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# PorterStemmer.php

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    00001 <?php
    00025     class PorterStemmer
    00026     {
    00031         private static $regex_consonant = '(?:[bcdfghjklmnpqrstvwxz]|(?<=[aeiou])y|^y)';
    00032
    00033
    00038         private static $regex_vowel = '(?:[aeiou]|(?<![aeiou])y)';
    00039
    00040
    00046         private static $cache = array();
    00047
    00048
    00056         public static function Stem($word, $cache = false)
    00057         {
    00058             if (strlen($word) <= 2) {
    00059                 return $word;
    00060             }
    00061
    00062             // Check cache
    00063             if ($cache AND !empty(self::$cache[$word])) {
    00064                 return self::$cache[$word];
    00065             }
    00066
    00070             $word = preg_replace("/('ve|n't|'d)$/", '', $word);
    00071
    00072             $stem = self::step1ab($word);
    00073             $stem = self::step1c($stem);
    00074             $stem = self::step2($stem);
    00075             $stem = self::step3($stem);
    00076             $stem = self::step4($stem);
    00077             $stem = self::step5($stem);
    00078
    00079             // Store in cache
    00080             if ($cache) {
    00081                 self::$cache[$word] = $stem;
    00082             }
    00083
    00084             return $stem;
    00085         }
    00086
    00087
    00091         private static function step1ab($word)
    00092         {
    00093             // Part a
    00094             if (substr($word, -1) == 's') {
    00095
    00096                    self::replace($word, 'sses', 'ss')
    00097                 OR self::replace($word, 'ies', 'i')
    00098                 OR self::replace($word, 'ss', 'ss')
    00099                 OR self::replace($word, 's', '');
    00100             }
    00101
    00102             // Part b
    00103             if (substr($word, -2, 1) != 'e' OR !self::replace($word, 'eed', 'ee', 0)) { // First rule
    00104                 $v = self::$regex_vowel;
    00105
    00106                 // ing and ed
    00107                 if (   preg_match("#$v+#", substr($word, 0, -3)) && self::replace($word, 'ing', '')
    00108                     OR preg_match("#$v+#", substr($word, 0, -2)) && self::replace($word, 'ed', '')) { // Note use of && and OR, for precedence reasons
    00109
    00110                     // If one of above two test successful
    00111                     if (    !self::replace($word, 'at', 'ate')
    00112                         AND !self::replace($word, 'bl', 'ble')
    00113                         AND !self::replace($word, 'iz', 'ize')) {
    00114
    00115                         // Double consonant ending
    00116                         if (    self::doubleConsonant($word)
    00117                             AND substr($word, -2) != 'll'
    00118                             AND substr($word, -2) != 'ss'
    00119                             AND substr($word, -2) != 'zz') {
    00120
    00121                             $word = substr($word, 0, -1);
    00122
    00123                         } else if (self::m($word) == 1 AND self::cvc($word)) {
    00124                             $word .= 'e';
    00125                         }
    00126                     }
    00127                 }
    00128             }
    00129
    00130             return $word;
    00131         }
    00132
    00133
    00139         private static function step1c($word)
    00140         {
    00141             $v = self::$regex_vowel;
    00142
    00143             if (substr($word, -1) == 'y' && preg_match("#$v+#", substr($word, 0, -1))) {
    00144                 self::replace($word, 'y', 'i');
    00145             }
    00146
    00147             return $word;
    00148         }
    00149
    00150
    00156         private static function step2($word)
    00157         {
    00158             switch (substr($word, -2, 1)) {
    00159                 case 'a':
    00160                        self::replace($word, 'ational', 'ate', 0)
    00161                     OR self::replace($word, 'tional', 'tion', 0);
    00162                     break;
    00163
    00164                 case 'c':
    00165                        self::replace($word, 'enci', 'ence', 0)
    00166                     OR self::replace($word, 'anci', 'ance', 0);
    00167                     break;
    00168
    00169                 case 'e':
    00170                     self::replace($word, 'izer', 'ize', 0);
    00171                     break;
    00172
    00173                 case 'g':
    00174                     self::replace($word, 'logi', 'log', 0);
    00175                     break;
    00176
    00177                 case 'l':
    00178                        self::replace($word, 'entli', 'ent', 0)
    00179                     OR self::replace($word, 'ousli', 'ous', 0)
    00180                     OR self::replace($word, 'alli', 'al', 0)
    00181                     OR self::replace($word, 'bli', 'ble', 0)
    00182                     OR self::replace($word, 'eli', 'e', 0);
    00183                     break;
    00184
    00185                 case 'o':
    00186                        self::replace($word, 'ization', 'ize', 0)
    00187                     OR self::replace($word, 'ation', 'ate', 0)
    00188                     OR self::replace($word, 'ator', 'ate', 0);
    00189                     break;
    00190
    00191                 case 's':
    00192                        self::replace($word, 'iveness', 'ive', 0)
    00193                     OR self::replace($word, 'fulness', 'ful', 0)
    00194                     OR self::replace($word, 'ousness', 'ous', 0)
    00195                     OR self::replace($word, 'alism', 'al', 0);
    00196                     break;
    00197
    00198                 case 't':
    00199                        self::replace($word, 'biliti', 'ble', 0)
    00200                     OR self::replace($word, 'aliti', 'al', 0)
    00201                     OR self::replace($word, 'iviti', 'ive', 0);
    00202                     break;
    00203             }
    00204
    00205             return $word;
    00206         }
    00207
    00208
    00214         private static function step3($word)
    00215         {
    00216             switch (substr($word, -2, 1)) {
    00217                 case 'a':
    00218                     self::replace($word, 'ical', 'ic', 0);
    00219                     break;
    00220
    00221                 case 's':
    00222                        self::replace($word, 'alise', 'al', 0)
    00223                     OR self::replace($word, 'ness', '', 0);
    00224                     break;
    00225
    00226                 case 't':
    00227                        self::replace($word, 'icate', 'ic', 0)
    00228                     OR self::replace($word, 'iciti', 'ic', 0);
    00229                     break;
    00230
    00231                 case 'u':
    00232                     self::replace($word, 'ful', '', 0);
    00233                     break;
    00234
    00235                 case 'v':
    00236                     self::replace($word, 'ative', '', 0);
    00237                     break;
    00238
    00239                 case 'z':
    00240                     self::replace($word, 'alize', 'al', 0);
    00241                     break;
    00242             }
    00243
    00244             return $word;
    00245         }
    00246
    00247
    00253         private static function step4($word)
    00254         {
    00255             switch (substr($word, -2, 1)) {
    00256                 case 'a':
    00257                     self::replace($word, 'al', '', 1);
    00258                     break;
    00259
    00260                 case 'c':
    00261                        self::replace($word, 'ance', '', 1)
    00262                     OR self::replace($word, 'ence', '', 1);
    00263                     break;
    00264
    00265                 case 'e':
    00266                     self::replace($word, 'er', '', 1);
    00267                     break;
    00268
    00269                 case 'i':
    00270                     self::replace($word, 'ic', '', 1);
    00271                     break;
    00272
    00273                 case 'l':
    00274                        self::replace($word, 'able', '', 1)
    00275                     OR self::replace($word, 'ible', '', 1);
    00276                     break;
    00277
    00278                 case 'n':
    00279                        self::replace($word, 'ant', '', 1)
    00280                     OR self::replace($word, 'ement', '', 1)
    00281                     OR self::replace($word, 'ment', '', 1)
    00282                     OR self::replace($word, 'ent', '', 1);
    00283                     break;
    00284
    00285                 case 'o':
    00286                     if (substr($word, -4) == 'tion' OR substr($word, -4) == 'sion') {
    00287                        self::replace($word, 'ion', '', 1);
    00288                     } else {
    00289                         self::replace($word, 'ou', '', 1);
    00290                     }
    00291                     break;
    00292
    00293                 case 's':
    00294                     self::replace($word, 'ism', '', 1);
    00295                     break;
    00296
    00297                 case 't':
    00298                        self::replace($word, 'ate', '', 1)
    00299                     OR self::replace($word, 'iti', '', 1);
    00300                     break;
    00301
    00302                 case 'u':
    00303                     self::replace($word, 'ous', '', 1);
    00304                     break;
    00305
    00306                 case 'v':
    00307                     self::replace($word, 'ive', '', 1);
    00308                     break;
    00309
    00310                 case 'z':
    00311                     self::replace($word, 'ize', '', 1);
    00312                     break;
    00313             }
    00314
    00315             return $word;
    00316         }
    00317
    00318
    00324         private static function step5($word)
    00325         {
    00326             // Part a
    00327             if (substr($word, -1) == 'e') {
    00328                 if (self::m(substr($word, 0, -1)) > 1) {
    00329                     self::replace($word, 'e', '');
    00330
    00331                 } else if (self::m(substr($word, 0, -1)) == 1) {
    00332
    00333                     if (!self::cvc(substr($word, 0, -1))) {
    00334                         self::replace($word, 'e', '');
    00335                     }
    00336                 }
    00337             }
    00338
    00339             // Part b
    00340             if (self::m($word) > 1 AND self::doubleConsonant($word) AND substr($word, -1) == 'l') {
    00341                 $word = substr($word, 0, -1);
    00342             }
    00343
    00344             return $word;
    00345         }
    00346
    00347
    00360         private static function replace(&$str, $check, $repl, $m = null)
    00361         {
    00362             $len = 0 - strlen($check);
    00363
    00364             if (substr($str, $len) == $check) {
    00365                 $substr = substr($str, 0, $len);
    00366                 if (is_null($m) OR self::m($substr) > $m) {
    00367                     $str = $substr . $repl;
    00368                 }
    00369
    00370                 return true;
    00371             }
    00372
    00373             return false;
    00374         }
    00375
    00376
    00392         private static function m($str)
    00393         {
    00394             $c = self::$regex_consonant;
    00395             $v = self::$regex_vowel;
    00396
    00397             $str = preg_replace("#^$c+#", '', $str);
    00398             $str = preg_replace("#$v+$#", '', $str);
    00399
    00400             preg_match_all("#($v+$c+)#", $str, $matches);
    00401
    00402             return count($matches[1]);
    00403         }
    00404
    00405
    00413         private static function doubleConsonant($str)
    00414         {
    00415             $c = self::$regex_consonant;
    00416
    00417             return preg_match("#$c{2}$#", $str, $matches) AND $matches[0]{0} == $matches[0]{1};
    00418         }
    00419
    00420
    00427         private static function cvc($str)
    00428         {
    00429             $c = self::$regex_consonant;
    00430             $v = self::$regex_vowel;
    00431
    00432             return     preg_match("#($c$v$c)$#", $str, $matches)
    00433                    AND strlen($matches[1]) == 3
    00434                    AND $matches[1]{2} != 'w'
    00435                    AND $matches[1]{2} != 'x'
    00436                    AND $matches[1]{2} != 'y';
    00437         }
    00438     }
    00439 ?>