Suomenkielinen Porter stemmer

suomi_stemmer.php

<?php

add_filter( 'relevanssi_stemmer', 'suomi_stemmer' );
function suomi_stemmer( $merkkijono ) {
    $stemmer = new FinnishStemmer();
    return $stemmer->process( $merkkijono );
}

class FinnishStemmer {

    private static $vowels = array("a", "e", "i", "o", "u", "y", "å", "ä", "ö");
    private static $long_vowels = array("aa", "ee", "ii", "oo", "uu", "yy", "åå", "ää", "öö");
    private static $consonants = array("b", "c", "d", "f", "g", "h", "j", "k", "l", "m", "n", "p", "q", "r", "s", "t", "v", "w", "x", "z");

    protected $word;
    protected $r1;
    protected $r2;
    protected $removed_in_step_3;

    private function find_r($in) {
        $word_vowels = array();
        for ($i = 0; $i < mb_strlen($in); $i++) {
            $letter = mb_substr($in, $i, 1);
            if (in_array($letter, static::$vowels)) $word_vowels[] = $i;
        }

        $index = mb_strlen($in);
        $value = "";

        foreach ($word_vowels as $pos) {
            $after = $pos + 1;
            $letter = mb_substr($in, $after, 1);
            if (!in_array($letter, static::$vowels)) {
                $index = $after + 1;
                $value = mb_substr($in, $after + 1);
                break;
            }
        }

        return array($index, $value);
    }

    private function is_suffix($suffix, $in, $preceeded = "", $negative_preceeded = "") {
        $length = mb_strlen($suffix) * -1;
        if (mb_substr($in, $length) == $suffix) {
            if (is_array($preceeded)) {
                foreach($preceeded as $preceed_candidate) {
                    $candidate_length = mb_strlen($preceed_candidate);
                    $preceeding_letter = mb_substr($this->word, $length - $candidate_length, $candidate_length);
                    if ($preceeding_letter == $preceed_candidate) {
                        return true;
                    }
                }
            } else if (is_array($negative_preceeded)) {
                foreach($negative_preceeded as $preceed_candidate) {
                    $candidate_length = mb_strlen($preceed_candidate);
                    $preceeding_letter = mb_substr($this->word, $length - $candidate_length, $candidate_length);
                    if ($preceeding_letter != $preceed_candidate) {
                        return true;
                    }
                }
            } else {
                return true;
            }
        } 
        return false;
    }

    private function is_suffix_cv($suffix, $in) {
        $length = mb_strlen($suffix) * -1;
        if (mb_substr($in, $length) == $suffix) {
            $preceeding_letter = mb_substr($this->word, $length, 1);
            if (in_array($preceeding_letter, static::$vowels)) {
                $preceeding_letter = mb_substr($this->word, $length - 1, 1);
                if (in_array($preceeding_letter, static::$consonants)) {
                    return true;
                }
            }
        }
        return false;
    }

    private function remove_suffix($suffix) {
        $this->word = mb_substr($this->word, 0, mb_strlen($suffix) * -1);
        $this->r1 = mb_substr($this->r1, 0, mb_strlen($suffix) * -1);
        $this->r2 = mb_substr($this->r2, 0, mb_strlen($suffix) * -1);
    }

    function step_1() {
        $r1 = $this->r1;
        $r2 = $this->r2;

        $preceeded = array_merge(static::$vowels, array('n', 't'));
        if ($this->is_suffix("kin", $r1, $preceeded)) {
            $this->remove_suffix("kin");
            return true;
        }

        if ($this->is_suffix("kaan", $r1, $preceeded)) {
            $this->remove_suffix("kaan");
            return true;
        }

        if ($this->is_suffix("kään", $r1, $preceeded)) {
            $this->remove_suffix("kään");
            return true;
        }

        if ($this->is_suffix("han", $r1, $preceeded)) {
            $this->remove_suffix("han");
            return true;
        }

        if ($this->is_suffix("hän", $r1, $preceeded)) {
            $this->remove_suffix("hän");
            return true;
        }

        if ($this->is_suffix("ko", $r1, $preceeded)) {
            $this->remove_suffix("ko");
            return true;
        }

        if ($this->is_suffix("kö", $r1, $preceeded)) {
            $this->remove_suffix("kö");
            return true;
        }

        if ($this->is_suffix("pa", $r1, $preceeded)) {
            $this->remove_suffix("pa");
            return true;
        }

        if ($this->is_suffix("pä", $r1, $preceeded)) {
            $this->remove_suffix("pä");
            return true;
        }

        if ($this->is_suffix("sti", $r2)) {
            $this->remove_suffix("sti");
            return true;
        }

        return false;
    }

    function step_2() {
        $r1 = $this->r1;
        $negative_preceeded = array('k');
        if ($this->is_suffix("si", $r1, false, $negative_preceeded)) {
            $this->remove_suffix("si");
            return true;
        }

        if ($this->is_suffix("ni", $r1)) {
            $this->remove_suffix("ni");
            return true;
        }
            
        if ($this->is_suffix("nsa", $r1)) {
            $this->remove_suffix("nsa");
            return true;
        }

        if ($this->is_suffix("nsä", $r1)) {
            $this->remove_suffix("nsä");
            return true;
        }

        if ($this->is_suffix("mme", $r1)) {
            $this->remove_suffix("mme");
            return true;
        }

        if ($this->is_suffix("nne", $r1)) {
            $this->remove_suffix("nne");
            return true;
        }

        return false;
    }

    private function step_3() {
        $r1 = $this->r1;
        $r2 = $this->r2;

        $preceeded = array('a');
        if ($this->is_suffix("han", $r1, $preceeded)) {
            $this->remove_suffix("han");
            return true;
        }

        $preceeded = array('e');
        if ($this->is_suffix("hen", $r1, $preceeded)) {
            $this->remove_suffix("hen");
            return true;
        }

        $preceeded = array('i');
        if ($this->is_suffix("hin", $r1, $preceeded)) {
            $this->remove_suffix("hin");
            return true;
        }

        $preceeded = array('o');
        if ($this->is_suffix("hon", $r1, $preceeded)) {
            $this->remove_suffix("hon");
            return true;
        }

        $preceeded = array('y');
        if ($this->is_suffix("hyn", $r1, $preceeded)) {
            $this->remove_suffix("hyn");
            return true;
        }

        $preceeded = array('ä');
        if ($this->is_suffix("hän", $r1, $preceeded)) {
            $this->remove_suffix("hän");
            return true;
        }

        $preceeded = array('ö');
        if ($this->is_suffix("hön", $r1, $preceeded)) {
            $this->remove_suffix("hön");
            return true;
        }

        $preceeded = array('ai', 'ei', 'ii', 'oi', 'ui', 'yi', 'äi', 'öi');
        if ($this->is_suffix("siin", $r1, $preceeded)) {
            $this->remove_suffix("siin");
            return true;
        }
        
        $preceeded = array('ai', 'ei', 'ii', 'oi', 'ui', 'yi', 'äi', 'öi');
        if ($this->is_suffix("den", $r1, $preceeded)) {
            $this->remove_suffix("den");
            return true;
        }

        $preceeded = array('ai', 'ei', 'ii', 'oi', 'ui', 'yi', 'äi', 'öi');
        if ($this->is_suffix("tten", $r1, $preceeded)) {
            $this->remove_suffix("tten");
            return true;
        }

        $preceeded = static::$long_vowels;
        if ($this->is_suffix("seen", $r1, $preceeded)) {
            $this->remove_suffix("seen");
            return true;
        }

        $preceeded = array('e');
        if ($this->is_suffix("tta", $r1, $preceeded)) {
            $this->remove_suffix("tta");
            return true;
        }
        if ($this->is_suffix("ttä", $r1, $preceeded)) {
            $this->remove_suffix("ttä");
            return true;
        }

        if ($this->is_suffix("sta", $r1)) {
            $this->remove_suffix("sta");
            return true;
        }
        if ($this->is_suffix("ssa", $r1)) {
            $this->remove_suffix("ssa");
            return true;
        }
        if ($this->is_suffix("stä", $r1)) {
            $this->remove_suffix("stä");
            return true;
        }
        if ($this->is_suffix("lta", $r1)) {
            $this->remove_suffix("lta");
            return true;
        }
        if ($this->is_suffix("ltä", $r1)) {
            $this->remove_suffix("ltä");
            return true;
        }
        if ($this->is_suffix("lla", $r1)) {
            $this->remove_suffix("lla");
            return true;
        }
        if ($this->is_suffix("llä", $r1)) {
            $this->remove_suffix("llä");
            return true;
        }
        if ($this->is_suffix("lle", $r1)) {
            $this->remove_suffix("lle");
            return true;
        }
        if ($this->is_suffix("ksi", $r1)) {
            $this->remove_suffix("ksi");
            return true;
        }
        if ($this->is_suffix("ine", $r1)) {
            $this->remove_suffix("ine");
            return true;
        }
        if ($this->is_suffix("ta", $r1)) {
            $this->remove_suffix("ta");
            return true;
        }
        if ($this->is_suffix("tä", $r1)) {
            $this->remove_suffix("tä");
            return true;
        }
        if ($this->is_suffix("na", $r1)) {
            $this->remove_suffix("na");
            return true;
        }
        if ($this->is_suffix("nä", $r1)) {
            $this->remove_suffix("nä");
            return true;
        }
        if ($this->is_suffix("n", $r1)) {
            $this->remove_suffix("n");
            $preceeding = array_merge(static::$long_vowels, array('ie'));
            if (in_array(mb_substr($this->word, -2), $preceeding)) {
                $this->remove_suffix("n");
            }
            return true;
        }

        if ($this->is_suffix_cv("a", $r1)) {
            $this->remove_suffix("a");
            return true;
        }

        return false;
    }

    private function step_4() {
        $r2 = $this->r2;

        $negative_preceeded = array('po');
        if ($this->is_suffix("mpi", $r2, false, $negative_preceeded)) {
            $this->remove_suffix("mpi");
            return true;
        }
        if ($this->is_suffix("mpa", $r2, false, $negative_preceeded)) {
            $this->remove_suffix("mpa");
            return true;
        }
        if ($this->is_suffix("mpä", $r2, false, $negative_preceeded)) {
            $this->remove_suffix("mpä");
            return true;
        }
        if ($this->is_suffix("mmi", $r2, false, $negative_preceeded)) {
            $this->remove_suffix("mmi");
            return true;
        }
        if ($this->is_suffix("mma", $r2, false, $negative_preceeded)) {
            $this->remove_suffix("mma");
            return true;
        }
        if ($this->is_suffix("mmä", $r2, false, $negative_preceeded)) {
            $this->remove_suffix("mmä");
            return true;
        }

        if ($this->is_suffix("impi", $r2)) {
            $this->remove_suffix("impi");
            return true;
        }
        if ($this->is_suffix("impa", $r2)) {
            $this->remove_suffix("impa");
            return true;
        }
        if ($this->is_suffix("impä", $r2)) {
            $this->remove_suffix("impä");
            return true;
        }
        if ($this->is_suffix("immi", $r2)) {
            $this->remove_suffix("immi");
            return true;
        }
        if ($this->is_suffix("imma", $r2)) {
            $this->remove_suffix("imma");
            return true;
        }
        if ($this->is_suffix("immä", $r2)) {
            $this->remove_suffix("immä");
            return true;
        }
        if ($this->is_suffix("eja", $r2)) {
            $this->remove_suffix("eja");
            return true;
        }
        if ($this->is_suffix("ejä", $r2)) {
            $this->remove_suffix("ejä");
            return true;
        }
    }

    private function step_5() {
        $r1 = $this->r1;
        $r2 = $this->r2;
        
        if ($this->removed_in_step_3) {
            if ($this->is_suffix("i", $r1)) {
                $this->remove_suffix("i");
                return true;
            }
            if ($this->is_suffix("j", $r1)) {
                $this->remove_suffix("j");
                return true;
            }
        }
        else {
            $preceeded = static::$vowels;
            if ($this->is_suffix("t", $r1, $preceeded)) {
                $this->remove_suffix("t");
                if ($this->is_suffix("imma", $r2)) {
                    $this->remove_suffix("imma");
                }
                $negative_preceeded = array('po');
                if ($this->is_suffix("mma", $r2, false, $negative_preceeded)) {
                    $this->remove_suffix("mma");
                }
                return true;
            }

        }
    }

    private function step_6() {
        $ending = mb_substr($this->r1, -2);
        if (in_array($ending, static::$long_vowels)) {
            $this->word = mb_substr($this->word, 0, -1);
            $this->r1 = mb_substr($this->r1, 0, -1);
            $this->r2 = mb_substr($this->r2, 0, -1);
        }

        $last = mb_substr($this->r1, -1);
        if (in_array($last, array('a', 'e', 'i', 'ä'))) {
            $second_to_last = mb_substr($this->r1, -2, 1);
            if (in_array($second_to_last, static::$consonants)) {
                $this->word = mb_substr($this->word, 0, -1);
                $this->r1 = mb_substr($this->r1, 0, -1);
                $this->r2 = mb_substr($this->r2, 0, -1);
            }
        }

        $ending = mb_substr($this->r1, -2);
        if (in_array($ending, array('oj', 'uj'))) {
            $this->word = mb_substr($this->word, 0, -1);
            $this->r1 = mb_substr($this->r1, 0, -1);
            $this->r2 = mb_substr($this->r2, 0, -1);
        }

        $ending = mb_substr($this->r1, -2);
        if (in_array($ending, array('jo'))) {
            $this->word = mb_substr($this->word, 0, -1);
            $this->r1 = mb_substr($this->r1, 0, -1);
            $this->r2 = mb_substr($this->r2, 0, -1);
        }

        $last_consonant_found = false;
        for ($i = mb_strlen($this->word); $i > 0; $i--) {
            $letter = mb_substr($this->word, $i, 1);
            if (in_array($letter, static::$consonants)) {
                $prev_letter = mb_substr($this->word, $i - 1, 1);
                if ($prev_letter == $letter) {
                    $this->word = mb_substr($this->word, 0, $i - 1) . mb_substr($this->word, $i);
                    break;
                }
                else {
                    break;
                }
            }

        }
    }

    private function r1r2() {
        list($r1_index, $this->r1) = $this->find_r($this->word);
        if ($this->r1) {
            list($r2_index, $this->r2) = $this->find_r($this->r1);
        }
    }

    function process($word) {
        $this->word = $word;
        $this->r1r2();

        $this->step_1();
        $this->step_2();
        
        $removed = $this->step_3();
        $this->removed_in_step_3 = $removed;

        $this->step_4();
        $this->step_5();
        $this->step_6();
        ;
        return $this->word;
    }
}