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<?php
/**
* Copyright (c) 2005 Richard Heyes (http://www.phpguru.org/)
*
* All rights reserved.
*
* This script is free software.
*/
/**
* PHP5 Implementation of the Porter Stemmer algorithm. Certain elements
* were borrowed from the (broken) implementation by Jon Abernathy.
*
* Usage:
*
* $stem = ZemPorterStemmer::Stem($word);
*
* How easy is that?
*/
class ZemPorterStemmer
{
/**
* Regex for matching a consonant
* @var string
*/
private static $regex_consonant = '(?:[bcdfghjklmnpqrstvwxz]|(?<=[aeiou])y|^y)';
/**
* Regex for matching a vowel
* @var string
*/
private static $regex_vowel = '(?:[aeiou]|(?<![aeiou])y)';
/**
* Stems a word. Simple huh?
*
* @param string $word Word to stem
* @return string Stemmed word
*/
public static function Stem($word)
{
if (strlen($word) <= 2) {
return $word;
}
$word = self::step1ab($word);
$word = self::step1c($word);
$word = self::step2($word);
$word = self::step3($word);
$word = self::step4($word);
$word = self::step5($word);
return $word;
}
/**
* Step 1
*/
private static function step1ab($word)
{
// Part a
if (substr($word, -1) == 's') {
self::replace($word, 'sses', 'ss')
OR self::replace($word, 'ies', 'i')
OR self::replace($word, 'ss', 'ss')
OR self::replace($word, 's', '');
}
// Part b
if (substr($word, -2, 1) != 'e' OR !self::replace($word, 'eed', 'ee', 0)) { // First rule
$v = self::$regex_vowel;
// ing and ed
if ( preg_match("#$v+#", substr($word, 0, -3)) && self::replace($word, 'ing', '')
OR preg_match("#$v+#", substr($word, 0, -2)) && self::replace($word, 'ed', '')) { // Note use of && and OR, for precedence reasons
// If one of above two test successful
if ( !self::replace($word, 'at', 'ate')
AND !self::replace($word, 'bl', 'ble')
AND !self::replace($word, 'iz', 'ize')) {
// Double consonant ending
if ( self::doubleConsonant($word)
AND substr($word, -2) != 'll'
AND substr($word, -2) != 'ss'
AND substr($word, -2) != 'zz') {
$word = substr($word, 0, -1);
} else if (self::m($word) == 1 AND self::cvc($word)) {
$word .= 'e';
}
}
}
}
return $word;
}
/**
* Step 1c
*
* @param string $word Word to stem
*/
private static function step1c($word)
{
$v = self::$regex_vowel;
if (substr($word, -1) == 'y' && preg_match("#$v+#", substr($word, 0, -1))) {
self::replace($word, 'y', 'i');
}
return $word;
}
/**
* Step 2
*
* @param string $word Word to stem
*/
private static function step2($word)
{
switch (substr($word, -2, 1)) {
case 'a':
self::replace($word, 'ational', 'ate', 0)
OR self::replace($word, 'tional', 'tion', 0);
break;
case 'c':
self::replace($word, 'enci', 'ence', 0)
OR self::replace($word, 'anci', 'ance', 0);
break;
case 'e':
self::replace($word, 'izer', 'ize', 0);
break;
case 'g':
self::replace($word, 'logi', 'log', 0);
break;
case 'l':
self::replace($word, 'entli', 'ent', 0)
OR self::replace($word, 'ousli', 'ous', 0)
OR self::replace($word, 'alli', 'al', 0)
OR self::replace($word, 'bli', 'ble', 0)
OR self::replace($word, 'eli', 'e', 0);
break;
case 'o':
self::replace($word, 'ization', 'ize', 0)
OR self::replace($word, 'ation', 'ate', 0)
OR self::replace($word, 'ator', 'ate', 0);
break;
case 's':
self::replace($word, 'iveness', 'ive', 0)
OR self::replace($word, 'fulness', 'ful', 0)
OR self::replace($word, 'ousness', 'ous', 0)
OR self::replace($word, 'alism', 'al', 0);
break;
case 't':
self::replace($word, 'biliti', 'ble', 0)
OR self::replace($word, 'aliti', 'al', 0)
OR self::replace($word, 'iviti', 'ive', 0);
break;
}
return $word;
}
/**
* Step 3
*
* @param string $word String to stem
*/
private static function step3($word)
{
switch (substr($word, -2, 1)) {
case 'a':
self::replace($word, 'ical', 'ic', 0);
break;
case 's':
self::replace($word, 'ness', '', 0);
break;
case 't':
self::replace($word, 'icate', 'ic', 0)
OR self::replace($word, 'iciti', 'ic', 0);
break;
case 'u':
self::replace($word, 'ful', '', 0);
break;
case 'v':
self::replace($word, 'ative', '', 0);
break;
case 'z':
self::replace($word, 'alize', 'al', 0);
break;
}
return $word;
}
/**
* Step 4
*
* @param string $word Word to stem
*/
private static function step4($word)
{
switch (substr($word, -2, 1)) {
case 'a':
self::replace($word, 'al', '', 1);
break;
case 'c':
self::replace($word, 'ance', '', 1)
OR self::replace($word, 'ence', '', 1);
break;
case 'e':
self::replace($word, 'er', '', 1);
break;
case 'i':
self::replace($word, 'ic', '', 1);
break;
case 'l':
self::replace($word, 'able', '', 1)
OR self::replace($word, 'ible', '', 1);
break;
case 'n':
self::replace($word, 'ant', '', 1)
OR self::replace($word, 'ement', '', 1)
OR self::replace($word, 'ment', '', 1)
OR self::replace($word, 'ent', '', 1);
break;
case 'o':
if (substr($word, -4) == 'tion' OR substr($word, -4) == 'sion') {
self::replace($word, 'ion', '', 1);
} else {
self::replace($word, 'ou', '', 1);
}
break;
case 's':
self::replace($word, 'ism', '', 1);
break;
case 't':
self::replace($word, 'ate', '', 1)
OR self::replace($word, 'iti', '', 1);
break;
case 'u':
self::replace($word, 'ous', '', 1);
break;
case 'v':
self::replace($word, 'ive', '', 1);
break;
case 'z':
self::replace($word, 'ize', '', 1);
break;
}
return $word;
}
/**
* Step 5
*
* @param string $word Word to stem
*/
private static function step5($word)
{
// Part a
if (substr($word, -1) == 'e') {
if (self::m(substr($word, 0, -1)) > 1) {
self::replace($word, 'e', '');
} else if (self::m(substr($word, 0, -1)) == 1) {
if (!self::cvc(substr($word, 0, -1))) {
self::replace($word, 'e', '');
}
}
}
// Part b
if (self::m($word) > 1 AND self::doubleConsonant($word) AND substr($word, -1) == 'l') {
$word = substr($word, 0, -1);
}
return $word;
}
/**
* Replaces the first string with the second, at the end of the string. If third
* arg is given, then the preceding string must match that m count at least.
*
* @param string $str String to check
* @param string $check Ending to check for
* @param string $repl Replacement string
* @param int $m Optional minimum number of m() to meet
* @return bool Whether the $check string was at the end
* of the $str string. True does not necessarily mean
* that it was replaced.
*/
private static function replace(&$str, $check, $repl, $m = null)
{
$len = 0 - strlen($check);
if (substr($str, $len) == $check) {
$substr = substr($str, 0, $len);
if (is_null($m) OR self::m($substr) > $m) {
$str = $substr . $repl;
}
return true;
}
return false;
}
/**
* What, you mean it's not obvious from the name?
*
* m() measures the number of consonant sequences in $str. if c is
* a consonant sequence and v a vowel sequence, and <..> indicates arbitrary
* presence,
*
* <c><v> gives 0
* <c>vc<v> gives 1
* <c>vcvc<v> gives 2
* <c>vcvcvc<v> gives 3
*
* @param string $str The string to return the m count for
* @return int The m count
*/
private static function m($str)
{
$c = self::$regex_consonant;
$v = self::$regex_vowel;
$str = preg_replace("#^$c+#", '', $str);
$str = preg_replace("#$v+$#", '', $str);
preg_match_all("#($v+$c+)#", $str, $matches);
return count($matches[1]);
}
/**
* Returns true/false as to whether the given string contains two
* of the same consonant next to each other at the end of the string.
*
* @param string $str String to check
* @return bool Result
*/
private static function doubleConsonant($str)
{
$c = self::$regex_consonant;
return preg_match("#$c{2}$#", $str, $matches) AND $matches[0]{0} == $matches[0]{1};
}
/**
* Checks for ending CVC sequence where second C is not W, X or Y
*
* @param string $str String to check
* @return bool Result
*/
private static function cvc($str)
{
$c = self::$regex_consonant;
$v = self::$regex_vowel;
return preg_match("#($c$v$c)$#", $str, $matches)
AND strlen($matches[1]) == 3
AND $matches[1]{2} != 'w'
AND $matches[1]{2} != 'x'
AND $matches[1]{2} != 'y';
}
}
?>