<?php

/**
 * @package Classes
 * @author Sho Kuwamoto <[email protected]>
 * @link http://kuwamoto.org/2007/12/17/improved-pluralizing-in-php-actionscript-and-ror/ Source
 */

class Inflect
{
	/**
	 * The plural form of a word
	 * @var array
	 */
    static $plural = array(
        '/(quiz)$/i'               => '$1zes',
        '/^(ox)$/i'                => '$1en',
        '/([m|l])ouse$/i'          => '$1ice',
        '/(matr|vert|ind)ix|ex$/i' => '$1ices',
        '/(x|ch|ss|sh)$/i'         => '$1es',
        '/([^aeiouy]|qu)y$/i'      => '$1ies',
        '/(hive)$/i'               => '$1s',
        '/(?:([^f])fe|([lr])f)$/i' => '$1$2ves',
        '/(shea|lea|loa|thie)f$/i' => '$1ves',
        '/sis$/i'                  => 'ses',
        '/([ti])um$/i'             => '$1a',
        '/(tomat|potat|ech|her|vet)o$/i'=> '$1oes',
        '/(bu)s$/i'                => '$1ses',
        '/(alias)$/i'              => '$1es',
        '/(octop)us$/i'            => '$1i',
        '/(ax|test)is$/i'          => '$1es',
        '/(us)$/i'                 => '$1es',
        '/s$/i'                    => 's',
        '/$/'                      => 's'
    );

	/**
	 * The singular form of a word
	 * @var array
	 */
    static $singular = array(
        '/(quiz)zes$/i'             => '$1',
        '/(matr)ices$/i'            => '$1ix',
        '/(vert|ind)ices$/i'        => '$1ex',
        '/^(ox)en$/i'               => '$1',
        '/(alias)es$/i'             => '$1',
        '/(octop|vir)i$/i'          => '$1us',
        '/(cris|ax|test)es$/i'      => '$1is',
        '/(shoe)s$/i'               => '$1',
        '/(o)es$/i'                 => '$1',
        '/(bus)es$/i'               => '$1',
        '/([m|l])ice$/i'            => '$1ouse',
        '/(x|ch|ss|sh)es$/i'        => '$1',
        '/(m)ovies$/i'              => '$1ovie',
        '/(s)eries$/i'              => '$1eries',
        '/([^aeiouy]|qu)ies$/i'     => '$1y',
        '/([lr])ves$/i'             => '$1f',
        '/(tive)s$/i'               => '$1',
        '/(hive)s$/i'               => '$1',
        '/(li|wi|kni)ves$/i'        => '$1fe',
        '/(shea|loa|lea|thie)ves$/i'=> '$1f',
        '/(^analy)ses$/i'           => '$1sis',
        '/((a)naly|(b)a|(d)iagno|(p)arenthe|(p)rogno|(s)ynop|(t)he)ses$/i'  => '$1$2sis',
        '/([ti])a$/i'               => '$1um',
        '/(n)ews$/i'                => '$1ews',
        '/(h|bl)ouses$/i'           => '$1ouse',
        '/(corpse)s$/i'             => '$1',
        '/(us)es$/i'                => '$1',
        '/s$/i'                     => ''
    );

	/**
	 * Words that aren't easily desribable via generic regex
	 * @var array
	 */
    static $irregular = array(
        'move'   => 'moves',
        'foot'   => 'feet',
        'goose'  => 'geese',
        'sex'    => 'sexes',
        'child'  => 'children',
        'man'    => 'men',
        'tooth'  => 'teeth',
        'person' => 'people'
    );

	/**
	 * Words that can be used as singular or plural without change 
	 * @var array
	 */
    static $uncountable = array(
        'sheep',
        'fish',
        'deer',
        'series',
        'species',
        'money',
        'rice',
        'information',
        'equipment'
    );

	/**
	 * Unconditionally pluralize a word
	 * @param string $string The string to pluralize
	 * @return string The pluralized string
	 */
    public static function pluralize( $string )
    {
        // save some time in the case that singular and plural are the same
        if ( in_array( strtolower( $string ), self::$uncountable ) )
            return $string;

        // check for irregular singular forms
        foreach ( self::$irregular as $pattern => $result )
        {
            $pattern = '/' . $pattern . '$/i';

            if ( preg_match( $pattern, $string ) )
                return preg_replace( $pattern, $result, $string);
        }

        // check for matches using regular expressions
        foreach ( self::$plural as $pattern => $result )
        {
            if ( preg_match( $pattern, $string ) )
                return preg_replace( $pattern, $result, $string );
        }

        return $string;
    }

	/**
	 * Unconditionally singularize a word
	 * @param string $string The string to singularize
	 * @return string The singularized string
	 */
    public static function singularize( $string )
    {
        // save some time in the case that singular and plural are the same
        if ( in_array( strtolower( $string ), self::$uncountable ) )
            return $string;

        // check for irregular plural forms
        foreach ( self::$irregular as $result => $pattern )
        {
            $pattern = '/' . $pattern . '$/i';

            if ( preg_match( $pattern, $string ) )
                return preg_replace( $pattern, $result, $string);
        }

        // check for matches using regular expressions
        foreach ( self::$singular as $pattern => $result )
        {
            if ( preg_match( $pattern, $string ) )
                return preg_replace( $pattern, $result, $string );
        }

        return $string;
    }

	/**
	 * Conditionally pluralize a word
	 * @param int $count The number of items $string references
	 * @param string $string The word to pluralize
	 * @return string "{$count} " . $pluralized_string
	 */
    public static function pluralize_if($count, $string)
    {
        if ($count == 1)
            return "1 $string";
        else
            return $count . " " . self::pluralize($string);
    }
}

?>

http://kuwamoto.org/2007/12/17/improved-pluralizing-in-php-actionscript-and-ror/Source

Inflection Class

PHP