PHP ngram

ngram.php

<?php
class NGram
{
    /**
     * The length of the n-gram.
     *
     * @var int
     */
    protected $n;

    /**
     * @var string
     */
    protected $string;

    /**
     * NGram constructor.
     *
     * @param int    $n
     * @param string $string
     *
     * @throws \TextUtils\Exceptions\InvalidArgumentException
     */
    public function __construct(int $n, string $string)
    {
        $this->setN($n);
        $this->setString($string);
    }

    /**
     * Static wrapper for n-gram generator.
     *
     * @param string $text
     * @param int    $n
     *
     * @throws \TextUtils\Exceptions\InvalidArgumentException
     *
     * @return array
     */
    public static function for(string $text, int $n = 3)
    {
        return (new static($n, $text))->get();
    }

    /**
     * Static wrapper to generate a bigram.
     *
     * @param string $text
     *
     * @throws \TextUtils\Exceptions\InvalidArgumentException
     *
     * @return array
     */
    public static function bigram(string $text) : array
    {
        return self::for($text, 2);
    }

    /**
     * Static wrapper to generate a trigram.
     *
     * @param string $text
     *
     * @throws \TextUtils\Exceptions\InvalidArgumentException
     *
     * @return array
     */
    public static function trigram(string $text) : array
    {
        return self::for($text, 3);
    }

    /**
     * Generate the N-gram for the provided string.
     *
     * @return array
     */
    public function get() : array
    {
        $nGrams = [];

        $text = $this->getString();
        $max = mb_strlen($text);
        $n = $this->getN();
        for ($i = 0; $i + $n <= $max; $i++) {
            $partial = '';
            for ($j = 0; $j < $n; $j++) {
                $partial .= mb_substr($text, $j + $i,1); //$text[$j + $i];
            }
            $nGrams[] = $partial;
        }

        return $nGrams;
    }

    /**
     * @return int
     */
    public function getN() : int
    {
        return $this->n;
    }

    /**
     * Set the length of the n-gram.
     *
     * @param int $n
     *
     * @throws \TextUtils\Exceptions\InvalidArgumentException
     *
     * @return \TextUtils\NGram
     */
    public function setN(int $n) : NGram
    {
        if ($n < 1) {
            //throw new InvalidArgumentException('Provided number cannot be smaller than 1');
        }

        $this->n = $n;

        return $this;
    }

    /**
     * Set the string to create the n-gram for.
     *
     * @param string $string
     *
     * @return \TextUtils\NGram
     */
    public function setString(string $string) : NGram
    {
        $this->string = $string;

        return $this;
    }

    /**
     * Get the string used for the n-gram.
     *
     * @return string
     */
    public function getString() : string
    {
        return $this->string;
    }
}


/*
$n=new NGram(3,'электростанция');
print_r($n->trigram('электростанция'));*/

ngram.sql

DELIMITER ;;
DROP FUNCTION IF EXISTS `ngram`;;
CREATE FUNCTION `ngram`(`inStr` varchar(255), `n` tinyint(1)) RETURNS varchar(255) CHARSET utf8
BEGIN
    SET @counter = 1;
    SET @len = 1;
    SET @result = "";
    SET @len = CHAR_LENGTH(inStr);
 
    WHILE (@counter + (n-1)) <= @len  DO
      SET @ngram = "";
      SET @i = 0;
      WHILE @i < n DO
        SET @ngram = concat(@ngram, SUBSTRING(inStr,@counter+@i, 1));
        SET @i = @i+1;
      END WHILE;
      IF @result="" THEN
        SET @result = concat(@result, @ngram);
      ELSE 
        SET @result = concat(@result, "-", @ngram);
      END IF;

      SET @counter = @counter+1;
    END WHILE;
RETURN @result;
END;;
DELIMITER ;

ngrmFunction.php

<?php
function createNGram($n, $token)
{
    $nGrams  = array();
    $counter = 0;
    while (($counter + ($n - 1)) < mb_strlen($token)) {
        $nGram = "";
        for ($i = 0; $i < $n; $i++) {
            $nGram .= mb_substr($token, $counter + $i, 1);
            if ($i != $n - 1) {
                $nGram .= "";
            }
        }
        $nGrams[] = $nGram;
        $counter++;
    }
    return array_values($nGrams);
}
//print_r(createNGram(3,"электростанция"));

SELECT keyword
FROM terms
WHERE MATCH (trigrams) AGAINST ('сто-ток-ока-кан' );

SET GLOBAL log_bin_trust_function_creators = 1;