public function _strtolower($string)
{
    $small = array('а','б','в','г','д','е','ё','ж','з','и','й',
                   'к','л','м','н','о','п','р','с','т','у','ф',
                   'х','ч','ц','ш','щ','ю','я','ы','ъ','ь',
                   'э','ә','і','ң','ғ','ү','ұ','қ','ө','һ',
				   'a','b','c','d','e','f','g','h','i',
				   'j','k','l','m','n','o','p','q','r',
				   's','t','u','v','w','x','y','z');
    $large = array('А','Б','В','Г','Д','Е','Ё','Ж','З','И','Й',
                   'К','Л','М','Н','О','П','Р','С','Т','У','Ф',
                   'Х','Ч','Ц','Ш','Щ','Ю','Я','Ы','Ъ','Ь',
                   'Э','Ә','І','Ң','Ғ','Ү','Ұ','Қ','Ө','Һ',
				   'A','B','C','D','E','F','G','H','I', 
				   'J','K','L','M','N','O','P','Q','R',
				   'S','T','U','V','W','X','Y','Z');
    return str_replace($large, $small, $string);  
}

public function analysis_keyword($string)
	{
		$keywords = preg_split("/[\s,]+/",$this->_strtolower($string));
		
		if ($result =$keywords )
		{			
			$result = array_unique($result);
			
			foreach ($result as $key => $keyword)
			{			
				if (!$this->check_stop_keyword($keyword))
				{
					unset($result[$key]);
				}
				else
				{
					$result[$key] = trim($keyword);
				}
			}
		}
		
		return $result;
	}