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<?php
declare(strict_types = 1);
namespace LanguageDetection;
use LanguageDetection\Tokenizer\TokenizerInterface;
use LanguageDetection\Tokenizer\WhitespaceTokenizer;
/**
* Class NgramParser
*
* @copyright Patrick Schur
* @license https://opensource.org/licenses/mit-license.html MIT
* @author Patrick Schur <patrick_schur@outlook.de>
* @package LanguageDetection
*/
abstract class NgramParser
{
/**
* @var int
*/
protected $minLength = 1;
/**
* @var int
*/
protected $maxLength = 3;
/**
* @var int
*/
protected $maxNgrams = 310;
/**
* @var TokenizerInterface
*/
protected $tokenizer = null;
/**
* @param int $minLength
* @throws \LengthException
*/
public function setMinLength(int $minLength)
{
if ($minLength <= 0 || $minLength >= $this->maxLength)
{
throw new \LengthException('$minLength must be greater than zero and less than $this->maxLength.');
}
$this->minLength = $minLength;
}
/**
* @param int $maxLength
* @throws \LengthException
*/
public function setMaxLength(int $maxLength)
{
if ($maxLength <= $this->minLength)
{
throw new \LengthException('$maxLength must be greater than $this->minLength.');
}
$this->maxLength = $maxLength;
}
/**
* @param int $maxNgrams
* @throws \LengthException
*/
public function setMaxNgrams(int $maxNgrams)
{
if ($maxNgrams <= 0)
{
throw new \LengthException('$maxNgrams must be greater than zero.');
}
$this->maxNgrams = $maxNgrams;
}
/**
* Sets the tokenizer
*
* @param TokenizerInterface $tokenizer
*/
public function setTokenizer(TokenizerInterface $tokenizer)
{
$this->tokenizer = $tokenizer;
}
/**
* @param string $str
* @return array
*/
private function tokenize(string $str)
{
if (null === $this->tokenizer)
{
$this->tokenizer = new WhitespaceTokenizer();
}
return $this->tokenizer->tokenize($str);
}
/**
* @param string $str
* @return array
*/
protected function getNgrams(string $str): array
{
$tokens = [];
foreach ($this->tokenize($str) as $word)
{
$l = \mb_strlen($word);
for ($i = $this->minLength; $i <= $this->maxLength; ++$i)
{
for ($j = 0; ($i + $j - 1) < $l; ++$j, ++$tmp)
{
$tmp = &$tokens[$i][\mb_substr($word, $j, $i)];
}
}
}
foreach ($tokens as $i => $token)
{
$sum = \array_sum($token);
foreach ($token as $j => $value)
{
$tokens[$i][$j] = $value / $sum;
}
}
if (!\count($tokens))
{
return [];
}
$tokens = \array_merge(...$tokens);
unset($tokens['_']);
\arsort($tokens, SORT_NUMERIC);
return \array_slice(
\array_keys($tokens),
0,
$this->maxNgrams
);
}
}
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