CODEWITHSUNDEEP
c#string
user1037747
user1037747

Reputation: 1373

Replacing only single "\n" in string occurrence

I have a string in C# which can have multiple \n characters. For e.g. :

string tp = "Hello\nWorld \n\n\n !!";

If there is a single occurrence of \n I want to replace it with something, but if more than one \n appear together in the same place I want to leave them alone. So for the tp string above I want to replace the \n between Hello and World, because there is only one at that place, and leave the the three \n nearer the end of the string alone, because they appear in a group.

If I try to use the Replace() method in C# it replaces all of them. How can I resolve this issue?

Upvotes: 2

Views: 765

Answers (3)

ckerth
ckerth

Reputation: 316

Use regular expressions and combine negative lookbehind and lookahead:

 var test = "foo\nbar...foo\n\nbar\n\n\nfoo\r\nbar";
 var replaced = System.Text.RegularExpressions.Regex.Replace(test, "(?<!\n)\n(?!\n)", "_");
 // only first and last \n have been replaced

While searching through the input the regex "stops" at any "\n" it finds and verifies if no "\n" is one character behind the current position or ahead. Thus only single "\n" will be replaced.

Upvotes: 0

Caius Jard
Caius Jard

Reputation: 74605

A solution using loops:

char[] c = "\t"+ tp + "\t".ToCharArray();
for(int i = 1; i < c.Length - 1; i++)
  if(c[i] == '\n' && c[i-1] != '\n' && c[i+1] != '\n')
    c[i] = 'x';
tp = new string(c, 1, c.Length-2);

Upvotes: 0

Dmitrii Bychenko
Dmitrii Bychenko

Reputation: 186668

You can try using regular expressions: let's change \n into "*" whenever \n is single: 

using System.Text.RegularExpressions;

... 

string tp = "Hello\nWorld \n\n\n !!";

// "Hello*World \n\n\n !!";
string result = Regex.Replace(tp, "\n+", match => 
  match.Value.Length > 1 
    ? match.Value // multiple (>1) \n in row: leave intact
    : "*");       // single ocurrence: change into "*"

Upvotes: 3

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