I have a problem to find the pattern that solves the problem in onestep.
The string looks like this:
Text1
Text1$Text2$Text3
Text1$Text2$Text3$Text4$Text5$Text6 etc.
What i want to get is: Take up to 4x Text. If there are more than "4xText" take only the last sign.
Example:
Text1$Text2$Text3$Text4$Text5$Text6 -> Text1$Text2$Text3$Text4&56
My current solution is:
First pattern:
^([^\$]*)\$?([^\$]*)\$?([^\$]*)\$?([^\$]*)\$?
After this i will do a substitution with the first pattern
New string: Text5$Text6
second pattern is:
([^\$])\b
result: 56
combine both and get the result:
Text1$Text2$Text3$Text4$56
For me it is not clear why i cant easily put the second pattern after the first pattern into one pattern. Is there something like an anchor that tells the engine to start the pattern from here like it would do if is would be the only pattern ?
You might use an alternation with a positive lookbehind and then concatenate the matches.
(?<=^(?:[^$]+\$){0,3})[^$]+\$?|[^$](?=\$|$)
Explanation
(?<= Positive lookbehind, assert what is on the left is
^(?:[^$]+\$){0,3} Match 0-3 times any char except $ followed by an optional $
) Close lookbehind
[^$]+\$? Match 1+ times any char except $, then match an optional $
| Or
[^$] Match any char except $
(?=\$|$) Positive lookahead, assert what is directly to the right is either $ or the end of the string
.NET regex demo | C# demo
Example
string pattern = #"(?<=^(?:[^$]*\$){0,3})[^$]*\$?|[^$](?=\$|$)";
string[] strings = {
"Text1",
"Text1$Text2$Text3",
"Text1$Text2$Text3$Text4$Text5$Text6"
};
Regex regex = new Regex(pattern);
foreach (String s in strings) {
Console.WriteLine(string.Join("", from Match match in regex.Matches(s) select match.Value));
}
Output
Text1
Text1$Text2$Text3
Text1$Text2$Text3$Text4$56
I strongly believe regular expression isn't the way to do that. Mostly because of the readability.
You may consider using simple algorithm like this one to reach your goal:
using System;
public class Program
{
public static void Main()
{
var input = "Text1$Text2$Text3$Text4$Text5$Text6";
var parts = input.Split('$');
var result = "";
for(var i=0; i<parts.Length; i++){
result += (i <= 4 ? parts[i] + "$" : parts[i].Substring(4));
}
Console.WriteLine(result);
}
}
There are also linq alternatives :
using System;
using System.Linq;
public class Program
{
public static void Main()
{
var input = "Text1$Text2$Text3$Text4$Text5$Text6";
var parts = input.Split('$');
var first4 = parts.Take(4);
var remainings = parts.Skip(4);
var result2 = string.Join("$", first4) + "$" + string.Join("", remainings.Select( r=>r.Substring(4)));
Console.WriteLine(result2);
}
}
It has to be adjusted to the actual needs but the idea is there
Try this code:
var texts = new string[] {"Text1", "Text1$Text2$Text3", "Text1$Text2$Text3$Text4$Text5$Text6" };
var parsed = texts
.Select(s => Regex.Replace(s,
#"(Text\d{1,3}(?:\$Text\d{1,3}){0,3})((?:\$Text\d{1,3})*)",
(match) => match.Groups[1].Value +"$"+ match.Groups[2].Value.Replace("Text", "").Replace("$", "")
)).ToArray();
// parsed is now: string[3] { "Text1$", "Text1$Text2$Text3$", "Text1$Text2$Text3$Text4$56" }
Explanation:
solution uses regex pattern: (Text\d{1,3}(?:\$Text\d{1,3}){0,3})((?:\$Text\d{1,3})*)
(...) - first capturing group
(?:...) - non-capturing group
Text\d{1,3}(?:\$Text\d{1,3} - match Text literally, then match \d{1,3}, which is 1 up to three digits, \$ matches $ literally
Rest is just repetition of it. Basically, first group captures first four pieces, second group captures the rest, if any.
We also use MatchEvaluator here which is delegate type defined as:
public delegate string MatchEvaluator(Match match);
We define such method:
(match) => match.Groups[1].Value +"$"+ match.Groups[2].Value.Replace("Text", "").Replace("$", "")
We use it to evaluate match, so takee first capturing group and concatenate with second, removing unnecessary text.
It's not clear to me whether your goal can be achieved using exclusively regex. If nothing else, the fact that you want to introduce a new character '&' into the output adds to the challenge, since just plain matching would never be able to accomplish that. Possibly using the Replace() method? I'm not sure that would work though...using only a replacement pattern and not a MatchEvaluator, I don't see a way to recognize but still exclude the "$Text" portion from the fifth instance and later.
But, if you are willing to mix regex with a small amount of post-processing, you can definitely do it:
static readonly Regex regex1 = new Regex(#"(Text\d(?:\$Text\d){0,3})(?:\$Text(\d))*", RegexOptions.Compiled);
static void Main(string[] args)
{
for (int i = 1; i <= 6; i++)
{
string text = string.Join("$", Enumerable.Range(1, i).Select(j => $"Text{j}"));
WriteLine(KeepFour(text));
}
}
private static string KeepFour(string text)
{
Match match = regex1.Match(text);
if (!match.Success)
{
return "[NO MATCH]";
}
StringBuilder result = new StringBuilder();
result.Append(match.Groups[1].Value);
if (match.Groups[2].Captures.Count > 0)
{
result.Append("&");
// Have to iterate (join), because we don't want the whole match,
// just the captured text.
result.Append(JoinCaptures(match.Groups[2]));
}
return result.ToString();
}
private static string JoinCaptures(Group group)
{
return string.Join("", group.Captures.Cast<Capture>().Select(c => c.Value));
}
The above breaks your requirement into three different capture groups in a regex. Then it extracts the captured text, composing the result based on the results.
Related
I want to select word2 from the following :
word2;word3
word2 that is between ; and start of the line unless there is a = in between. In that case, I want start from the = instead of the start of the line
like word2 from
word1=word2;word3
I have tried using this regex
(?<=\=|^).*?(?=;)
which select the word2 from
word2;word3
but also the whole word1=word2 from
word1=word2;word3
You can use an optional group to check for a word followed by an equals sign and capture the value in the first capturing group:
^(?:\w+=)?(\w+);
Explanation
^ Start of string
(?:\w+=)? Optional non capturing group matching 1+ word chars followed by =
(\w+) Capture in the first capturing group 1+ word chars
; Match ;
See a regex demo
In .NET you might also use:
(?<=^(?:\w+=)?)\w+(?=;)
Regex demo | C# demo
There should be so many options, maybe regular expressions among the last ones.
But, if we wish to use an expression for this problem, let's start with a simple one and explore other options, maybe something similar to:
(.+=)?(.+?);
or
(.+=)?(.+?)(?:;.+)
where the second capturing group has our desired word2.
Demo 1
Demo 2
Example 1
using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = #"(.+=)?(.+?);";
string input = #"word1=word2;word3
word2;word3";
RegexOptions options = RegexOptions.Multiline;
foreach (Match m in Regex.Matches(input, pattern, options))
{
Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);
}
}
}
Example 2
using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = #"(.+=)?(.+?)(?:;.+)";
string substitution = #"$2";
string input = #"word1=word2;word3
word2;word3";
RegexOptions options = RegexOptions.Multiline;
Regex regex = new Regex(pattern, options);
string result = regex.Replace(input, substitution);
}
}
Instead of using regular expresions you can solve the problem with String class methods.
string[] words = str.Split(';');
string word2 = words[0].Substring(words[0].IndexOf('=') + 1);
First line splits the line from ';'. Assuming you just have a single ';' this statement splits your line into two strings. And second line returns a substring of first part (words[0]) starting from the first occurence of '=' (words[0].IndexOf('=')) character's next characher (+1) to the end. If your line doesn't have any '=' characters it just starts from the beginning because IndexOf returns -1.
Related documentation:
https://learn.microsoft.com/en-us/dotnet/api/system.string.split?view=netframework-4.8
https://learn.microsoft.com/en-us/dotnet/api/system.string.substring?view=netframework-4.8
https://learn.microsoft.com/en-us/dotnet/api/system.string.indexof?view=netframework-4.8
I am trying to get the regex to match only when there is one letter from A-Z followed by a = like this A=, a=, B=, currently it is picking up any number of letters before the = like hem=, ac2=. Usually ^[a-zA-Z] works just fine but its not working for this case since I'm using named capture groups
String pattern = "FL2 (77) Flashing,77,a=1.875,A=90.0,b=3.625,B=95.0,c=1.375,C=175.0,d=2.5,hem=0.5,16GA-AL,";
var regex = new Regex("(?<label>[a-zA-Z]+)=(?<value>[^,]+)");
Other ways I've tried
var regex = new Regex("(?<label>^[a-zA-Z]+)=(?<value>[^,]+)");
var regex = new Regex("(?<label>[^a-zA-Z]+)=(?<value>[^,]+)");
If you want to match l= but not word=, you need a negative look-behind assertion.
new Regex("(?<![a-zA-Z])(?<label>[a-zA-Z])=(?<value>[^,]+)")
If the string pattern you have in your question is really the "haystack" in which you're looking for "needles", a really easy way to solve the problem would be to first split the string on ,, then use RegEx. Then you can use a simpler pattern ^(?<label>[a-zA-Z])=(?<value>.+)$ on each item in the list you get from splitting the string, and only keep the matches.
It's because you have a + after [a-zA-Z], which makes it match one or more characters in that character class. If you remove the +, it will only match one character before the =.
If you want it to only match in situations where there is exactly one alphabetical character before the equals sign, you will want to add to the beginning of the regex to make sure that the character before the letter you want to match is not a letter, like this:
(?<![a-zA-Z])(?<label>[a-zA-Z])=(?<value>[^,]+)
(notice though that this only matters in the case where you don't put a ^ before [a-zA-Z], in the case where you want matches that don't start at the beginning of a line)
Have you tried
var regex = new Regex("(?<label>^[a-zA-Z]?)=(?<value>[^,]+)");
I believe the "+" means 1 or more
"?" means 0 or 1
or exactly 1 should be {1} (at least in python, not sure about C#)
var regex = new Regex("(?<label>^[a-zA-Z]{1})=(?<value>[^,]+)");
Assuming that the label is separated by a comma (which seems to be the case based on your example and code) then you can use:
^|,(?<label>[A-Za-z])=(?<value>[^,]+)
I recommend Regex.Matches over capture groups here:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
namespace Rextester
{
public class Program
{
public static void Main(string[] args)
{
string content = "FL2 (77) Flashing,77,a=1.875,A=90.0,b=3.625,B=95.0,c=1.375,C=175.0,d=2.5,hem=0.5,16GA-AL,";
const string regexPattern = "(?<=[,| ])[a-zA-Z]=([0-9|.|-])+";
string singleMatch = new Regex(regexPattern).Match(content).ToString();
Console.WriteLine(singleMatch); // a=1.875
MatchCollection matchList = Regex.Matches(content, regexPattern);
var matches = matchList.Cast<Match>().Select(match => match.Value).ToList();
Console.WriteLine(string.Join(", ", matches)); // a=1.875, A=90.0, b=3.625, B=95.0, c=1.375, C=175.0, d=2.5
}
}
}
I would like to use the ((?!(SEPARATOR)).)* regex pattern for splitting a string.
using System;
using System.Text.RegularExpressions;
public class Program
{
public static void Main()
{
var separator = "__";
var pattern = String.Format("((?!{0}).)*", separator);
var regex = new Regex(pattern);
foreach (var item in regex.Matches("first__second"))
Console.WriteLine(item);
}
}
It works fine when a SEPARATOR is a single character, but when it is longer then 1 character I get an unexpected result. In the code above the second matched string is "_second" instead of "second". How shall I modify my pattern to skip the whole unmatched separator?
My real problem is to split lines where I should skip line separators inside quotes. My line separator is not a predefined value and it can be for example "\r\n".
You can do something like this:
using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string input = "plum--pear";
string pattern = "-"; // Split on hyphens
string[] substrings = Regex.Split(input, pattern);
foreach (string match in substrings)
{
Console.WriteLine("'{0}'", match);
}
}
}
// The method displays the following output:
// 'plum'
// ''
// 'pear'
The .NET regex does not does not support matching a piece of text other than a specific multicharacter string. In PCRE, you would use (*SKIP)(*FAIL) verbs, but they are not supported in the native .NET regex library. Surely, you might want to use PCRE.NET, but .NET regex can usually handle those scenarios well with Regex.Split
If you need to, say, match all but [anything here], you could use
var res = Regex.Split(s, #"\[[^][]*]").Where(m => !string.IsNullOrEmpty(m));
If the separator is a simple literal fixed string like __, just use String.Split.
As for your real problem, it seems all you need is
var res = Regex.Matches(s, "(?:\"[^\"]*\"|[^\r\n\"])+")
.Cast<Match>()
.Select(m => m.Value)
.ToList();
See the regex demo
It matches 1+ (due to the final +) occurrences of ", 0+ chars other than " and then " (the "[^"]*" branch) or (|) any char but CR, LF or/and " (see [^\r\n"]).
Assuming I have this input:
/green/blah/agriculture/apple/blah/
I'm only trying to capture and replace the occurrence of apple (need to replace it with orange), so I have this regex
var regex = new Regex("^/(?:green|red){1}(?:/.*)+(apple){1}(?:/.*)");
So I'm grouping sections of the input, but as non-capturing, and only capturing the one I'm concerned with. According to this $` will retrieve everything before the match in the input string, and $' will get everything after, so theoretically the following should work:
"$`Orange$'"
But it only retrieves the match ("apple").
Is it possible to do this with just substitutions and NOT match evaluators and looping through groups?
The issue is that apple can occur anywhere in that url scheme, hence an unknown number of capture groups.
Thanks.
To achieve what you want, I slightly changed your regex.
The new regex looks like this look for the updated version at the end of the answer:
What I am doing here is, I want all the other groups to become captured groups. Doing this I can use them as follow:
String replacement = "$1Orange$2";
string result = Regex.Replace(text, regex.ToString(), replacement);
I am using group 1,2 and 4 and in the middle of everything (where I suspect 'apple') I replace it with Orange.
A complete example looks like this:
using System;
using System.Text.RegularExpressions;
public class Test
{
public static void Main()
{
String text = "/green/blah/agriculture/apple/blah/hallo/apple";
var regex = new Regex("^(/(?:green|red)/(?:[^/]+/)*?)apple(/.*)");
String replacement = "$1$2Orange$4";
string result = Regex.Replace(text, regex.ToString(), replacement);
Console.WriteLine(result);
}
}
And as well a running example is here
See the updated regex, I needed to change it again to capture things like this:
/green/blah/agriculture/apple/blah/hallo/apple/green/blah/agriculture/apple/blah/hallo/apple
With the above regex it matched the last apple and not the first as prio designated. I changed the regex to this:
var regex = new Regex("^(/(?:green|red)/(?:[^/]+/)*?)apple(/.*)");
I updated the code as well as the running example.
If you really want to replace only the first occurence of apple and dont mind about the URL structure then can you use one of the following methods:
First simply use apple as regex and use the overloaded Replace method.
using System;
using System.Text.RegularExpressions;
public class Test
{
public static void Main()
{
String text = "/green/blah/agriculture/apple/blah/hallo/apple/green/blah/agriculture/apple/blah/hallo/apple";
var regex = new Regex(Regex.Escape("apple"));
String replacement = "Orange";
string result = regex.Replace(text, replacement.ToString(), 1);
Console.WriteLine(result);
}
}
See working Example
Second is the use of IndexOf and Substring which could be much quick as the use of the regex classes.
See the following Example:
class Program
{
static void Main(string[] args)
{
string search = "apple";
string text = "/green/blah/agriculture/apple/blah/hallo/apple/green/blah/agriculture/apple/blah/hallo/apple";
int idx = text.IndexOf(search);
int endIdx = idx + search.Length;
int secondStrLen = text.Length - endIdx;
if (idx != -1 && idx < text.Length && endIdx < text.Length && secondStrLen > -1)
{
string first = text.Substring(0, idx);
string second = text.Substring(endIdx, secondStrLen);
string result = first + "Orange" + second;
Console.WriteLine(result);
}
}
}
Working Example
Consider two regular expressions:
var regex_A = "Main\.(.+)\.Value";
var regex_B = "M_(.+)_Sp";
I want to be able to replace a string using regex_A as input, and regex_B as the replacement string. But also the other way around. And without supplying additional information like a format string per regex.
Specifically I want to create a replaced_B string from an input_A string. So:
var input_A = "Main.Rotating.Value";
var replaced_B = input_A.RegEx_Awesome_Replace(regex_A, regex_B);
Assert.AreEqual("M_Rotating_Sp", replaced_B);
And this should also work in reverse (thats the reason i can't use a simple string.format for regex_B). Because I don't want to supply a format string for every regular expression (i'm lazy).
var input_B = "M_Skew_Sp";
var replaced_A = input_B.RegEx_Awesome_Replace(regex_B, regex_A);
Assert.AreEqual("Main.Skew.Value", replaced_A);
I have no clue if this exists, or how to call it. Google search finds me all kinds of other regex replaces... not this one.
Update:
So basically I need a way to convert a regular expression to a format string.
var regex_A_format = Regex2Format(regex_A);
Assert.AreEqual("Main.$1.Value", regex_A_format);
and
var regex_B_format = Regex2Format(regex_B);
Assert.AreEqual("M_$1_Sp", regex_B_format);
So what should the RegEx_Awesome_Replace and/or Regex2Format function look like?
Update 2:
I guess the RegEx_Awesome_Replace should look something like (using some code from answers below):
public static class StringExtenstions
{
public static string RegExAwesomeReplace(this string inputString,string searchPattern,string replacePattern)
{
return Regex.Replace(inputString, searchPattern, Regex2Format(replacePattern));
}
}
Which would leave the Regex2Format as an open question.
There is no defined way for one regex to refer to a match found in another regex. Regexes are not format strings.
What you can do is to use Tuples of a format string together with its regex. e.g.
var a = new Tuple<Regex,string>(new Regex(#"(?<=Main\.).+(?=\.Value)"), #"Main.{0}.Value")
var b = new Tuple<Regex,string>(new Regex(#"(?<=M_).+(?=_Sp)"), #"M_{0}_Sp")`
Then you can pass these objects to a common replacement method in any order, like this:
private string RegEx_Awesome_Replace(string input, Tuple<Regex,string> toFind, Tuple<Regex,string> replaceWith)
{
return string.Format(replaceWith.Item2, toFind.Item1.Match(input).Value);
}
You will notice that I have used zero-width positive lookahead assertion and zero-width positive lookbehind assertions in my regexes, to ensure that Value contains exactly the text that I want to replace.
You may also want to add error handling, for cases where the match can not be found. Maybe read about Regex.Match
Since you have already reduced your problem to where you need to change a Regex into a string format (implementing Regex2Format) I will focus my answer just on that part. Note that my answer is incomplete because it doesn't address the full breadth of parsing regex capturing groups, however it works for simple cases.
First thing needed is a Regex that will match Regex capture groups. There is a negative lookbehind to not match escaped bracket symbols. There are other cases that break this regex. E.g. a non-capturing group, wildcard symbols, things between square braces.
private static readonly Regex CaptureGroupMatcher = new Regex(#"(?<!\\)\([^\)]+\)");
The implementation of Regex2Format here basically writes everything outside of capture groups into the output string, and replaces the capture group value by {x}.
static string Regex2Format(string pattern)
{
var targetBuilder = new StringBuilder();
int previousEndIndex = 0;
int formatIndex = 0;
foreach (Match match in CaptureGroupMatcher.Matches(pattern))
{
var group = match.Groups[0];
int endIndex = group.Index;
AppendPart(pattern, previousEndIndex, endIndex, targetBuilder);
targetBuilder.Append('{');
targetBuilder.Append(formatIndex++);
targetBuilder.Append('}');
previousEndIndex = group.Index + group.Length;
}
AppendPart(pattern, previousEndIndex, pattern.Length, targetBuilder);
return targetBuilder.ToString();
}
This helper function writes pattern string values into the output, it currently writes everything except \ characters used to escape something.
static void AppendPart(string pattern, int previousEndIndex, int endIndex, StringBuilder targetBuilder)
{
for (int i = previousEndIndex; i < endIndex; i++)
{
char c = pattern[i];
if (c == '\\' && i < pattern.Length - 1 && pattern[i + 1] != '\\')
{
//backslash not followed by another backslash - it's an escape char
}
else
{
targetBuilder.Append(c);
}
}
}
Test cases
static void Test()
{
var cases = new Dictionary<string, string>
{
{ #"Main\.(.+)\.Value", #"Main.{0}.Value" },
{ #"M_(.+)_Sp(.*)", "M_{0}_Sp{1}" },
{ #"M_\(.+)_Sp", #"M_(.+)_Sp" },
};
foreach (var kvp in cases)
{
if (PatternToStringFormat(kvp.Key) != kvp.Value)
{
Console.WriteLine("Test failed for {0} - expected {1} but got {2}", kvp.Key, kvp.Value, PatternToStringFormat(kvp.Key));
}
}
}
To wrap up, here is the usage:
private static string AwesomeRegexReplace(string input, string sourcePattern, string targetPattern)
{
var targetFormat = PatternToStringFormat(targetPattern);
return Regex.Replace(input, sourcePattern, match =>
{
var args = match.Groups.OfType<Group>().Skip(1).Select(g => g.Value).ToArray<object>();
return string.Format(targetFormat, args);
});
}
Something like this might work
var replaced_B = Regex.Replace(input_A, #"Main\.(.+)\.Value", #"M_$1_Sp");
Are you looking for something like this?
public static class StringExtenstions
{
public static string RegExAwesomeReplace(this string inputString,string searchPattern,string replacePattern)
{
Match searchMatch = Regex.Match(inputString,searchPattern);
Match replaceMatch = Regex.Match(inputString, replacePattern);
if (!searchMatch.Success || !replaceMatch.Success)
{
return inputString;
}
return inputString.Replace(searchMatch.Value, replaceMatch.Value);
}
}
The string extension method returns the string with replaced value for search pattern and replace pattern.
This is how you call:
input_A.RegEx_Awesome_Replace(regex_A, regex_B);