How can i remove none alphabet chars from a string[]? [duplicate]

Answer 1

To help Konrad and keyboardP resolve their differences, I ran a benchmark test, using their code. It turns out that keyboardP's code is 10x faster than Konrad's code

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Text.RegularExpressions;

    namespace ConsoleApplication1
    {
        class Program
        {
            static void Main(string[] args)
            {
                string input = "asdf234!@#*advfk234098awfdasdfq9823fna943";
                DateTime start = DateTime.Now;
                for (int i = 0; i < 100000; i++)
                {
                    RemoveNonUnicodeLetters(input);
                }
                Console.WriteLine(DateTime.Now.Subtract(start).TotalSeconds);
                start = DateTime.Now;
                for (int i = 0; i < 100000; i++)
                {
                    RemoveNonUnicodeLetters2(input);
                }
                Console.WriteLine(DateTime.Now.Subtract(start).TotalSeconds);
            }
            public static string RemoveNonUnicodeLetters(string input)
            {
                StringBuilder sb = new StringBuilder();
                foreach (char c in input)
                {
                    if (Char.IsLetter(c))
                        sb.Append(c);
                }

                return sb.ToString();
            }
            public static string RemoveNonUnicodeLetters2(string input)
            {
                var result = Regex.Replace(input, "\\P{L}", "");
                return result;
            }
        }
    }

I got

0.12
1.2

as output

UPDATE:

To see if it is the Regex compilation that is slowing down the Regex method, I put the regex in a static variable that is only constructed once.

            static Regex rex = new Regex("\\P{L}");
            public static string RemoveNonUnicodeLetters2(string input)
            {
                var result = rex.Replace(input,m => "");
                return result;
            }

But this had no effect on the runtime.

Answer 2

keyboardP’s solution is decent – do consider it. But as I’ve argued in the comments, regular expressions are actually the correct tool for the job, you’re just making it unnecessarily complicated. The actual solution is a one-liner:

var result = Regex.Replace(input, "\\P{L}", "");

\P{…} specifies a Unicode character class we do not want to match (the opposite of \p{…}). L is the Unicode character class for letters.

Of course it makes sense to encapsulate this into a method, as keyboardP did. To avoid recompiling the regular expression over again, you should also consider pulling the regex creation out of the actual code (although this probably won’t give a big impact on performance):

static readonly Regex nonUnicodeRx = new Regex("\\P{L}");

public static string RemoveNonUnicodeLetters(string input) {
    return nonUnicodeRx.Replace(input, "");
}

Answer 3

You don't need a regex to clear non-letters. This will remove all non-unicode letters.

public string RemoveNonUnicodeLetters(string input)
{
    StringBuilder sb = new StringBuilder();
    foreach(char c in input)
    {
        if(Char.IsLetter(c))
           sb.Append(c);
    }

    return sb.ToString();
}

Alternatively, if you only want to allow Latin letters, you can use this

public string RemoveNonLatinLetters(string input)
{
    StringBuilder sb = new StringBuilder();
    foreach(char c in input)
    {
        if(c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
           sb.Append(c);
    }

    return sb.ToString();
}

Benchmark vs Regex

public static string RemoveNonUnicodeLetters(string input)
{
       StringBuilder sb = new StringBuilder();
       foreach (char c in input)
       {
            if (Char.IsLetter(c))
                sb.Append(c);
       }

            return sb.ToString();
}



static readonly Regex nonUnicodeRx = new Regex("\\P{L}");

public static string RemoveNonUnicodeLetters2(string input)
{
     return nonUnicodeRx.Replace(input, "");
}


static void Main(string[] args)
{

    Stopwatch sw = new Stopwatch();

    StringBuilder sb = new StringBuilder();


    //generate guids as input
    for (int j = 0; j < 1000; j++)
    {
        sb.Append(Guid.NewGuid().ToString());
    }

    string input = sb.ToString();

    sw.Start();

    for (int i = 0; i < 1000; i++)
    {
        RemoveNonUnicodeLetters(input);
    }

    sw.Stop();
    Console.WriteLine("SM: " + sw.ElapsedMilliseconds);

    sw.Restart();
    for (int i = 0; i < 1000; i++)
    {
        RemoveNonUnicodeLetters2(input);
    }

    sw.Stop();
    Console.WriteLine("RX: " + sw.ElapsedMilliseconds);


}

Output (SM = String Manipulation, RX = Regex)

SM: 581
RX: 9882

SM: 545
RX: 9557

SM: 664
RX: 10196