Converting Symbols, Accent Letters to English Alphabet

Reposting my post from How do I remove diacritics (accents) from a string in .NET?

This method works fine in java (purely for the purpose of removing diacritical marks aka accents).

It basically converts all accented characters into their deAccented counterparts followed by their combining diacritics. Now you can use a regex to strip off the diacritics.

import java.text.Normalizer;
import java.util.regex.Pattern;

public String deAccent(String str) {
    String nfdNormalizedString = Normalizer.normalize(str, Normalizer.Form.NFD); 
    Pattern pattern = Pattern.compile("\\p{InCombiningDiacriticalMarks}+");
    return pattern.matcher(nfdNormalizedString).replaceAll("");
}

Attempting to "convert them all" is the wrong approach to the problem.

Firstly, you need to understand the limitations of what you are trying to do. As others have pointed out, diacritics are there for a reason: they are essentially unique letters in the alphabet of that language with their own meaning / sound etc.: removing those marks is just the same as replacing random letters in an English word. This is before you even go onto consider the Cyrillic languages and other script based texts such as Arabic, which simply cannot be "converted" to English.

If you must, for whatever reason, convert characters, then the only sensible way to approach this it to firstly reduce the scope of the task at hand. Consider the source of the input - if you are coding an application for "the Western world" (to use as good a phrase as any), it would be unlikely that you would ever need to parse Arabic characters. Similarly, the Unicode character set contains hundreds of mathematical and pictorial symbols: there is no (easy) way for users to directly enter these, so you can assume they can be ignored.

By taking these logical steps you can reduce the number of possible characters to parse to the point where a dictionary based lookup / replace operation is feasible. It then becomes a small amount of slightly boring work creating the dictionaries, and a trivial task to perform the replacement. If your language supports native Unicode characters (as Java does) and optimises static structures correctly, such find and replaces tend to be blindingly quick.

This comes from experience of having worked on an application that was required to allow end users to search bibliographic data that included diacritic characters. The lookup arrays (as it was in our case) took perhaps 1 man day to produce, to cover all diacritic marks for all Western European languages.

If the need is to convert "òéışöç->oeisoc", you can use this a starting point :

public class AsciiUtils {
    private static final String PLAIN_ASCII =
      "AaEeIiOoUu"    // grave
    + "AaEeIiOoUuYy"  // acute
    + "AaEeIiOoUuYy"  // circumflex
    + "AaOoNn"        // tilde
    + "AaEeIiOoUuYy"  // umlaut
    + "Aa"            // ring
    + "Cc"            // cedilla
    + "OoUu"          // double acute
    ;

    private static final String UNICODE =
     "\u00C0\u00E0\u00C8\u00E8\u00CC\u00EC\u00D2\u00F2\u00D9\u00F9"             
    + "\u00C1\u00E1\u00C9\u00E9\u00CD\u00ED\u00D3\u00F3\u00DA\u00FA\u00DD\u00FD" 
    + "\u00C2\u00E2\u00CA\u00EA\u00CE\u00EE\u00D4\u00F4\u00DB\u00FB\u0176\u0177" 
    + "\u00C3\u00E3\u00D5\u00F5\u00D1\u00F1"
    + "\u00C4\u00E4\u00CB\u00EB\u00CF\u00EF\u00D6\u00F6\u00DC\u00FC\u0178\u00FF" 
    + "\u00C5\u00E5"                                                             
    + "\u00C7\u00E7" 
    + "\u0150\u0151\u0170\u0171" 
    ;

    // private constructor, can't be instanciated!
    private AsciiUtils() { }

    // remove accentued from a string and replace with ascii equivalent
    public static String convertNonAscii(String s) {
       if (s == null) return null;
       StringBuilder sb = new StringBuilder();
       int n = s.length();
       for (int i = 0; i < n; i++) {
          char c = s.charAt(i);
          int pos = UNICODE.indexOf(c);
          if (pos > -1){
              sb.append(PLAIN_ASCII.charAt(pos));
          }
          else {
              sb.append(c);
          }
       }
       return sb.toString();
    }

    public static void main(String args[]) {
       String s = 
         "The result : È,É,Ê,Ë,Û,Ù,Ï,Î,À,Â,Ô,è,é,ê,ë,û,ù,ï,î,à,â,ô,ç";
       System.out.println(AsciiUtils.convertNonAscii(s));
       // output : 
       // The result : E,E,E,E,U,U,I,I,A,A,O,e,e,e,e,u,u,i,i,a,a,o,c
    }
}

The JDK 1.6 provides the java.text.Normalizer class that can be used for this task.

See an example here

The problem with "converting" arbitrary Unicode to ASCII is that the meaning of a character is culture-dependent. For example, “ß” to a German-speaking person should be converted to "ss" while an English-speaker would probably convert it to “B”.

Add to that the fact that Unicode has multiple code points for the same glyphs.

The upshot is that the only way to do this is create a massive table with each Unicode character and the ASCII character you want to convert it to. You can take a shortcut by normalizing characters with accents to normalization form KD, but not all characters normalize to ASCII. In addition, Unicode does not define which parts of a glyph are "accents".

Here is a tiny excerpt from an app that does this:

switch (c)
{
    case 'A':
    case '\u00C0':  //  À LATIN CAPITAL LETTER A WITH GRAVE
    case '\u00C1':  //  Á LATIN CAPITAL LETTER A WITH ACUTE
    case '\u00C2':  //  Â LATIN CAPITAL LETTER A WITH CIRCUMFLEX
    // and so on for about 20 lines...
        return "A";
        break;

    case '\u00C6'://  Æ LATIN CAPITAL LIGATURE AE
        return "AE";
        break;

    // And so on for pages...
}

You could try using unidecode, which is available as a ruby gem and as a perl module on cpan. Essentially, it works as a huge lookup table, where each unicode code point relates to an ascii character or string.

There is no easy or general way to do what you want because it is just your subjective opinion that these letters look loke the latin letters you want to convert to. They are actually separate letters with their own distinct names and sounds which just happen to superficially look like a latin letter.

If you want that conversion, you have to create your own translation table based on what latin letters you think the non-latin letters should be converted to.

(If you only want to remove diacritial marks, there are some answers in this thread: How do I remove diacritics (accents) from a string in .NET? However you describe a more general problem)