Stripping out non-numeric characters in string

Solution 1:

There are many ways, but this should do (don't know how it performs with really large strings though):

private static string GetNumbers(string input)
{
    return new string(input.Where(c => char.IsDigit(c)).ToArray());
}

Solution 2:

Feels like a good fit for a regular expression.

var s = "40,595 p.a.";
var stripped = Regex.Replace(s, "[^0-9]", "");

"[^0-9]" can be replaced by @"\D" but I like the readability of [^0-9].

Solution 3:

An extension method will be a better approach:

public static string GetNumbers(this string text)
    {
        text = text ?? string.Empty;
        return new string(text.Where(p => char.IsDigit(p)).ToArray());
    }