這是一個函數(shù)定位接收一個字符串作為參數(shù)（連同其他配置可選參數(shù)），并且定位該字符串中的所有關(guān)鍵字（出現(xiàn)最多的詞），返回一個數(shù)組或一個字符串由逗號分隔的關(guān)鍵字。

/**
 * Finds all of the keywords (words that appear most) on param $str 
 * and return them in order of most occurrences to less occurrences.
 * @param string $str The string to search for the keywords.
 * @param int $minWordLen[optional] The minimun length (number of chars) of a word to be considered a keyword.
 * @param int $minWordOccurrences[optional] The minimun number of times a word has to appear 
 * on param $str to be considered a keyword.
 * @param boolean $asArray[optional] Specifies if the function returns a string with the 
 * keywords separated by a comma ($asArray = false) or a keywords array ($asArray = true).
 * @return mixed A string with keywords separated with commas if param $asArray is true, 
 * an array with the keywords otherwise.
 */
function extract_keywords($str, $minWordLen = 3, $minWordOccurrences = 2, $asArray = false)
{
	function keyword_count_sort($first, $sec)
	{
		return $sec[1] - $first[1];
	}
	$str = preg_replace('/[^\\w0-9 ]/', ' ', $str);
	$str = trim(preg_replace('/\s+/', ' ', $str));
 
	$words = explode(' ', $str);
	$keywords = array();
	while(($c_word = array_shift($words)) !== null)
	{
		if(strlen($c_word) <= $minWordLen) continue;
 
		$c_word = strtolower($c_word);
		if(array_key_exists($c_word, $keywords)) $keywords[$c_word][1]++;
		else $keywords[$c_word] = array($c_word, 1);
	}
	usort($keywords, 'keyword_count_sort');
 
	$final_keywords = array();
	foreach($keywords as $keyword_det)
	{
		if($keyword_det[1] < $minWordOccurrences) break;
		array_push($final_keywords, $keyword_det[0]);
	}
	return $asArray ? $final_keywords : implode(', ', $final_keywords);
}
 
//How to use
 
//Basic lorem ipsum text to extract the keywords
$text = "
Lorem ipsum dolor sit amet, consectetur adipiscing elit. 
Curabitur eget ipsum ut lorem laoreet porta a non libero. 
Vivamus in tortor metus. Suspendisse potenti. Curabitur 
metus nisi, adipiscing eget placerat suscipit, suscipit 
vitae felis. Integer eu odio enim, sed dignissim lorem. 
In fringilla molestie justo, vitae varius risus lacinia ac. 
Nulla porttitor justo a lectus iaculis ut vestibulum magna 
egestas. Ut sed purus et nibh cursus fringilla at id purus.
";
//Echoes: lorem, suscipit, metus, fringilla, purus, justo, eget, vitae, ipsum, curabitur, adipiscing
echo extract_keywords($text);
						

 

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