Develop Reference

Replace floating numbers in math equation with letter variables

I want to replace all the floating numbers from a mathematical expression with letters using regular expressions. This is what I've tried:
Regex rx = new Regex("[-]?([0-9]*[.])?[0-9]+");
string expression = "((-30+5.2)*(2+7))-((-3.1*2.5)-9.12)";
char letter = 'a';
while (rx.IsMatch(expression))
{
expression = rx.Replace(expression , letter.ToString(), 1);
letter++;
}
The problem is that if I have for example (5-2)+3 it will replace it to: (ab)+c
So it gets the -2 as a number but I don't want that.
I am not experienced with Regex but I think I need something like this:
Check for '-', if there is a one, check if there is a number or right parenthesis before it. If there is NOT then save the '-'.
After that check for digits + dot + digits
My above Regex also works with values like: .2 .3 .4 but I don't need that, it should be explicit: 0.2 0.3 0.4

Following the suggested logic, you may consider
(?:(?<![)0-9])-)?[0-9]+(?:\.[0-9]+)?
See the regex demo.
Regex details
(?:(?<![)0-9])-)? - an optional non-capturing group matching 1 or 0 occurrences of
(?<![)0-9]) - a place in string that is not immediately preceded with a ) or digit
- - a minus
[0-9]+ - 1+ digits
(?:\.[0-9]+)? - an optional non-capturing group matching 1 or 0 occurrences of a . followed with 1+ digits.
In code, it is better to use a match evaluator (see the C# demo online):
Regex rx = new Regex(#"(?:(?<![)0-9])-)?[0-9]+(?:\.[0-9]+)?");
string expression = "((-30+5.2)*(2+7))-((-3.1*2.5)-9.12)";
char letter = (char)96; // char before a in ASCII table
string result = rx.Replace(expression, m =>
{
letter++; // char is incremented
return letter.ToString();
}
);
Console.WriteLine(result); // => ((a+b)*(c+d))-((e*f)-g)

Regex C# Matching string from two words in exact order and returning capture of non-matched words

C# Regex
I have the following list of strings:
"New patient, brief"
"New patient, limited"
"Established patient, brief"
"Established patient, limited"
"New diet patient"
"Established diet patient"
"School Physical"
"Deposition, 1 hour"
"Deposition, 2 hour"
I would like to separate these strings into groups using regex.
The first pattern I see is:
"New" or "Established" -- will be the first word of the matched pattern. This word will need to be captured and returned. Of this pattern, "patient" must be present without need to capture. Any word after "patient" must be captured.
I've tried: ((?=.*\bNew\b))(?=.*\bpatient\b)([A-Za-z0-9\-]+)
but the return match gives:
Full match 0-3 `New`
Group 1. 0-0 ``
Group 2. 0-3 `New`
Not at all what I am looking for.
string input = "New patient, limited";
string pattern = #"((?=.*\bNew\b))(?=.*\bpatient\b)([A-Za-z0-9\-]+)";
MatchCollection matches = Regex.Matches(input, pattern);
GroupCollection groups = matches[0].Groups;
foreach (Match match in matches)
{
Console.WriteLine("First word: {0}", match.Groups[1].Value);
Console.WriteLine("Last words: {0}", match.Groups[2].Value);
Console.WriteLine();
}
Console.WriteLine();
Thank you for any help with this.
Edit #1
For strings like "New patient, limited"
output should be: "New" "limited"
For strings like "Deposition, 1 hour" where "hour" is present,
output should be: "Deposition, 1 hour"
For strings where there are no words after "patient" but "patient" is present, like
"New diet patient",
output should be: "New" "diet"
For strings where neither "patient" nor "hour" is present, the entire string should be returned. i.e like "School Physical" should return the entire string,
"School Physical".
As I said, this is my ultimate quest. At the moment, I am trying to focus on separating out only the first pattern :). Much Thanks.

I suggest using
^(?:(?!\b(?:New|Established)\b).)*$|\b(New|Established)\s+(?:patient\b\W*)?(.+)
See the regex demo
Details
^(?:(?!\b(?:New|Established)\b).)*$ - any string that has no New or Established as whole words
| - or
\b(New|Established) - a whole word New or Established (put into Group 1)
\s+ - 1+ whitespaces
(?:patient\b\W*)? - an optional non-capturing group matching 1 or 0 occurrences of patient followed with word boundary and 0+ non-word chars
(.+) - Group 2: any 1 or more chars other than line break chars.
The code will look like
var match = Regex.Match(s, #"^(?:(?!\b(?:New|Established)\b).)*$|\b(New|Established)\s+(?:patient\b\W*)?(.+)");
If Group 1 is not matched (!match.Groups[1].Success), grab the whole match, match.Value. Else, grab match.Groups[1].Value and match.Groups[2].Value.
Results:

Regex - Trying to write match validation for Swedish Social Number

So I want the formats xxxxxx-xxxx AND xxxxxxxx-xxxx to be possible. I've managed to fix the first section before the dash, but the last four digits are troublesome. It does require to match at least 4 characters, but I also want the regex to return false if there's more than 4 characters. How do I do it?
This is how it looks so far:
var regex = new Regex(#"^\d{6,8}[-|(\s)]{0,1}\d{4}");
And this is the results:
var regex = new Regex(#"^\d{6,8}[-|(\s)]{0,1}\d{4}");
Match m = regex.Match("840204-2344");
Console.WriteLine(m.Success); // Outputs True
Match m = regex.Match("19840204-2344");
Console.WriteLine(m.Success); // Outputs True
Match m = regex.Match("19840204-23");
Console.WriteLine(m.Success); // Outputs false
Match m = regex.Match("19840204-2323423423");
Console.WriteLine(m.Success); // Outputs true, and this is what I don't want

The \d{6,8} pattern matches 6, 7 or 8 digits, so that will already invalidate your regex pattern. Besdies, [-|(\s)]{0,1} matches 1 or 0 -, (, ), | or whitespace chars, and will also match strings like 19840204|2323, 19840204(2323 and 19840204)2323.
You may use
^\d{6}(?:\d{2})?[-\s]?\d{4}$
See the regex demo.
Details
^ - start of string
\d{6} - 6 digits
(?:\d{2})? - optional 2 digits
[-\s]? - 1 or 0 - or whitespaces
\d{4} - 4 digits
$ - end of string.
To make \d only match ASCII digits, pass RegexOptions.ECMAScriptoption. Example:
var res = Regex.IsMatch(s, #"^\d{6}(?:\d{2})?[-\s]?\d{4}$", RegexOptions.ECMAScript);

You are forgetting the $ at the end:
var regex = new Regex(#"^(\d{6}|\d{8})-\d{4}$");
If you want to match the social security number anywhere in a string, you van also use \b to test for boundaries:
var regex = new Regex(#"\b(\d{6}|\d{8})-\d{4}\b");
Edit: I corrected the RegEx to fix the problems mentioned in the comments. The commentors are right, of course. In my earlier post I just wanted to explain why the RegEx matched the longer string.

Regex to get everything starting with # and removing everything after any non-included characters

I have the following:
Regex RgxUrl = new Regex("[^a-zA-Z0-9-_]");
foreach (var item in source.Split(' ').Where(s => s.StartsWith("#")))
{
var mention = item.Replace("#", "");
mention = RgxUrl.Replace(mention, "");
usernames.Add(mention);
}
CURRENT INPUT > OUTPUT
#fish and fries are #good > fish, good
#fish and fries and #Mary's beer are #good > fish, good, marys
DESIRED INPUT > OUTPUT
#fish and fries are #good > fish, good
#fish and fries and #Mary's beer are #good > fish, good, Mary
The key here is to remove anything that's after an offending character. How can this be achieved?

You split a string with a space, check if a chunk starts with #, then if yes, remove all the # symbols in the string, then use a regex to remove all non-alphanumeric, - and _ chars in the string and then add it to the list.
You can do that with a single regex:
var res = Regex.Matches(source, #"(?<!\S)#([a-zA-Z0-9-_]+)")
.Cast<Match>()
.Select(m=>m.Groups[1].Value)
.ToList();
Console.WriteLine(string.Join("; ", res)); // demo
usernames.AddRange(res); // in your code
See the C# demo
Pattern details:
(?<!\S) - there must not be a non-whitespace symbol immediately to the left of the current location (i.e. there must be a whitespace or start of string) (this lookbehind is here because the original code split the string with whitespace)
# - a # symbol (it is not part of the subsequent group because this symbol was removed in the original code)
([a-zA-Z0-9-_]+) - Capturing Group 1 (accessed with m.Groups[1].Value) matching one or more ASCII letters, digits, - and _ symbols.

Regular expression match all numbers after the last dash?

Trying to find the last instance of numbers after last dash in a string so
test-123-2-456 would return 456
123-test would return ""
123-test-456 would return 456
123-test-456sdfsdf would return 456
123-test-asd456 would return 456
The expression, #"[^-]*$", does not match the numbers though, and I have tried using [\d] but to no avail.

Sure, the simplest solution would be something like this:
(\d+)[^-]*$
This will match one or more digits, captured in group 1, followed by zero or more of any character other than a hyphen, followed by the end of the string. In other words, it will match any sequence of digits as long as there are no hyphens between that sequence and the end of the string. You then just have to extract group 1 from the match. For example:
var inputs = new[] {
"test-123-2-456",
"123-test",
"123-test-456",
"123-test-456sdfsdf",
"123-test-asd456"
};
foreach(var str in inputs)
{
var m = Regex.Match(str, #"(\d+)[^-]*$");
Console.WriteLine("{0} --> {1}", str, m.Groups[1].Value);
}
Produces:
test-123-2-456 --> 456
123-test -->
123-test-456 --> 456
123-test-456sdfsdf --> 456
123-test-asd456 --> 456
Alternatively, if you could use a negative lookahead like this:
\d+(?!.*-)
This will match one or more digit characters so long as they are not followed by a hyphen. Only the digits will be included in the match.
Note that these two options behave differently if there are two or more sets of numbers after the last -, e.g. foo-123bar456. In this case it's not entirely clear what you want to happen, but the first pattern will simply match everything starting from the first sequence of digits to the end (123bar456) with group 1 only containing the first sequence of digits (123). If you'd like to change this so that it only captures the last sequence of digits, place a \d inside the character class (i.e. (\d+)[^\d-]*$). The second second pattern would produce a separate match for each sequence digits (in this example, 123 and 456) but the Regex.Match method will only give you the first match.

I suggest to apply two regex-functions. Take the result of the first one as the input for the second one.
The first regex is:
-[0-9]+[^-]+$ // Take the last peace of your string lead by a minus (-)
// followed by digits ([0-9]+)
// and some ugly rest that doesn't contain another minus ([^-]+$)
The second regex is:
-[0-9]+ // Seperate the relevant digits from the ugly rest
// You know that there can only be one minus + digits part in it
Tested here: http://derekslager.com/blog/posts/2007/09/a-better-dotnet-regular-expression-tester.ashx

The latest group from this RegEx can get the last number for you:
[^-A-z][0-9]+[^A-z]
If you are looking at groups, you can write this code by matching groups to get the latest number:
var inputs = new[] {
"test-123-2-456",
"123-test",
"123-test-456",
"123-test-456sdfsdf",
"123-test-asd456"
};
var m = Regex.Match(str, #"([0-9]*)");
if(m.Groups.Length>1) //This will avoid the values starting with numbers only.
Console.WriteLine("{0} --> {1}", str, m.Groups[m.Groups.Length-1].Value);