Soundex

<?php
    /*
    Copyright (c) 2009, reusablecode.blogspot.com; some rights reserved.
    
    This work is licensed under the Creative Commons Attribution License. To view
    a copy of this license, visit http://creativecommons.org/licenses/by/3.0/ or
    send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California
    94305, USA.
    */
 
    // http://en.wikipedia.org/wiki/Soundex
 
    // Calculate soundex code for entire strings, and soundex digits for individual characters.
    function soundex($someString)
    {
        // Rather than write a separate function to convert consonants to digits, I decided to overload the soundex function.
        if (str_len($someString) == 1)
        {
            // Calculate soundex digit for an individual character.
            switch (strtolower($someString))
            {
                case "b":
                case "f":
                case "p":
                case "v":
                    return "1";
                    break;
                case "c":
                case "g":
                case "j":
                case "k":
                case "q":
                case "s":
                case "x":
                case "z":
                    return "2";
                    break;
                case "d":
                case "t":
                    return "3";
                    break;
                case "l":
                    return "4";
                    break;
                case "m":
                case "n":
                    return "5";
                    break;
                case "r":
                    return "6";
                default:
                    // Remove vowels right away instead of during a later step.
                    return "";
            }
        }
        else
        {
            // Calculate soundex code for an entire string.
 
            // The first letter remains intact.
            $result = strtoupper(substr($someString, 0, 1));
 
            // Replace consonants with digits and remove vowels.
            for ($i = 2; $i <= str_len($someString); $i++)
            {
                $result .= soundex(substr($someString, $i, 1));
            }
 
            // Collapse adjacent identical digits into a single digit of that value.
            for ($i = 1; $i <= 6; $i++)
            {
                while (substr_count($result, $i . $i) != 0)
                {
                    $result = str_replace($i . $i, $i, $result);
                }
            }
 
            // Return the starting letter and the first three remaining digits.
            // If needed, append zeroes to make it a letter and three digits.
            return str_pad(substr($result, 0, 4), 4, "0", STR_PAD_RIGHT);
        }
    }
?>