class Porter2 in Porter-Stemmer 8
PHP Implementation of the Porter2 Stemming Algorithm.
See http://snowball.tartarus.org/algorithms/english/stemmer.html .
Hierarchy
- class \Drupal\porterstemmer\Porter2
Expanded class hierarchy of Porter2
7 files declare their use of Porter2
- Porter2Test1.php in tests/
src/ Unit/ Porter2Test1.php - Porter2Test2.php in tests/
src/ Unit/ Porter2Test2.php - Porter2Test3.php in tests/
src/ Unit/ Porter2Test3.php - Porter2Test4.php in tests/
src/ Unit/ Porter2Test4.php - Porter2Test5.php in tests/
src/ Unit/ Porter2Test5.php
File
- src/
Porter2.php, line 10
Namespace
Drupal\porterstemmerView source
class Porter2 {
/**
* Computes the stem of the word.
*
* @return string
* The word's stem.
*/
public static function stem($word) {
$exceptions = [
'skis' => 'ski',
'skies' => 'sky',
'dying' => 'die',
'lying' => 'lie',
'tying' => 'tie',
'idly' => 'idl',
'gently' => 'gentl',
'ugly' => 'ugli',
'early' => 'earli',
'only' => 'onli',
'singly' => 'singl',
'sky' => 'sky',
'news' => 'news',
'howe' => 'howe',
'atlas' => 'atlas',
'cosmos' => 'cosmos',
'bias' => 'bias',
'andes' => 'andes',
];
// Process exceptions.
if (isset($exceptions[$word])) {
$word = $exceptions[$word];
}
elseif (strlen($word) > 2) {
// Only execute algorithm on words that are longer than two letters.
$word = self::prepare($word);
$word = self::step0($word);
$word = self::step1a($word);
$word = self::step1b($word);
$word = self::step1c($word);
$word = self::step2($word);
$word = self::step3($word);
$word = self::step4($word);
$word = self::step5($word);
}
return strtolower($word);
}
/**
* Set initial y, or y after a vowel, to Y.
*
* @param string $word
* The word to stem.
*
* @return string
* The prepared word.
*/
protected static function prepare($word) {
$inc = 0;
if (strpos($word, "'") === 0) {
$word = substr($word, 1);
}
while ($inc <= strlen($word)) {
if (substr($word, $inc, 1) === 'y' && ($inc == 0 || self::isVowel($inc - 1, $word))) {
$word = substr_replace($word, 'Y', $inc, 1);
}
$inc++;
}
return $word;
}
/**
* Search for the longest among the "s" suffixes and removes it.
*
* @param string $word
* The word to stem.
*
* @return string
* The modified word.
*/
protected static function step0($word) {
$found = FALSE;
$checks = [
"'s'",
"'s",
"'",
];
foreach ($checks as $check) {
if (!$found && self::hasEnding($word, $check)) {
$word = self::removeEnding($word, $check);
$found = TRUE;
}
}
return $word;
}
/**
* Handles various suffixes, of which the longest is replaced.
*
* @param string $word
* The word to stem.
*
* @return string
* The modified word.
*/
protected static function step1a($word) {
$found = FALSE;
if (self::hasEnding($word, 'sses')) {
$word = self::removeEnding($word, 'sses') . 'ss';
$found = TRUE;
}
$checks = [
'ied',
'ies',
];
foreach ($checks as $check) {
if (!$found && self::hasEnding($word, $check)) {
// @todo: check order here.
$length = strlen($word);
$word = self::removeEnding($word, $check);
if ($length > 4) {
$word .= 'i';
}
else {
$word .= 'ie';
}
$found = TRUE;
}
}
if (self::hasEnding($word, 'us') || self::hasEnding($word, 'ss')) {
$found = TRUE;
}
// Delete if preceding word part has a vowel not immediately before the s.
if (!$found && self::hasEnding($word, 's') && self::containsVowel(substr($word, 0, -2))) {
$word = self::removeEnding($word, 's');
}
return $word;
}
/**
* Handles various suffixes, of which the longest is replaced.
*
* @param string $word
* The word to stem.
*
* @return string
* The modified word.
*/
protected static function step1b($word) {
$exceptions = [
'inning',
'outing',
'canning',
'herring',
'earring',
'proceed',
'exceed',
'succeed',
];
if (in_array($word, $exceptions)) {
return $word;
}
$checks = [
'eedly',
'eed',
];
foreach ($checks as $check) {
if (self::hasEnding($word, $check)) {
if (self::r($word, 1) !== strlen($word)) {
$word = self::removeEnding($word, $check) . 'ee';
}
return $word;
}
}
$checks = [
'ingly',
'edly',
'ing',
'ed',
];
$second_endings = [
'at',
'bl',
'iz',
];
foreach ($checks as $check) {
// If the ending is present and the previous part contains a vowel.
if (self::hasEnding($word, $check) && self::containsVowel(substr($word, 0, -strlen($check)))) {
$word = self::removeEnding($word, $check);
foreach ($second_endings as $ending) {
if (self::hasEnding($word, $ending)) {
return $word . 'e';
}
}
// If the word ends with a double, remove the last letter.
$double_removed = self::removeDoubles($word);
if ($double_removed != $word) {
$word = $double_removed;
}
elseif (self::isShort($word)) {
// If the word is short, add e (so hop -> hope).
$word .= 'e';
}
return $word;
}
}
return $word;
}
/**
* Replaces suffix y or Y with i if after non-vowel not @ word begin.
*
* @param string $word
* The word to stem.
*
* @return string
* The modified word.
*/
protected static function step1c($word) {
if ((self::hasEnding($word, 'y') || self::hasEnding($word, 'Y')) && strlen($word) > 2 && !self::isVowel(strlen($word) - 2, $word)) {
$word = self::removeEnding($word, 'y');
$word .= 'i';
}
return $word;
}
/**
* Implements step 2 of the Porter2 algorithm.
*
* @param string $word
* The word to stem.
*
* @return string
* The modified word.
*/
protected static function step2($word) {
$checks = [
"ization" => "ize",
"iveness" => "ive",
"fulness" => "ful",
"ational" => "ate",
"ousness" => "ous",
"biliti" => "ble",
"tional" => "tion",
"lessli" => "less",
"fulli" => "ful",
"entli" => "ent",
"ation" => "ate",
"aliti" => "al",
"iviti" => "ive",
"ousli" => "ous",
"alism" => "al",
"abli" => "able",
"anci" => "ance",
"alli" => "al",
"izer" => "ize",
"enci" => "ence",
"ator" => "ate",
"bli" => "ble",
"ogi" => "og",
];
foreach ($checks as $find => $replace) {
if (self::hasEnding($word, $find)) {
if (self::inR1($word, $find)) {
$word = self::removeEnding($word, $find) . $replace;
}
return $word;
}
}
if (self::hasEnding($word, 'li')) {
if (strlen($word) > 4 && self::validLi(self::charAt(-3, $word))) {
$word = self::removeEnding($word, 'li');
}
}
return $word;
}
/**
* Implements step 3 of the Porter2 algorithm.
*
* @param string $word
* The word to stem.
*
* @return string
* The modified word.
*/
protected static function step3($word) {
$checks = [
'ational' => 'ate',
'tional' => 'tion',
'alize' => 'al',
'icate' => 'ic',
'iciti' => 'ic',
'ical' => 'ic',
'ness' => '',
'ful' => '',
];
foreach ($checks as $find => $replace) {
if (self::hasEnding($word, $find)) {
if (self::inR1($word, $find)) {
$word = self::removeEnding($word, $find) . $replace;
}
return $word;
}
}
if (self::hasEnding($word, 'ative')) {
if (self::inR2($word, 'ative')) {
$word = self::removeEnding($word, 'ative');
}
}
return $word;
}
/**
* Implements step 4 of the Porter2 algorithm.
*
* @param string $word
* The word to stem.
*
* @return string
* The modified word.
*/
protected static function step4($word) {
$checks = [
'ement',
'ment',
'ance',
'ence',
'able',
'ible',
'ant',
'ent',
'ion',
'ism',
'ate',
'iti',
'ous',
'ive',
'ize',
'al',
'er',
'ic',
];
foreach ($checks as $check) {
// Among the suffixes, if found and in R2, delete.
if (self::hasEnding($word, $check)) {
if (self::inR2($word, $check)) {
if ($check !== 'ion' || in_array(self::charAt(-4, $word), [
's',
't',
])) {
$word = self::removeEnding($word, $check);
}
}
return $word;
}
}
return $word;
}
/**
* Implements step 5 of the Porter2 algorithm.
*
* @param string $word
* The word to stem.
*
* @return string
* The modified word.
*/
protected static function step5($word) {
if (self::hasEnding($word, 'e')) {
// Delete if in R2, or in R1 and not preceded by a short syllable.
if (self::inR2($word, 'e') || self::inR1($word, 'e') && !self::isShortSyllable($word, strlen($word) - 3)) {
$word = self::removeEnding($word, 'e');
}
return $word;
}
if (self::hasEnding($word, 'l')) {
// Delete if in R2 and preceded by l.
if (self::inR2($word, 'l') && self::charAt(-2, $word) == 'l') {
$word = self::removeEnding($word, 'l');
}
}
return $word;
}
/**
* Removes certain double consonants from the word's end.
*
* @param string $word
* The word to stem.
*
* @return string
* The modified word.
*/
protected static function removeDoubles($word) {
$doubles = [
'bb',
'dd',
'ff',
'gg',
'mm',
'nn',
'pp',
'rr',
'tt',
];
foreach ($doubles as $double) {
if (substr($word, -2) == $double) {
$word = substr($word, 0, -1);
break;
}
}
return $word;
}
/**
* Checks whether a character is a vowel.
*
* @param int $position
* The character's position.
* @param string $word
* The word in which to check.
* @param string[] $additional
* (optional) Additional characters that should count as vowels.
*
* @return bool
* TRUE if the character is a vowel, FALSE otherwise.
*/
protected static function isVowel($position, $word, array $additional = []) {
$vowels = array_merge([
'a',
'e',
'i',
'o',
'u',
'y',
], $additional);
return in_array(self::charAt($position, $word), $vowels);
}
/**
* Retrieves the character at the given position.
*
* @param int $position
* The 0-based index of the character. If a negative number is given, the
* position is counted from the end of the string.
* @param string $word
* The word from which to retrieve the character.
*
* @return string
* The character at the given position, or an empty string if the given
* position was illegal.
*/
protected static function charAt($position, $word) {
$length = strlen($word);
if (abs($position) >= $length) {
return '';
}
if ($position < 0) {
$position += $length;
}
return $word[$position];
}
/**
* Determines whether the word ends in a "vowel-consonant" suffix.
*
* Unless the word is only two characters long, it also checks that the
* third-last character is neither "w", "x" nor "Y".
*
* @param string $word
* The word to check.
* @param int|null $position
* (optional) If given, do not check the end of the word, but the character
* at the given position, and the next one.
*
* @return bool
* TRUE if the word has the described suffix, FALSE otherwise.
*/
protected static function isShortSyllable($word, $position = NULL) {
if ($position === NULL) {
$position = strlen($word) - 2;
}
// A vowel at the beginning of the word followed by a non-vowel.
if ($position === 0) {
return self::isVowel(0, $word) && !self::isVowel(1, $word);
}
// Vowel followed by non-vowel other than w, x, Y and preceded by
// non-vowel.
$additional = [
'w',
'x',
'Y',
];
return !self::isVowel($position - 1, $word) && self::isVowel($position, $word) && !self::isVowel($position + 1, $word, $additional);
}
/**
* Determines whether the word is short.
*
* A word is called short if it ends in a short syllable and if R1 is null.
*
* @param string $word
* The word to check.
*
* @return bool
* TRUE if the word is short, FALSE otherwise.
*/
protected static function isShort($word) {
return self::isShortSyllable($word) && self::r($word, 1) == strlen($word);
}
/**
* Determines the start of a certain "R" region.
*
* R is a region after the first non-vowel following a vowel, or end of word.
*
* @param string $word
* The word to check.
* @param int $type
* (optional) 1 or 2. If 2, then calculate the R after the R1.
*
* @return int
* The R position.
*/
protected static function r($word, $type = 1) {
$inc = 1;
if ($type === 2) {
$inc = self::r($word, 1);
}
elseif (strlen($word) > 5) {
$prefix_5 = substr($word, 0, 5);
if ($prefix_5 === 'gener' || $prefix_5 === 'arsen') {
return 5;
}
if (strlen($word) > 5 && substr($word, 0, 6) === 'commun') {
return 6;
}
}
while ($inc <= strlen($word)) {
if (!self::isVowel($inc, $word) && self::isVowel($inc - 1, $word)) {
$position = $inc;
break;
}
$inc++;
}
if (!isset($position)) {
$position = strlen($word);
}
else {
// We add one, as this is the position AFTER the first non-vowel.
$position++;
}
return $position;
}
/**
* Checks whether the given string is contained in R1.
*
* @param string $word
* The word to check.
* @param string $string
* The string.
*
* @return bool
* TRUE if the string is in R1 in the word, FALSE otherwise.
*/
protected static function inR1($word, $string) {
$r1 = substr($word, self::r($word, 1));
return strpos($r1, $string) !== FALSE;
}
/**
* Checks whether the given string is contained in R2.
*
* @param string $word
* The word to check.
* @param string $string
* The string.
*
* @return bool
* TRUE if the string is in R2 in the word, FALSE otherwise.
*/
protected static function inR2($word, $string) {
$r2 = substr($word, self::r($word, 2));
return strpos($r2, $string) !== FALSE;
}
/**
* Checks whether the word ends with the given string.
*
* @param string $word
* The word to check.
* @param string $string
* The string.
*
* @return bool
* TRUE if the word ends with the given string, FALSE otherwise.
*/
protected static function hasEnding($word, $string) {
$length = strlen($string);
if ($length > strlen($word)) {
return FALSE;
}
return substr_compare($word, $string, -1 * $length, $length) === 0;
}
/**
* Removes a given string from the end of the current word.
*
* Does not check whether the ending is actually there.
*
* @param string $word
* The word to check.
* @param string $string
* The ending to remove.
*
* @return string
* The word without the given ending.
*/
protected static function removeEnding($word, $string) {
return substr($word, 0, -strlen($string));
}
/**
* Checks whether the given string contains a vowel.
*
* @param string $string
* The string to check.
*
* @return bool
* TRUE if the string contains a vowel, FALSE otherwise.
*/
protected static function containsVowel($string) {
$inc = 0;
$return = FALSE;
while ($inc < strlen($string)) {
if (self::isVowel($inc, $string)) {
$return = TRUE;
break;
}
$inc++;
}
return $return;
}
/**
* Checks whether the given string is a valid -li prefix.
*
* @param string $string
* The string to check.
*
* @return bool
* TRUE if the given string is a valid -li prefix, FALSE otherwise.
*/
protected static function validLi($string) {
return in_array($string, [
'c',
'd',
'e',
'g',
'h',
'k',
'm',
'n',
'r',
't',
]);
}
}Members
Name |
Modifiers | Type | Description | Overrides |
|---|---|---|---|---|
|
Porter2:: |
protected static | function | Retrieves the character at the given position. | |
|
Porter2:: |
protected static | function | Checks whether the given string contains a vowel. | |
|
Porter2:: |
protected static | function | Checks whether the word ends with the given string. | |
|
Porter2:: |
protected static | function | Checks whether the given string is contained in R1. | |
|
Porter2:: |
protected static | function | Checks whether the given string is contained in R2. | |
|
Porter2:: |
protected static | function | Determines whether the word is short. | |
|
Porter2:: |
protected static | function | Determines whether the word ends in a "vowel-consonant" suffix. | |
|
Porter2:: |
protected static | function | Checks whether a character is a vowel. | |
|
Porter2:: |
protected static | function | Set initial y, or y after a vowel, to Y. | |
|
Porter2:: |
protected static | function | Determines the start of a certain "R" region. | |
|
Porter2:: |
protected static | function | Removes certain double consonants from the word's end. | |
|
Porter2:: |
protected static | function | Removes a given string from the end of the current word. | |
|
Porter2:: |
public static | function | Computes the stem of the word. | |
|
Porter2:: |
protected static | function | Search for the longest among the "s" suffixes and removes it. | |
|
Porter2:: |
protected static | function | Handles various suffixes, of which the longest is replaced. | |
|
Porter2:: |
protected static | function | Handles various suffixes, of which the longest is replaced. | |
|
Porter2:: |
protected static | function | Replaces suffix y or Y with i if after non-vowel not @ word begin. | |
|
Porter2:: |
protected static | function | Implements step 2 of the Porter2 algorithm. | |
|
Porter2:: |
protected static | function | Implements step 3 of the Porter2 algorithm. | |
|
Porter2:: |
protected static | function | Implements step 4 of the Porter2 algorithm. | |
|
Porter2:: |
protected static | function | Implements step 5 of the Porter2 algorithm. | |
|
Porter2:: |
protected static | function | Checks whether the given string is a valid -li prefix. |