How to replace each digit in a string with a different character?

Question

I am trying to get a string, for example, "e1e2e3" to have each digit replaced with a different character, which in this case would be a random number. Whereas instead of e1e2e3, it could be something like e5e9e1 because each number is replaced with a random one.

I tried

string txt = textBox1.Text;
Regex digits = new Regex(@"\d", RegexOptions.None);
Random rand = new Random();
txt = digits.Replace(txt, rand.Next(0, 9).ToString());
MessageBox.Show(txt);

The problem is, every single number is replaced with the same random number. "e1e2e3" would then be something like "e2e2e2" where each number is the same.

Do you want all 1's to be replaced with the same random digit or do you want them to be different? — Hans Kilian
– Hans Kilian, Commented Jun 24, 2021 at 9:01
You would need to use the overload of Replace that takes a MatchEvaluator. — ProgrammingLlama
– ProgrammingLlama, Commented Jun 24, 2021 at 9:04

The fourth bird · Accepted Answer · 2021-06-24 09:55:33Z

3

You are almost there, you can use the callback of Regex.Replace to create a random value for each replacement, instead of using a single random value.

If you just want to match digits 0-9 you can use [0-9] instead of \d as the latter could match all Unicode digits

string txt = textBox1.Text;
Regex digits = new Regex(@"\d", RegexOptions.None);
Random rand = new Random();
txt = digits.Replace(txt, match => rand.Next(0, 9).ToString());
MessageBox.Show(txt);

See a C# demo

edited Jun 24, 2021 at 9:55

answered Jun 24, 2021 at 9:34

The fourth bird

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fubo · Accepted Answer · 2021-06-24 11:22:27Z

2

approach without RegEx

string txt = "e1e2e3";           
Random rand = new Random();
string res = string.Concat(txt.Select(x => char.IsDigit(x)?(char)('0'+rand.Next(0, 9)):x));

Side note to the second int parameter of Next(int,int)

The exclusive upper bound of the random number returned. maxValue must be greater than or equal to minValue.

if you want values between 0 and 9, you should use Next(0, 10)

edited Jun 24, 2021 at 11:22

answered Jun 24, 2021 at 9:10

fubo

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