How to find and replace every nth character occurrence using C# or regex? Conversion from Javascript to C#

Question

I need to Find and replace every 3rd character occurrence in a given string and replace it with H.
Can be done in C# or Regex or any other.

I found this Javascript code that does the same thing and would like to convert it into a C# code. Can you please assist ?

Found here

str = str.replace(/((?:[^x]*x){2}[^x]*)x/g, '$1y');  
  
let str = 'I amx nexver axt hoxme on Sxundxaxs';  
let n = 3;  
let ch = 'x';  
  
let regex = new RegExp("((?:[^" +ch+ "]*" +ch+ "){" + (n-1) + "}[^" +ch+ "]*)" +ch, "g");  
  
str = str.replace(regex, '$1y');  
  
console.log(str);  
//=> I amx nexver ayt hoxme on Sxundyaxs  

Answer 1

@Anonymous , Welcome to Microsoft Q&A, you could try the following link to convert the Javascript to c#.

     var ch = 'x';  
    var n = 3;  
    var str = "I amx nexver axt hoxme on Sxundxaxs";  
    var re = new Regex("((?:[^" + ch + "]*" + ch + "){" + (n - 1) + "}[^" + ch + "]*)" + ch);  
    var result = re.Replace(str, "${1}y");  
    Console.WriteLine(result);  

Tested result:

Hope this could help you.

Best Regards,
Jack

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Answer 2

HI @Anonymous

You can try below code to get your desire result.

var stringToApply = "74Mercedes1980";  
var nth = 3;  
var charToReplace = 'H';  
var regex = new Regex("(\\S{" + (nth - 1) + "})\\S");  
var outstr = regex.Replace(stringToApply, "$1" + charToReplace);  
Console.WriteLine(outstr);  
  
//output: 74HerHedHs1H80  

https://stackoverflow.com/questions/72850434/c-sharp-how-to-find-and-replace-every-nth-character-occurrence-using-c-sharp-o