How do I remove all non alphanumeric characters fr

Question

How do I remove all non alphanumeric characters from a string except dash and space characters?

Answer 1

You can try:

   string s1= Regex.Replace(s,"[^A-Za-z0-9 _]","");

Where s is your string.

Answer 2

Using System.Linq

string withOutSpecialCharacters = new string(stringWithSpecialCharacters.Where(c =>char.IsLetterOrDigit(c) || char.IsWhiteSpace(c) || c == '-').ToArray());

Answer 3

I could have used RegEx, they can provide elegant solution but they can cause performane issues. Here is one solution

char[] arr = str.ToCharArray();

arr = Array.FindAll<char>(arr, (c => (char.IsLetterOrDigit(c) 
                                  || char.IsWhiteSpace(c) 
                                  || c == '-')));
str = new string(arr);

---

When using the compact framework (which doesn't have FindAll)

Replace FindAll with¹

char[] arr = str.Where(c => (char.IsLetterOrDigit(c) || 
                             char.IsWhiteSpace(c) || 
                             c == '-')).ToArray(); 

str = new string(arr);

---

¹ Comment by ShawnFeatherly

Answer 4

Want something quick?

public static class StringExtensions 
{
    public static string ToAlphaNumeric(this string self, params char[] allowedCharacters)
    {
        return new string(Array.FindAll(self.ToCharArray(), c => char.IsLetterOrDigit(c) || allowedCharacters.Contains(c)));
    }
}

This will allow you to specify which characters you want to allow as well.

Answer 5

Based on the answer for this question, I created a static class and added these. Thought it might be useful for some people.

public static class RegexConvert
{
    public static string ToAlphaNumericOnly(this string input)
    {
        Regex rgx = new Regex("[^a-zA-Z0-9]");
        return rgx.Replace(input, "");
    }

    public static string ToAlphaOnly(this string input)
    {
        Regex rgx = new Regex("[^a-zA-Z]");
        return rgx.Replace(input, "");
    }

    public static string ToNumericOnly(this string input)
    {
        Regex rgx = new Regex("[^0-9]");
        return rgx.Replace(input, "");
    }
}

Then the methods can be used as:

string example = "asdf1234!@#$";
string alphanumeric = example.ToAlphaNumericOnly();
string alpha = example.ToAlphaOnly();
string numeric = example.ToNumericOnly();

Answer 6

Here is a non-regex heap allocation friendly fast solution which was what I was looking for.

Unsafe edition.

public static unsafe void ToAlphaNumeric(ref string input)
{
    fixed (char* p = input)
    {
        int offset = 0;
        for (int i = 0; i < input.Length; i++)
        {
            if (char.IsLetterOrDigit(p[i]))
            {
                p[offset] = input[i];
                offset++;
            }
        }
        ((int*)p)[-1] = offset; // Changes the length of the string
        p[offset] = '\0';
    }
}

And for those who don't want to use unsafe or don't trust the string length hack.

public static string ToAlphaNumeric(string input)
{
    int j = 0;
    char[] newCharArr = new char[input.Length];

    for (int i = 0; i < input.Length; i++)
    {
        if (char.IsLetterOrDigit(input[i]))
        {
            newCharArr[j] = input[i];
            j++;
        }
    }

    Array.Resize(ref newCharArr, j);

    return new string(newCharArr);
}