Question

How do I strip non alphanumeric characters from a string and loose spaces in C# with Replace?

I want to keep a-z, A-Z, 0-9 and nothing more (not even ” ” spaces).

"Hello there(hello#)".Replace(regex-i-want, "");

should give

"Hellotherehello"

I have tried "Hello there(hello#)".Replace(@"[^A-Za-z0-9 ]", ""); but the spaces remain.

Answer 1

In your regex, you have excluded the spaces from being matched (and you haven’t used Regex.Replace() which I had overlooked completely…):

result = Regex.Replace("Hello there(hello#)", @"[^A-Za-z0-9]+", "");

should work. The + makes the regex a bit more efficient by matching more than one consecutive non-alphanumeric character at once instead of one by one.

If you want to keep non-ASCII letters/digits, too, use the following regex:

@"[^\p{L}\p{N}]+"

which leaves

BonjourmesélèvesGutenMorgenliebeSchüler

instead of

BonjourmeslvesGutenMorgenliebeSchler