linq string handling 2 chars in 1 lambda expression

Question

I've seen some interesting ways to handle strings with Linq:

For example, to hide numbers in a string by replacing them with X's I can do:

string strNum = "Hello, my number is ... 3456c456";

string strHidden = new String(strNum.ToCharArray()
     .Select(c => (!char.IsNumber(c)) ? c : 'X').ToArray());

Console.WriteLine(strHidden);

Is there a Linq way to do this where numbers are replaced only if the current character is a number AND the following two characters are numbers?

There's a lot of ways to tailor the approach above, but I am wondering if there is an easy-ish linq way to do it with multiple characters at a time.

EDIT: added requirement for current character to be a number as well.

Answer 1

Based on the interpretation in my comment, you can do this with LINQ:

string strHidden = new String(Enumerable.Range(0, strNum.Length)
    .Select(i => 
        char.IsNumber(strNum[i]) && 
        Enumerable.Range(i+1,2).All(j => j < strNum.Length && char.IsNumber(strNum[j]))
            ? 'X'
            : strNum[i])
    .ToArray());

Regular expression alternative:

var strHidden = Regex.Replace(strNum, @"\d(?=\d{2})", "X");

Much nicer, no?