Question

I have a situation..
Having a string which can contain numbers,letters, and some symbols, I want to make an extraction from it or to make some replacements based on some “rules”.
I thing the best is to give some examples of possible situations and what I want to do (display):

String           Display1   or  Display2

AB_X345           X345         or  ###X345  
AB_1234            1234        or  ###1234  
X987_TEXT_4567    X9874567     or  X987######4567  
X987TEXT4567      X9874567     or  X987####4567  
X798TEXT          X798         or  X798####  
789TEXT            789         or  789####  
X400              X400         or  X400   

So practically when I find an X followed by numbers I want to display them. If some text appear, I don’t want it displayed or I want it masked with a character(#).
In case no X is present, I want to display only the numbers.
Is Regex the easyest way of doing this? (I am not familiar with regex-just had a bird’s eye view on it).
Can all the rules be gathered in a single regex expression or is to complicated?

Thank you for any sugestions

Answer 1

That’s easy:

resultString = Regex.Replace(subjectString, 
    @"\D       # Match a non-digit character
    (?<!       # unless...
     X         #  it's an X
     (?=\d)    #  which is followed by a digit.
    )          # End of lookbehind", 
    "", RegexOptions.IgnorePatternWhitespace);

Change the last line to

    "#", RegexOptions.IgnorePatternWhitespace);

to mask the characters with # instead of removing them.