I have the following Regex:
[A-Z]{2}[0-9]{4}
and it matches perfectly with a string like this: AB1234. But I have to improve this Regex to match with these specific rules:
The string must have only two sharps (##) between each group (AB1234##AB1234)
It may have 8 groups of string (AB1234##AB1234##AB1234##AB1234##AB1234##AB1234##AB1234##AB1234)
Regardless the number of groups, the last one cannot have the sharps (##) at the end. So, if I have 3 groups, it will looks like this: AB1234##AB1234##AB1234
If I use the sample string from the second bullet point, my Regex will match with the pattern, but in this case it doesn't validade the characters between each group.
Can anyone help me to improve this Regex?
Try this:
^([A-Z]{2}[0-9]{4}##){0,7}([A-Z]{2}[0-9]{4})$
([A-Z]{2}[0-9]{4}##){0,7}([A-Z]{2}[0-9]{4})
You can combine Regex and LINQ then use an extension method like this:
public static bool Validate(this string source)
{
string pattern = "[A-Z]{2}[0-9]{4}";
return !source.StartsWith("##") &&
!source.EndsWith("##") &&
source.Split(new[] {"##"}, StringSplitOptions.RemoveEmptyEntries)
.All(x => Regex.IsMatch(x, pattern));
}
Usage:
bool t1 = "AB1234##AB1234".Validate(); // true
bool t2 = "AB1234##AB1234##AB1234".Validate(); // true
bool t3 = "AB1234##AB1234##" // false
^(?:[A-Z]{2}[0-9]{4})(?:##(?:[A-Z]{2}[0-9]{4})){0,7}$
^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^ ^^^
(1) (2) (3)
Match at least one string that begins with two capital letters that is followed by 4 decimal digits.
Optionally follow that from zero to 7 times by ## and a repetition of the first match.
Result: (* indicates a match)
* AB1234
AB1234x
* AB1234##AB1234
* AB1234##AB1234##AB1234
AB1234##AB1234##AB1234x
See the live demo.
Note: This answer is quite similar to this other answer. However, the answer here begins with the assumption that at least one sequence of AB1234 is present. And it then allows for the possibility that it is followed zero to 7 times by ##AB1234. In the end, both regex expressions are fine. It comes down to personal preference.
Also note that I used non-capturing groups (?:...) to avoid the unnecessary overhead of creating capture groups that aren't needed in this situation. (Capture groups are also known as back-references.)
Related
In C# I'm trying to validate a string that looks like:
I#paramname='test'
or
O#paramname=2827
Here is my code:
string t1 = "I#parameter='test'";
string r = #"^([Ii]|[Oo])#\w=\w";
var re = new Regex(r);
If I take the "=\w" off the end or variable r I get True. If I add an "=\w" after the \w it's False. I want the characters between # and = to be able to be any alphanumeric value. Anything after the = sign can have alphanumeric and ' (single quotes). What am I doing wrong here. I very rarely have used regular expressions and normally can find example, this is custom format though and even with cheatsheets I'm having issues.
^([Ii]|[Oo])#\w+=(?<q>'?)[\w\d]+\k<q>$
Regular expression:
^ start of line
([Ii]|[Oo]) either (I or i) or (O or o)
\w+ 1 or more word characters
= equals sign
(?<q>'?) capture 0 or 1 quotes in named group q
[\w\d]+ 1 or more word or digit characters
\k<q> repeat of what was captured in named group q
$ end of line
use \w+ instead of \w to one character or more. Or \w* to get zero or more:
Try this: Live demo
^([Ii]|[Oo])#\w+=\'*\w+\'*
If you are being a bit more strict with using paramname:
^([Ii]|[Oo])#paramname=[']?[\w]+[']?
Here is a demo
You could try something like this:
Regex rx = new Regex( #"^([IO])#(\w+)=(.*)$" , RegexOptions.IgnoreCase ) ;
Match group 1 will give you the value of I or O (the parameter direction?)
Match group 2 will give you the name of the parameter
Match group 3 will give you the value of the parameter
You could be stricter about the 3rd group and match it as
(([^']+)|('(('')|([^']+))*'))
The first alternative matches 1 or more non quoted character; the second alternative match a quoted string literal with any internal (embedded) quotes escape by doubling them, so it would match things like
'' (the empty string
'foo bar'
'That''s All, Folks!'
Suppose I have a string
Likes (20)
I want to fetch the sub-string enclosed in round brackets (in above case its 20) from this string. This sub-string can change dynamically at runtime. It might be any other number from 0 to infinity. To achieve this my idea is to use a for loop that traverses the whole string and then when a ( is present, it starts adding the characters to another character array and when ) is encountered, it stops adding the characters and returns the array. But I think this might have poor performance. I know very little about regular expressions, so is there a regular expression solution available or any function that can do that in an efficient way?
If you don't fancy using regex you could use Split:
string foo = "Likes (20)";
string[] arr = foo.Split(new char[]{ '(', ')' }, StringSplitOptions.None);
string count = arr[1];
Count = 20
This will work fine regardless of the number in the brackets ()
e.g:
Likes (242535345)
Will give:
242535345
Works also with pure string methods:
string result = "Likes (20)";
int index = result.IndexOf('(');
if (index >= 0)
{
result = result.Substring(index + 1); // take part behind (
index = result.IndexOf(')');
if (index >= 0)
result = result.Remove(index); // remove part from )
}
Demo
For a strict matching, you can do:
Regex reg = new Regex(#"^Likes\((\d+)\)$");
Match m = reg.Match(yourstring);
this way you'll have all you need in m.Groups[1].Value.
As suggested from I4V, assuming you have only that sequence of digits in the whole string, as in your example, you can use the simpler version:
var res = Regex.Match(str,#"\d+")
and in this canse, you can get the value you are looking for with res.Value
EDIT
In case the value enclosed in brackets is not just numbers, you can just change the \d with something like [\w\d\s] if you want to allow in there alphabetic characters, digits and spaces.
Even with Linq:
var s = "Likes (20)";
var s1 = new string(s.SkipWhile(x => x != '(').Skip(1).TakeWhile(x => x != ')').ToArray());
const string likes = "Likes (20)";
int likesCount = int.Parse(likes.Substring(likes.IndexOf('(') + 1, (likes.Length - likes.IndexOf(')') + 1 )));
Matching when the part in paranthesis is supposed to be a number;
string inputstring="Likes (20)"
Regex reg=new Regex(#"\((\d+)\)")
string num= reg.Match(inputstring).Groups[1].Value
Explanation:
By definition regexp matches a substring, so unless you indicate otherwise the string you are looking for can occur at any place in your string.
\d stand for digits. It will match any single digit.
We want it to potentially be repeated several times, and we want at least one. The + sign is regexp for previous symbol or group repeated 1 or more times.
So \d+ will match one or more digits. It will match 20.
To insure that we get the number that is in paranteses we say that it should be between ( and ). These are special characters in regexp so we need to escape them.
(\d+) would match (20), and we are almost there.
Since we want the part inside the parantheses, and not including the parantheses we tell regexp that the digits part is a single group.
We do that by using parantheses in our regexp. ((\d+)) will still match (20), but now it will note that 20 is a subgroup of this match and we can fetch it by Match.Groups[].
For any string in parantheses things gets a little bit harder.
Regex reg=new Regex(#"\((.+)\)")
Would work for many strings. (the dot matches any character) But if the input is something like "This is an example(parantesis1)(parantesis2)", you would match (parantesis1)(parantesis2) with parantesis1)(parantesis2 as the captured subgroup. This is unlikely to be what you are after.
The solution can be to do the matching for "any character exept a closing paranthesis"
Regex reg=new Regex(#"\(([^\(]+)\)")
This will find (parantesis1) as the first match, with parantesis1 as .Groups[1].
It will still fail for nested paranthesis, but since regular expressions are not the correct tool for nested paranthesis I feel that this case is a bit out of scope.
If you know that the string always starts with "Likes " before the group then Saves solution is better.
I can't understand how to solve the following problem:
I have input string "aaaabaa" and I'm trying to search for string "aa" (I'm looking for positions of characters)
Expected result is
0 1 2 5
aa aabaa
a aa abaa
aa aa baa
aaaab aa
This problem is already solved by me using another approach (non-RegEx).
But I need a RegEx I'm new to RegEx so google-search can't help me really.
Any help appreciated! Thanks!
P.S.
I've tried to use (aa)* and "\b(\w+(aa))*\w+" but those expressions are wrong
You can solve this by using a lookahead
a(?=a)
will find every "a" that is followed by another "a".
If you want to do this more generally
(\p{L})(?=\1)
This will find every character that is followed by the same character. Every found letter is stored in a capturing group (because of the brackets around), this capturing group is then reused by the positive lookahead assertion (the (?=...)) by using \1 (in \1 there is the matches character stored)
\p{L} is a unicode code point with the category "letter"
Code
String text = "aaaabaa";
Regex reg = new Regex(#"(\p{L})(?=\1)");
MatchCollection result = reg.Matches(text);
foreach (Match item in result) {
Console.WriteLine(item.Index);
}
Output
0
1
2
5
The following code should work with any regular expression without having to change the actual expression:
Regex rx = new Regex("(a)\1"); // or any other word you're looking for.
int position = 0;
string text = "aaaaabbbbccccaaa";
int textLength = text.Length;
Match m = rx.Match(text, position);
while (m != null && m.Success)
{
Console.WriteLine(m.Index);
if (m.Index <= textLength)
{
m = rx.Match(text, m.Index + 1);
}
else
{
m = null;
}
}
Console.ReadKey();
It uses the option to change the start index of a regex search for each consecutive search. The actual problem comes from the fact that the Regex engine, by default, will always continue searching after the previous match. So it will never find a possible match within another match, unless you instruct it to by using a Look ahead construction or by manually setting the start index.
Another, relatively easy, solution is to just stick the whole expression in a forward look ahead:
string expression = "(a)\1"
Regex rx2 = new Regex("(?=" + expression + ")");
MatchCollection ms = rx2.Matches(text);
var indexes = ms.Cast<Match>().Select(match => match.Index);
That way the engine will automatically advance the index by one for every match it finds.
From the docs:
When a match attempt is repeated by calling the NextMatch method, the regular expression engine gives empty matches special treatment. Usually, NextMatch begins the search for the next match exactly where the previous match left off. However, after an empty match, the NextMatch method advances by one character before trying the next match. This behavior guarantees that the regular expression engine will progress through the string. Otherwise, because an empty match does not result in any forward movement, the next match would start in exactly the same place as the previous match, and it would match the same empty string repeatedly.
Try this:
How can I find repeated characters with a regex in Java?
It is in java, but the regex and non-regex way is there. C# Regex is very similar to the Java way.
Is it possible to write a regular expression to check whether all numbers of specific 10 digit number occured up to 3 times?
for example return value for Regex.IsMatch("xxxx", "4433425425") is false.
and for Regex.IsMatch("xxxx", "4463322545") is true. what is xxxx?
in the first one i have 4 occurrence of digit 4 and in second one non of digits occurred more than 3 times.
Will match any digit that has four or more instances
string found = Regex.Match(s,#"(\d).*\1.*\1.*\1").Groups[1].Value;
Just an example of how to use it
static void Main( string[] args )
{
string fail = "1234567890";
string s = "1231231222";
string mTxt = #"(\d).*\1.*\1.*\1";
Console.WriteLine( Regex.Match(s,mTxt).Success);
Console.WriteLine(Regex.Match(fail, mTxt).Success);
}
Baised on #Brads Comments below use
([0-9]).*\1.*\1.*\1
Find a number occurring three times in a row:
(?=(0{3}|1{3}|2{3}|3{3}|4{3}|5{3}|6{3}|7{3}|8{3}|9{3}).{3}
Find a number occurring three times anywhere in the string:
(.?0.?){3}|(.?1.?){3}|(.?2.?){3}|(.?3.?){3}|(.?4.?){3}|(.?5.?){3}|(.?6.?){3}|(.?7.?){3}|(.?8.?){3}|(.?9.?){3}
Using backreferences (C/O #rerun):
([0-9]).*\1.*\1.*
NOTE: this will check the entire string for multiple characters. There is no limitation to the first 10 characters in the string. Let me know if you need that.
I'm going to risk downvotes here and suggest that regexes are most likely not the best tool for this job.
They have their place but I usually find that, if you're getting into "horrendous" territory with multiple backtracking or negative lookahead and lots of or clauses, you're probably better off tossing away the whole regex idea and writing a simple string scanning function which simply count each digit and ensures the counts are correct at the end. Pseudo-code something like:
def isValid (str):
foreach ch in '0'..'9':
count[ch] = 0
foreach ch in str:
if ch not in '0'..'9':
return false
count[ch] = count[ch] + 1
foreach ch in '0'..'9':
if count[ch] > 3:
return false
return true
That's my advice, take it or leave it, I won't be offended :-)
I have a string which has several html comments in it. I need to count the unique matches of an expression.
For example, the string might be:
var teststring = "<!--X1-->Hi<!--X1-->there<!--X2-->";
I currently use this to get the matches:
var regex = new Regex("<!--X.-->");
var matches = regex.Matches(teststring);
The results of this is 3 matches. However, I would like to have this be only 2 matches since there are only two unique matches.
I know I can probably loop through the resulting MatchCollection and remove the extra Match, but I'm hoping there is a more elegant solution.
Clarification: The sample string is greatly simplified from what is actually being used. There can easily be an X8 or X9, and there are likely dozens of each in the string.
I would just use the Enumerable.Distinct Method for example like this:
string subjectString = "<!--X1-->Hi<!--X1-->there<!--X2--><!--X1-->Hi<!--X1-->there<!--X2-->";
var regex = new Regex(#"<!--X\d-->");
var matches = regex.Matches(subjectString);
var uniqueMatches = matches
.OfType<Match>()
.Select(m => m.Value)
.Distinct();
uniqueMatches.ToList().ForEach(Console.WriteLine);
Outputs this:
<!--X1-->
<!--X2-->
For regular expression, you could maybe use this one?
(<!--X\d-->)(?!.*\1.*)
Seems to work on your test string in RegexBuddy at least =)
// (<!--X\d-->)(?!.*\1.*)
//
// Options: dot matches newline
//
// Match the regular expression below and capture its match into backreference number 1 «(<!--X\d-->)»
// Match the characters “<!--X” literally «<!--X»
// Match a single digit 0..9 «\d»
// Match the characters “-->” literally «-->»
// Assert that it is impossible to match the regex below starting at this position (negative lookahead) «(?!.*\1.*)»
// Match any single character «.*»
// Between zero and unlimited times, as many times as possible, giving back as needed (greedy) «*»
// Match the same text as most recently matched by capturing group number 1 «\1»
// Match any single character «.*»
// Between zero and unlimited times, as many times as possible, giving back as needed (greedy) «*»
It appears you're doing two different things:
Matching comments like /<-- X. -->/
Finding the set of unique comments
So it is fairly logical to handle these as two different steps:
var regex = new Regex("<!--X.-->");
var matches = regex.Matches(teststring);
var uniqueMatches = matches.Cast<Match>().Distinct(new MatchComparer());
class MatchComparer : IEqualityComparer<Match>
{
public bool Equals(Match a, Match b)
{
return a.Value == b.Value;
}
public int GetHashCode(Match match)
{
return match.Value.GetHashCode();
}
}
Extract the comments and store them in an array. Then you can filter out the unique values.
But I don’t know how to implement this in C#.
Depending on how many Xn's you have you might be able to use:
(\<!--X1--\>){1}.*(\<!--X2--\>){1}
That will only match each occurrence of the X1, X2 etc. once provided they are in order.
Capture the inner portion of the comment as a group. Then put those strings into a hashtable(dictionary). Then ask the dictionary for its count, since it will self weed out repeats.
var teststring = "<!--X1-->Hi<!--X1-->there<!--X2-->";
var tokens = new Dicationary<string, string>();
Regex.Replace(teststring, #"<!--(.*)-->",
match => {
tokens[match.Groups[1].Value] = match.Groups[1].Valuel;
return "";
});
var uniques = tokens.Keys.Count;
By using the Regex.Replace construct you get to have a lambda called on each match. Since you are not interested in the replace, you don't set it equal to anything.
You must use Group[1] because group[0] is the entire match.
I'm only repeating the same thing on both sides, so that its easier to put into the dictionary, which only stores unique keys.
If you want a distinct Match list from a MatchCollection without converting to string, you can use something like this:
var distinctMatches = matchList.OfType<Match>().GroupBy(x => x.Value).Select(x =>x.First()).ToList();
I know it has been 12 years but sometimes we need this kind of solutions, so I wanted to share. C# evolved, .NET evolved, so it's easier now.