s = "How do I do this? ";
s = s.Remove(s.Length, 1);

You just have to use this instead :
string s = "How do I do this? ";
s = s.Remove(s.Length-1, 1);
As stated here:
Remove(Int32) Returns a new string in which all the characters in the current
instance, beginning at a specified position and continuing through the
last position, have been deleted.
In an array, positions range from 0 to Length-1, hence the compiler error.

The indexing in C# are zero-based.
s = s.Remove(s.Length - 1, 1);

Just do a substring from the first character (chars are 0-based in string) and get number of chars less the string length by 1
s = s.Substring(0, s.Length - 1);

This is a little safer, just in case the last character is not a space
string s = "How do I do this? ";
s = Regex.Replace(s, #" $", "")

You have to write something in the lines of
string s = "How do I do this?
s = s.Remove(s.Length-1, 1);
Reason being that in C# when referring to indexes in arrays the first element is always at position 0 and end at Length - 1. The Length generally tells you how long a string is but doesn't map to the actual array index.

Another way to do it is;
string s = "How do I do this? ";
s=s.SubString(0,s.Length-1);
Additional :
If you would like do some additional checking for the last character being a space or anything,you can do it in this way;
string s = "How do I do this? a";//Just for example,i've added a 'a' at the end.
int index = s.Length - 1;//Get last Char index.
if (index > 0)//If index exists.
{
if (s[index] == ' ')//If the character at 'index' is a space.
{
MessageBox.Show("Its a space.");
}
else if (char.IsLetter(s[index]))//If the character at 'index' is a letter.
{
MessageBox.Show("Its a letter.");
}
else if(char.IsDigit(s[index]))//If the character at 'index' is a digit.
{
MessageBox.Show("Its a digit.");
}
}
This gives you a MessageBox with message "Its a letter".
One more thing that might be helpful,if you want to create a string with equal no. of spaces between each word,then you can try this.
string s = "How do I do this? ";
string[] words = s.Split(new char[] {' '},StringSplitOptions.RemoveEmptyEntries);//Break the string into individual words.
StringBuilder sb = new StringBuilder();
foreach (string word in words)//Iterate through each word.
{
sb.Append(word);//Append the word.
sb.Append(" ");//Append a single space.
}
MessageBox.Show(sb.ToString());//Resultant string 'sb.ToString()'.
This gives you "How do I do this? " (equal spaces between words).

Cut the string to be <= 80 characters AND must keep the words without cutting them

I am new to C#, but I have a requirement to cut the strings to be <= 80 characters AND they must keep the words integrity (without cutting them)
Examples
Before: I have a requirenment to cut the strings to be <= 80 characters AND must keep the words without cutting them (length=108)
After: I have a requirenment to cut the strings to be <= 80 characters AND must keep (length=77)
Before: requirenment to cut the strings to be <= 80 characters AND must keep the words without cutting them (length=99)
After: requirenment to cut the strings to be <= 80 characters AND must keep the words (length=78)
Before: I have a requirenment the strings to be <= 80 characters AND must keep the words without cutting them (length=101)
After: I have a requirenment the strings to be <= 80 characters AND must keep the words (length=80)
I want to use the RegEx, but I don't know anything about the regex. It would be a hassle to to the else-if's for this.
I would appreciate if you could point me to the right article which I could use to create this expression.
this is my function that I want to cut to one line:
public String cutTitleto80(String s){
String[] words = Regex.Split(s, "\\s+");
String finalResult = "";
foreach (String word in words)
{
String tmp = finalResult + " " + word;
if (tmp.Length > 80)
{
return finalResult;
}
finalResult = tmp;
}
return finalResult;
}

Try
^(.{0,80})(?: |$)
This is a capturing greedy match which must be followed by a space or end of string. You could also use a zero-width lookahead assertion, as in
^.{0,80}(?= |$)
If you use a live test tool like http://regexhero.net/tester/ it's pretty cool, you can actually see it jump back to the word boundary as you type beyond 80 characters.
And here's one which will simply truncate at the 80th character if there are no word boundaries (spaces) to be found:
^(.{1,80}(?: |$)|.{80})

Here's an approach without using Regex: just split the string (however you'd like) into whatever you consider "words" to be. Then, just start concatenating them together using a StringBuilder, checking for your desired length, until you can't add the next "word". Then, just return the string that you have built up so far.
(Untested code ahead)
public string TruncateWithPreservation(string s, int len)
{
string[] parts = s.Split(' ');
StringBuilder sb = new StringBuilder();
foreach (string part in parts)
{
if (sb.Length + part.Length > len)
break;
sb.Append(' ');
sb.Append(part);
}
return sb.ToString();
}

string truncatedText = text.Substring(0, 80); // truncate to 80 characters
if (text[80] != ' ') // don't remove last word if a space occurs after it in the original string (in other words, last word is already complete)
truncatedText = truncatedText.Substring(0, truncatedText.LastIndexOf(' ')); // remove any cut-off words
Updated to fix issue from comments where last word could get cut off even if it is complete.

This isn't using regex but this is how I would do it:
Use String.LastIndexOf to get the last space before the 81st char.
If the 81th char is a space then take it until 80.
if it returns a number > -1 cut it off there.
If it's -1 you-have-a-really-long-word-or-someone-messing-with-the-system so you do wathever you like.

c# Best way to break up a long string

This question is not related to:
Best way to break long strings in C# source code
Which is about source, this is about processing long outputs. If someone enters:
WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW
As a comment, it breaks the container and makes the entire page really wide. Is there any clever regexp that can say, define a maximum word length of 20 chars and then force a whitespace character?
Thanks for any help!

There's probably no need to involve regexes in something this simple. Take this extension method:
public static string Abbreviate(this string text, int length) {
if (text.Length <= length) {
return text;
}
char[] delimiters = new char[] { ' ', '.', ',', ':', ';' };
int index = text.LastIndexOfAny(delimiters, length - 3);
if (index > (length / 2)) {
return text.Substring(0, index) + "...";
}
else {
return text.Substring(0, length - 3) + "...";
}
}
If the string is short enough, it's returned as-is. Otherwise, if a "word boundary" is found in the second half of the string, it's "gracefully" cut off at that point. If not, it's cut off the hard way at just under the desired length.
If the string is cut off at all, an ellipsis ("...") is appended to it.
If you expect the string to contain non-natural-language constructs (such as URLs) you 'd need to tweak this to ensure nice behavior in all circumstances. In that case working with a regex might be better.

You could try using a regular expression that uses a positive look-ahead like this:
string outputStr = Regex.Replace(inputStr, #"([\S]{20}(?=\S+))", "$1\n");
This should "insert" a line break into all words that are longer than 20 characters.

Yes you can use this one regex
string pattern = #"^([\w]{1,20})$";
this regex allow to enter not more than 20 characters
string strRegex = #"^([\w]{1,20})$";
string strTargetString = #"asdfasfasfasdffffff";
if(Regex.IsMatch(strTargetString, strRegex))
{
//do something
}
If you need only lenght constraint you should use this regex
^(.{1,20})$
because the \w is match only
alphanumeric and underscore symbol

How to remove words based on a word count

Here is what I'm trying to accomplish. I have an object coming back from
the database with a string description. This description can be up to 1000
characters long, but we only want to display a short view of this. So I coded
up the following, but I'm having trouble in actually removing the number of
words after the regular expression finds the total count of words. Does anyone
have good way of dispalying the words which are less than the Regex.Matches?
Thanks!
if (!string.IsNullOrEmpty(myObject.Description))
{
string original = myObject.Description;
MatchCollection wordColl = Regex.Matches(original, #"[\S]+");
if (wordColl.Count < 70) // 70 words?
{
uxDescriptionDisplay.Text =
string.Format("<p>{0}</p>", myObject.Description);
}
else
{
string shortendText = original.Remove(200); // 200 characters?
uxDescriptionDisplay.Text =
string.Format("<p>{0}</p>", shortendText);
}
}
EDIT:
So this is what I got working on my own:
else
{
int count = 0;
StringBuilder builder = new StringBuilder();
string[] workingText = original.Split(' ');
foreach (string word in workingText)
{
if (count < 70)
{
builder.AppendFormat("{0} ", word);
}
count++;
}
string shortendText = builder.ToString();
}
It's not pretty, but it worked. I would call it a pretty naive way of doing this. Thanks for all of the suggestions!

I would opt to go by a strict character count rather than a word count because you might happen to have a lot of long words.
I might do something like (pseudocode)
if text.Length > someLimit
find first whitespace after someLimit (or perhaps last whitespace immediately before)
display substring of text
else
display text
Possible code implementation:
string TruncateText(string input, int characterLimit)
{
if (input.Length > characterLimit)
{
// find last whitespace immediately before limit
int whitespacePosition = input.Substring(0, characterLimit).LastIndexOf(" ");
// or find first whitespace after limit (what is spec?)
// int whitespacePosition = input.IndexOf(" ", characterLimit);
if (whitespacePosition > -1)
return input.Substring(0, whitespacePosition);
}
return input;
}

One method, if you're using at least C#3.0, would be a LINQ like the following. This is provided you're going strictly by word count, not character count.
if (wordColl.Count > 70)
{
foreach (var subWord in wordColl.Cast<Match>().Select(r => r.Value).Take(70))
{
//Build string here out of subWord
}
}
I did a test using a simple Console.WriteLine with your Regex and your question body (which is over 70 words, it turns out).

You can use Regex Capture Groups to hold the match and access it later.
For your application, I'd recommend instead simply splitting the string by spaces and returning the first n elements of the array:
if (!string.IsNullOrEmpty(myObject.Description))
{
string original = myObject.Description;
string[] words = original.Split(' ');
if (words.Length < 70)
{
uxDescriptionDisplay.Text =
string.Format("<p>{0}</p>", original);
}
else
{
string shortDesc = string.Empty;
for(int i = 0; i < 70; i++) shortDesc += words[i] + " ";
uxDescriptionDisplay.Text =
string.Format("<p>{0}</p>", shortDesc.Trim());
}
}

Are you wanting to remove 200 characters or start truncating at the 200th character? When you call original.Remove(200) you are indexing the start of the truncation at the 200th character. This is how you use Remove() for a certain number of characters to remove:
string shortendText = original.Remove(0,200);
This starts at the first character and removes 200 starting with that one. Which I imagine that's not what you're trying to do since you're shortening a description. That's merely the correct way to use Remove().
Instead of using Regex matchcollections why not just split the string? It's a lot easier and straight forward. You can set the delimiter to a space character and split that way. Not sure if that completely fixes your need but it just might. I'm not sure what your data looks like in the description. But you split this way:
String[] wordArray = original.Split(' ');
From there you can determine the word count with wordArray's Length property value.

If I was you I would go by characters as you may have many one letter words or many long words in your text.
Go through until characters <= your limit, then either find the next space and then add these characters to a new string (possibly using the SubString method) or take these characters and add a few full stops, then make a new string The later could be unproffessional I suppose.