Ignoring accented letters in string comparison

Question

I need to compare 2 strings in C# and treat accented letters the same as non-accented letters. For example:

string s1 = "hello";
string s2 = "héllo";

s1.Equals(s2, StringComparison.InvariantCultureIgnoreCase);
s1.Equals(s2, StringComparison.OrdinalIgnoreCase);

These 2 strings need to be the same (as far as my application is concerned), but both of these statements evaluate to false. Is there a way in C# to do this?

Answer 1

try this overload on the String.Compare Method.

String.Compare Method (String, String, Boolean, CultureInfo)

It produces a int value based on the compare operations including cultureinfo. the example in the page compares "Change" in en-US and en-CZ. CH in en-CZ is a single "letter".

example from the link

using System;
using System.Globalization;

class Sample {
    public static void Main() {
    String str1 = "change";
    String str2 = "dollar";
    String relation = null;

    relation = symbol( String.Compare(str1, str2, false, new CultureInfo("en-US")) );
    Console.WriteLine("For en-US: {0} {1} {2}", str1, relation, str2);

    relation = symbol( String.Compare(str1, str2, false, new CultureInfo("cs-CZ")) );
    Console.WriteLine("For cs-CZ: {0} {1} {2}", str1, relation, str2);
    }

    private static String symbol(int r) {
    String s = "=";
    if      (r < 0) s = "<";
    else if (r > 0) s = ">";
    return s;
    }
}
/*
This example produces the following results.
For en-US: change < dollar
For cs-CZ: change > dollar
*/

therefor for accented languages you will need to get the culture then test the strings based on that.

http://msdn.microsoft.com/en-us/library/hyxc48dt.aspx

Answer 2

The following method CompareIgnoreAccents(...) works on your example data. Here is the article where I got my background information: http://www.codeproject.com/KB/cs/EncodingAccents.aspx

private static bool CompareIgnoreAccents(string s1, string s2)
{
    return string.Compare(
        RemoveAccents(s1), RemoveAccents(s2), StringComparison.InvariantCultureIgnoreCase) == 0;
}

private static string RemoveAccents(string s)
{
    Encoding destEncoding = Encoding.GetEncoding("iso-8859-8");

    return destEncoding.GetString(
        Encoding.Convert(Encoding.UTF8, destEncoding, Encoding.UTF8.GetBytes(s)));
}

I think an extension method would be better:

public static string RemoveAccents(this string s)
{
    Encoding destEncoding = Encoding.GetEncoding("iso-8859-8");

    return destEncoding.GetString(
        Encoding.Convert(Encoding.UTF8, destEncoding, Encoding.UTF8.GetBytes(s)));
}

Then the use would be this:

if(string.Compare(s1.RemoveAccents(), s2.RemoveAccents(), true) == 0) {
   ...

Answer 3

Write a method normalize(String s) that takes in a string and turns accented letters into non accented one. Then instead of comparing string x to string y, compare normalize(string x) to normalize(string y).

Answer 4

Here's a function that strips diacritics from a string:

static string RemoveDiacritics(string sIn)
{
  string sFormD = sIn.Normalize(NormalizationForm.FormD);
  StringBuilder sb = new StringBuilder();

  foreach (char ch in sFormD)
  {
    UnicodeCategory uc = CharUnicodeInfo.GetUnicodeCategory(ch);
    if (uc != UnicodeCategory.NonSpacingMark)
    {
      sb.Append(ch);
    }
  }

  return (sb.ToString().Normalize(NormalizationForm.FormC));
}

More details here.

The principle is that is it turns 'é' into 2 successive chars 'e', acute. It then iterates through the chars and skips the diacritics.

"héllo" becomes "he<acute>llo", which in turn becomes "hello".

Debug.Assert("hello"==RemoveDiacritics("héllo"));

This line doesn't assert, which is what you want.