Develop Reference

Regular expression with specific word boundary

Let's say I have a string of type
(Price+Discounted_Price)*2-Max.Price
and a dictionary containing what to replace for each element
Price: A1 Discounted_Price: A2 Max.Price:A3
How can I replace exactly each phrases, without touching the other. Meaning search for Price should not modify Price in Discounted_Price. The result should be (A1+A2)*2-A3 and not (A1+Discounted_A1) - Max.A1 or anything else
Thank you.

If your variables can consist of alphanumeric/underscore/dot characters, you can match them with [\w.]+ regex pattern, and add boundaries that include .:
using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
public class Test
{
public static void Main()
{
var s = "(Price+Discounted_Price)*2-Max.Price";
var dct = new Dictionary<string, string>();
dct.Add("Price", "A1");
dct.Add("Discounted_Price", "A2");
dct.Add("Max.Price","A3");
var res = Regex.Replace(s, #"(?<![\w.])[\w.]+(?![\w.])", // Find all matches with the regex inside s
x => dct.ContainsKey(x.Value) ? // Does the dictionary contain the key that equals the matched text?
dct[x.Value] : // Use the value for the key if it is present to replace current match
x.Value); // Otherwise, insert the match found back into the result
Console.WriteLine(res);
}
}
See the IDEONE demo
The (?<![\w.]) negative lookbehind fails the match if the match is preceded with a word or a dot char, and the (?![\w.]) negative lookahead will fail the match if it is followed with a word or dot char.
Note that [\w.]+ allows a dot in the leading and trailing positions, thus, you might want to replace it with \w+(?:\.\w+)* and use as #"(?<![\w.])\w+(?:\.\w+)*(?![\w.])".
UPDATE
Since you have already extracted the keywords to replace as a list, you need to use a more sophisticated word boundary excluding dots:
var listAbove = new List<string> { "Price", "Discounted_Price", "Max.Price" };
var result = s;
foreach (string phrase in listAbove)
{
result = Regex.Replace(result, #"\b(?<![\w.])" + Regex.Escape(phrase) + #"\b(?![\w.])", dct[phrase]);
}
See IDEONE demo.

For word boundaries, you can use \b
Use: \bPrice\b
But this will replace Price in Max.Price.
Maybe you want to use regular string replace with:
"Price+" --> A1 + "+"
Example:
string test = "(Price+Discounted_Price)*2-Max.Price";
string a1 = "7";
string a2 = "3";
string a3 = "4";
test = test.Replace("(Price", "(" + a1);
test = test.Replace("Discounted_Price", a2);
test = test.Replace("Max.Price", a3);
Result:
test is: (7+3)*2-4

Search Strings for particular sequence

fairly new to c#, im looking for a way to search a string for a particular sequence:
string mytext = "I want to find t56b45 in a string"
In the above example i would like to search mytext for the position of "t" but only when it is followed by any two numeric chars and a "b" followed by any two numeric chars. If i find a "t"+any two numeric values+"b"+any two numeric values then i would like to create a sub string up to that position ie. the result string will read "I want to find"

Use a Regex:
using System;
using System.Text.RegularExpressions;
public class Program
{
public static void Main()
{
// \s : Matches a space
// t : Exact match t
// \d{2} : Any digit, 2 repetition
// t : Exact match b
// \d{2} : Any digit, 2 repetition
var match = Regex.Match("I want to find t56b45 in a string", #".*(?=\st\d{2}b\d{2})");
if(match.Success)
Console.WriteLine("\"" + match.Value + "\"");
else
Console.WriteLine("Nothing found.");
// Outputs: "I want to find"
}
}
Fiddle:
https://dotnetfiddle.net/kguwDW

So this is the code i ended up using, seems to get the job done and ignore the case
var tempmatch = Regex.Match(TempCleaned, "(?i)y[0-9]+(?i)z[0-9]+");
if (tempmatch.Success)
{
//clean all text from YxxZxx
string NewName = TempCleaned.Substring(0, tempmatch.Index -1);

Regex Matchcollection groups

I already tried two days to solve the Problem, that I have a MatchCollection. In the patter is a Group and I want to have a list with the Solutions of the Group (there were two or more Solutions).
string input = "<tr><td>Mi, 09.09.15</td><td>1</td><td>PK</td><td>E</td><td>123</td><td></td></tr><tr><td>Mi, 09.09.15</td><td>2</td><td>ER</td><td>ER</td><td>234</td><td></td></tr>";
string Patter2 = "^<tr>$?<td>$?[D-M][i-r],[' '][0-3][1-9].[0-1][1-9].[0-9][0-9]$?</td>$?<td>$?([1-9][0-2]?)$?</td>$?";
Regex r2 = new Regex(Patter2);
MatchCollection mc2 = r2.Matches(input);
foreach (Match match in mc2)
{
GroupCollection groups = match.Groups;
string s = groups[1].Value;
Datum2.Text = s;
}
But only the last match (2) appears in the TextBox "Datum2".
I know that I have to use e.g. a listbox, but the Groups[1].Value is a string...
Thanks for your help and time.
Dieter

First thing you need to correct in the code is Datum2.Text = s; would overwrite the text in Datum2 if it were more than one match.
Now, about your regex,
^ forces a match at the begging of the line, so there is really only 1 match. If you remove it, it'll match twice.
I can't seem to understand what was intended with $? all over the pattern (just take them out).
[' '] matches "either a quote, a space or a quote (no need to repeat characters in a character class.
All dots in [0-3][1-9].[0-1][1-9].[0-9][0-9] need to be escaped. A dot matches any character otherwise.
[0-1][1-9] matches all months except "10". The second character shoud be [0-9] (or \d).
Code:
string input = "<tr><td>Mi, 09.09.15</td><td>1</td><td>PK</td><td>E</td><td>123</td><td></td></tr><tr><td>Mi, 09.09.15</td><td>2</td><td>ER</td><td>ER</td><td>234</td><td></td></tr>";
string Patter2 = "<tr><td>[D-M][i-r],[' ][0-3][0-9]\\.[0-1][0-9]\\.[0-9][0-9]</td><td>([1-9][0-2]?)</td>";
Regex r2 = new Regex(Patter2);
MatchCollection mc2 = r2.Matches(input);
string s= "";
foreach (Match match in mc2)
{
GroupCollection groups = match.Groups;
s = s + " " + groups[1].Value;
}
Datum2.Text = s;
Output:
1 2
DEMO
You should know that regex is not the tool to parse HTML. It'll work for simple cases, but for real cases do consider using HTML Agility Pack

Regular Expression without braces

i have the following sample cases :
1) "Sample"
2) "[10,25]"
I want to form a(only one) regular expression pattern, to which the above examples are passed returns me "Sample" and "10,25".
Note: Input strings do not include Quotes.
I came up with the following expression (?<=\[)(.*?)(?=\]), this satisfies the second case and retreives me only "10,25" but when the first case is matched it returns me blank. I want "Sample" to be returned? can anyone help me.
C#.

here you go, a small regex using a positive lookbehind, sometime these are very handy
Regex
(?<=^|\[)([\w,]+)
Test string
Sample
[10,25]
Result
MATCH 1
[0-6] Sample
MATCH 2
[8-13] 10,25
try at regex101.com
if " is included in your original string, use this regex, this will look for " mark as well, you may choose to remove ^| from lookup if " mark is always included or you may choose to leave it as it is if your text has combination of with and without " marks
Regex
(?<=^|\[|\")([\w,]+)
try at regex101.com

As far as I can tell, the below regex should help:
Regex regex = new Regex(#"^\w+|[[](\w)+\,(\w)+[]]$");
This will match multiple words, or 2 words (alphanumeric) separated by commas and inside square brackets.

One Java example:
// String input = "Sample";
String input = "[10,25]";
String text = "[^,\\[\\]]+";
Pattern pMod = Pattern.compile("(" + text + ")|(?>\\[(" + text + "," + text + ")\\])");
Matcher mMod = pMod.matcher(input);
while (mMod.find()) {
if(mMod.group(1) != null) {
System.out.println(mMod.group(1));
}
if(mMod.group(2)!=null) {
System.out.println(mMod.group(2));
}
}
if input is "[hello&bye,25|35]", then the output is hello&bye,25|35

c# Regex question

I have a problem dealing with the # symbol in Regex, I am trying to remove #sometext
from a text string can't seem to find anywhere where it uses the # as a literal. I have tried myself but doesn't remove the word from the string. Any ideas?
public string removeAtSymbol(string input)
{
Regex findWords = new Regex(______);//Find the words like "#text"
Regex[] removeWords;
string test = input;
MatchCollection all = findWords.Matches(test);
removeWords = new Regex[all.Count];
int index = 0;
string[] values = new string[all.Count];
YesOutputBox.Text = " you got here";
foreach (Match m in all) //List all the words
{
values[index] = m.Value.Trim();
index++;
YesOutputBox.Text = YesOutputBox.Text + " " + m.Value;
}
for (int i = 0; i < removeWords.Length; i++)
{
removeWords[i] = new Regex(" " + values[i]);
// If the words appears more than one time
if (removeWords[i].Matches(test).Count > 1)
{
removeWords[i] = new Regex(" " + values[i] + " ");
test = removeWords[i].Replace(test, " "); //Remove the first word.
}
}
return test;
}

You can remove all occurences of "#sometext" from string test via the method
Regex.Replace(test, "#sometext", "")
or for any word starting with "#" you can use
Regex.Replace(test, "#\\w+", "")
If you need specifically a separate word (i.e. nothing like #comp within tom#comp.com) you may preceed the regex with a special word boundary (\b does not work here):
Regex.Replace(test, "(^|\\W)#\\w+", "")

You can use:
^\s#([A-Za-z0-9_]+)
as the regex to recognize Twitter usernames.

Regex to remove #something from this string: I want to remove #something from this string.
var regex = new Regex("#\\w*");
string result = regex.Replace(stringWithAt, "");
Is that what you are looking for?

I've had good luck applying this pattern:
\B#\w+
This will match any string starting with an # character that contains alphanumeric characters, plus some linking punctuation like the underscore character, if it does not occur on a boundary between alphanumeric and non-alphanumeric characters.
The result of executing this code:
string result = Regex.Replace(
#"#This1 #That2_thing this2#3that #the5Others #alpha#beta#gamma",
#"\B#\w+",
#"redacted");
is the following string:
redacted redacted this2#3that redacted redacted#beta#gamma
If this question is Twitter-specific, then Twitter provides an open source library that helps capture Twitter-specific entities like links, mentions and hashtags. This java file contains the code defining the regular expressions that Twitter uses, and this yml file contains test strings and expected outcomes of many unit tests that exercise the regular expressions in the Twitter library.
Twitter's mention-matching pattern (extracted from their library, modified to remove unnecessary capture groups, and edited to make sense in the context of a replacement) is shown below. The match should be performed in a case-insensitive manner.
(^|[^a-z0-9_])[#\uFF20][a-z0-9_]{1,20}
Here is an example which reproduces the results of the first replacement in my answer:
string result = Regex.Replace(
#"#This1 #That2_thing this2#3that #the5Others #alpha#beta#gamma",
#"(^|[^a-z0-9_])[#\uFF20][a-z0-9_]{1,20}",
#"$1redacted",
RegexOptions.IgnoreCase);
Note the need to include the substitution $1 since the first capture group can't be directly converted into an atomic zero-width assertion.