Develop Reference

Simplify regex code in C#: Add a space between a digit/decimal and unit

I have a regex code written in C# that basically adds a space between a number and a unit with some exceptions:
dosage_value = Regex.Replace(dosage_value, #"(\d)\s+", #"$1");
dosage_value = Regex.Replace(dosage_value, #"(\d)%\s+", #"$1%");
dosage_value = Regex.Replace(dosage_value, #"(\d+(\.\d+)?)", #"$1 ");
dosage_value = Regex.Replace(dosage_value, #"(\d)\s+%", #"$1% ");
dosage_value = Regex.Replace(dosage_value, #"(\d)\s+:", #"$1:");
dosage_value = Regex.Replace(dosage_value, #"(\d)\s+e", #"$1e");
dosage_value = Regex.Replace(dosage_value, #"(\d)\s+E", #"$1E");
Example:
10ANYUNIT
10:something
10 : something
10 %
40 e-5
40 E-05
should become
10 ANYUNIT
10:something
10: something
10%
40e-5
40E-05
Exceptions are: %, E, e and :.
I have tried, but since my regex knowledge is not top-notch, would someone be able to help me reduce this code with same expected results?
Thank you!

For your example data, you might use 2 capture groups where the second group is in an optional part.
In the callback of replace, check if capture group 2 exists. If it does, use is in the replacement, else add a space.
(\d+(?:\.\d+)?)(?:\s*([%:eE]))?
( Capture group 1
\d+(?:\.\d+)? match 1+ digits with an optional decimal part
) Close group 1
(?: Non capture group to match a as a whole
\s*([%:eE]) Match optional whitespace chars, and capture 1 of % : e E in group 2
)? Close non capture group and make it optional
.NET regex demo
string[] strings = new string[]
{
"10ANYUNIT",
"10:something",
"10 : something",
"10 %",
"40 e-5",
"40 E-05",
};
string pattern = #"(\d+(?:\.\d+)?)(?:\s*([%:eE]))?";
var result = strings.Select(s =>
Regex.Replace(
s, pattern, m =>
m.Groups[1].Value + (m.Groups[2].Success ? m.Groups[2].Value : " ")
)
);
Array.ForEach(result.ToArray(), Console.WriteLine);
Output
10 ANYUNIT
10:something
10: something
10%
40e-5
40E-05
As in .NET \d can also match digits from other languages, \s can also match a newline and the start of the pattern might be a partial match, a bit more precise match can be:
\b([0-9]+(?:\.[0-9]+)?)(?:[\p{Zs}\t]*([%:eE]))?

I think you need something like this:
dosage_value = Regex.Replace(dosage_value, #"(\d+(\.\d*)?)\s*((E|e|%|:)+)\s*", #"$1$3 ");
Group 1 - (\d+(\.\d*)?)
Any number like 123 1241.23
Group 2 - ((E|e|%|:)+)
Any of special symbols like E e % :
Group 1 and Group 2 could be separated with any number of whitespaces.
If it's not working as you asking, please provide some samples to test.

For me it's too complex to be handled just by one regex. I suggest splitting into separate checks. See below code example - I used four different regexes, first is described in detail, the rest can be deduced based on first explanation.
using System.Text.RegularExpressions;
var testStrings = new string[]
{
"10mg",
"10:something",
"10 : something",
"10 %",
"40 e-5",
"40 E-05",
};
foreach (var testString in testStrings)
{
Console.WriteLine($"Input: '{testString}', parsed: '{RegexReplace(testString)}'");
}
string RegexReplace(string input)
{
// First look for exponential notation.
// Pattern is: match zero or more whitespaces \s*
// Then match one or more digits and store it in first capturing group (\d+)
// Then match one ore more whitespaces again.
// Then match part with exponent ([eE][-+]?\d+) and store it in second capturing group.
// It will match lower or uppercase 'e' with optional (due to ? operator) dash/plus sign and one ore more digits.
// Then match zero or more white spaces.
var expForMatch = Regex.Match(input, #"\s*(\d+)\s+([eE][-+]?\d+)\s*");
if(expForMatch.Success)
{
return $"{expForMatch.Groups[1].Value}{expForMatch.Groups[2].Value}";
}
var matchWithColon = Regex.Match(input, #"\s*(\d+)\s*:\s*(\w+)");
if (matchWithColon.Success)
{
return $"{matchWithColon.Groups[1].Value}:{matchWithColon.Groups[2].Value}";
}
var matchWithPercent = Regex.Match(input, #"\s*(\d+)\s*%");
if (matchWithPercent.Success)
{
return $"{matchWithPercent.Groups[1].Value}%";
}
var matchWithUnit = Regex.Match(input, #"\s*(\d+)\s*(\w+)");
if (matchWithUnit.Success)
{
return $"{matchWithUnit.Groups[1].Value} {matchWithUnit.Groups[2].Value}";
}
return input;
}
Output is:
Input: '10mg', parsed: '10 mg'
Input: '10:something', parsed: '10:something'
Input: '10 : something', parsed: '10:something'
Input: '10 %', parsed: '10%'
Input: '40 e-5', parsed: '40e-5'
Input: '40 E-05', parsed: '40E-05'

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)

c# regex to parse columns in a txt file

I have a text file looks like this
FieldA FieldB FieldC FieldD FieldE
001 中文 15% 语言
002 法文 20 12% 外文
003 英文 21 外文
004 西班牙语 10% 外文
so basically I have the file read in and split into lines. Now I would like to use regex to split each line into fields. As you can see some fields in the column are actually empty, the fields may not in fixed width, but is separated by at least one white space. Some fields contains Chinese characters.
May I know how to do this? Thanks.

string s = "001 中文 15% 语言";
Match m = Regex.Match(s,
#"(?<A>\d*)\s*" + // Field A: any number of digits
#"(?<B>\p{L}*)\s*" + // Field B: any number of letters
#"(?<C>\d*)\s+" + // Field C: any number of digits
#"(?<D>(\d+%)?)\s*" + // Field D: one or more digits followed by '%', or nothing
#"(?<E>\p{L}*)"); // Field E: any number of letters
string fieldA = m.Groups["A"].Value; // "001"
string fieldB = m.Groups["B"].Value; // "中文"
string fieldC = m.Groups["C"].Value; // ""
string fieldD = m.Groups["D"].Value; // "15%"
string fieldE = m.Groups["E"].Value; // "语言"
All fields are optional. If a field is not present, it will be captured as an empty string, like in fieldC above.

/\s*(\d*)\s*([^\d\s]*)\s*(\d*)\s\s*(\d*%?)\s*([^\d\s]*)/
Here is a regex that will capture all of the content you want, use it on each line.
\s* //any number of whitespace
(\d*) //any number of digits
\s* //any number of whitespace
([^\d\s]*) //any number of characters that aren't whitespace or digits
\s* //any number of whitespace
(\d*)\s //any number of digits with a space after it
\s* //any number of whitespace
(\d*%?) //any number of digits with an optional %
\s* //any number of whitespace
([^\d\s]*) //any number of characters that aren't whitespace or digits

Regex masking of words that contain a digit

Trying to come up with a 'simple' regex to mask bits of text that look like they might contain account numbers.
In plain English:
any word containing a digit (or a train of such words) should be matched
leave the last 4 digits intact
replace all previous part of the matched string with four X's (xxxx)
So far
I'm using the following:
[\-0-9 ]+(?<m1>[\-0-9]{4})
replacing with
xxxx${m1}
But this misses on the last few samples below
sample data:
123456789
a123b456
a1234b5678
a1234 b5678
111 22 3333
this is a a1234 b5678 test string
Actual results
xxxx6789
a123b456
a1234b5678
a1234 b5678
xxxx3333
this is a a1234 b5678 test string
Expected results
xxxx6789
xxxxb456
xxxx5678
xxxx5678
xxxx3333
this is a xxxx5678 test string
Is such an arrangement possible with a regex replace?
I think I"m going to need some greediness and lookahead functionality, but I have zero experience in those areas.

This works for your example:
var result = Regex.Replace(
input,
#"(?<!\b\w*\d\w*)(?<m1>\s?\b\w*\d\w*)+",
m => "xxxx" + m.Value.Substring(Math.Max(0, m.Value.Length - 4)));
If you have a value like 111 2233 33, it will print xxxx3 33. If you want this to be free from spaces, you could turn the lambda into a multi-line statement that removes whitespace from the value.
To explain the regex pattern a bit, it's got a negative lookbehind, so it makes sure that the word behind it does not have a digit in it (with optional word characters around the digit). Then it's got the m1 portion, which looks for words with digits in them. The last four characters of this are grabbed via some C# code after the regex pattern resolves the rest.

I don't think that regex is the best way to solve this problem and that's why I am posting this answer. For so complex situations, building the corresponding regex is too difficult and, what is worse, its clarity and adaptability is much lower than a longer-code approach.
The code below these lines delivers the exact functionality you are after, it is clear enough and can be easily extended.
string input = "this is a a1234 b5678 test string";
string output = "";
string[] temp = input.Trim().Split(' ');
bool previousNum = false;
string tempOutput = "";
foreach (string word in temp)
{
if (word.ToCharArray().Where(x => char.IsDigit(x)).Count() > 0)
{
previousNum = true;
tempOutput = tempOutput + word;
}
else
{
if (previousNum)
{
if (tempOutput.Length >= 4) tempOutput = "xxxx" + tempOutput.Substring(tempOutput.Length - 4, 4);
output = output + " " + tempOutput;
previousNum = false;
}
output = output + " " + word;
}
}
if (previousNum)
{
if (tempOutput.Length >= 4) tempOutput = "xxxx" + tempOutput.Substring(tempOutput.Length - 4, 4);
output = output + " " + tempOutput;
previousNum = false;
}

Have you tried this:
.*(?<m1>[\d]{4})(?<m2>.*)
with replacement
xxxx${m1}${m2}
This produces
xxxx6789
xxxx5678
xxxx5678
xxxx3333
xxxx5678 test string
You are not going to get 'a123b456' to match ... until 'b' becomes a number. ;-)

Here is my really quick attempt:
(\s|^)([a-z]*\d+[a-z,0-9]+\s)+
This will select all of those test cases. Now as for C# code, you'll need to check each match to see if there is a space at the beginning or end of the match sequence (e.g., the last example will have the space before and after selected)
here is the C# code to do the replace:
var redacted = Regex.Replace(record, #"(\s|^)([a-z]*\d+[a-z,0-9]+\s)+",
match => "xxxx" /*new String("x",match.Value.Length - 4)*/ +
match.Value.Substring(Math.Max(0, match.Value.Length - 4)));

What RegEx string will find the last (rightmost) group of digits in a string?

Looking for a regex string that will let me find the rightmost (if any) group of digits embedded in a string. We only care about contiguous digits. We don't care about sign, commas, decimals, etc. Those, if found should simply be treated as non-digits just like a letter.
This is for replacement/incrementing purposes so we also need to grab everything before and after the detected number so we can reconstruct the string after incrementing the value so we need a tokenized regex.
Here's examples of what we are looking for:
"abc123def456ghi" should identify the'456'
"abc123def456ghi789jkl" should identify the'789'
"abc123def" should identify the'123'
"123ghi" should identify the'123'
"abc123,456ghi" should identify the'456'
"abc-654def" should identify the'654'
"abcdef" shouldn't return any match
As an example of what we want, it would be something like starting with the name 'Item 4-1a', extracting out the '1' with everything before being the prefix and everything after being the suffix. Then using that, we can generate the values 'Item 4-2a', 'Item 4-3a' and 'Item 4-4a' in a code loop.
Now If I were looking for the first set, this would be easy. I'd just find the first contiguous block of 0 or more non-digits for the prefix, then the block of 1 or more contiguous digits for the number, then everything else to the end would be the suffix.
The issue I'm having is how to define the prefix as including all (if any) numbers except the last set. Everything I try for the prefix keeps swallowing that last set, even when I've tried anchoring it to the end by basically reversing the above.

How about:
^(.*?)(\d+)(\D*)$
then increment the second group and concat all 3.
Explanation:
^ : Begining of string
( : start of 1st capture group
.*? : any number of any char not greedy
) : end group
( : start of 2nd capture group
\d+ : one or more digits
) : end group
( : start of 3rd capture group
\D* : any number of non digit char
) : end group
$ : end of string
The first capture group will match all characters until the first digit of last group of digits before the end of the string.
or if you can use named group
^(?<prefix>.*?)(?<number>\d+)(?<suffix>\D*)$

Try next regex:
(\d+)(?!.*\d)
Explanation:
(\d+) # One or more digits.
(?!.*\d) # (zero-width) Negative look-ahead: Don't find any characters followed with a digit.
EDIT (OFFTOPIC of the question):: This answer is incorrect but this question has already been answered in other posts so to avoid delete this one I will use this same regex other way, for example in Perl could be used like this to get same result as in C# (increment last digit):
s/(\d+)(?!.*\d)/$1 + 1/e;

You can also try little bit simpler version:
(\d+)[^\d]*$

This should do it:
Regex regexObj = new Regex(#"
# Grab last set of digits, prefix and suffix.
^ # Anchor to start of string.
(.*) # $1: Stuff before last set of digits.
(?<!\d) # Anchor start of last set of digits.
(\d+) # $2: Last set of one or more digits.
(\D*) # $3: Zero or more trailing non digits.
$ # Anchor to end of string.
", RegexOptions.IgnorePatternWhitespace);

What about not using Regex. Here's code snippet (for console)
string[] myStringArray = new string[] { "abc123def456ghi", "abc123def456ghi789jkl", "abc123def", "123ghi", "abcdef","abc-654def" };
char[] numberSet = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
char[] filterSet = new char[] {'a','b','c','d','e','f','g','h','i','j','k','l','m',
'n','o','p','q','r','s','t','u','v','w','x','y','z','-'};
foreach (string myString in myStringArray)
{
Console.WriteLine("your string - {0}",myString);
int index1 = myString.LastIndexOfAny(numberSet);
if (index1 == -1)
Console.WriteLine("no number");
else
{
string mySubString = myString.Substring(0,index1 + 1);
string prefix = myString.Substring(index1 + 1);
Console.WriteLine("prefix - {0}", prefix);
int index2 = mySubString.LastIndexOfAny(filterSet);
string suffix = myString.Substring(0, index2 + 1);
Console.WriteLine("suffix - {0}",suffix);
mySubString = mySubString.Substring(index2 + 1);
Console.WriteLine("number - {0}",mySubString);
Console.WriteLine("_________________");
}
}
Console.Read();