Regex to exclude part of string on split

Question

I asked a similar question a few weeks ago on how to split a string based on a specific substring. However, I now want to do something a little different. I have a line that looks like this (sorry about the formatting):

What I want to do is split this line at all the newline \r\n sequences. However, I do not want to do this if there is a PA42 after one of the PA41 lines. I want the PA41 and the PA42 line that follows it to be on the same line. I have tried using several regex expressions to no avail. The output that I am looking for will ideally look like this:

This is the regex that I am currently using, but it does not quite accomplish what I am looking for.

string[] p = Regex.Split(parameterList[selectedIndex], @"[\r\n]+(?=PA41)");

If you need any clarifications, please feel free to ask.

Brad Christie · Accepted Answer · 2011-10-28 15:31:03Z

3

You're trying a positive look-ahead, you want a negative one. (Positive insures that the pattern does follow, whereas negative insures it does not.)

(\\r\\n)(?!PA42)

Works for me.

answered Oct 28, 2011 at 15:31

Brad Christie

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5 Comments

almostProgramming Over a year ago

Thank you. For some reason when I use this expression, it is not actually splitting unless I use @"(\r\n)(?!PA42)". However then it is also splitting the \r\n into a seperate line instead of preserving them at the end of the end of the PA## line.

Brad Christie Over a year ago

@almostProgramming: Are the "\r\n" characters literally a ` then an n` or r? or are they a carriage return and line feed? That will make all the difference in the pattern, but I don't know if you're showing them fort he sake of the question, or if they're characters.

almostProgramming Over a year ago

They are actually carriage returns and new lines. Sorry about that, I should have made that clear in the question.

Brad Christie Over a year ago

Then you can use a class [\r\n]+ or use (\r|\n)+ in the pattern as you want regex to mean those specific characters, not their escaped counter-parts.

almostProgramming Over a year ago

That did the trick. Thank you very much. I need to invest in a regex book, that's for sure.

FailedDev · Accepted Answer · 2011-10-28 15:30:54Z

3

string[] splitArray = Regex.Split(subjectString, @"\\r\\n(?!PA42)");

This should work. It uses a negative lookahead assertion to ensure that a \r\n sequence is not followed by PA42.

Explanation :

@"
\\         # Match the character “\” literally
r          # Match the character “r” literally
\\         # Match the character “\” literally
n          # Match the character “n” literally
(?!        # Assert that it is impossible to match the regex below starting at this position (negative lookahead)
   PA42       # Match the characters “PA42” literally
)
"

answered Oct 28, 2011 at 15:30

FailedDev

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1 Comment

FailedDev Over a year ago

@almostProgramming I was first! :) But it doesn't matter. Glad that your problem is solved one way or another.

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