请用php实现tf-idf算法

好的，以下是一个简单的 PHP 实现 TF-IDF 算法的示例代码：

<?php
// 定义文本数据
$documents = array(
    "The sun is shining",
    "The weather is sweet",
    "The sun is shining and the weather is sweet"
);

// 对文本进行分词处理
$words = array();
foreach ($documents as $document) {
    $words[] = explode(' ', strtolower($document));
}

// 统计词频
$wordCounts = array();
foreach ($words as $wordList) {
    foreach ($wordList as $word) {
        if (!isset($wordCounts[$word])) {
            $wordCounts[$word] = 0;
        }
        $wordCounts[$word]++;
    }
}

// 计算 TF-IDF 值
$tfidf = array();
$totalDocuments = count($documents);
foreach ($words as $documentIndex => $wordList) {
    foreach ($wordList as $word) {
        // 计算 TF 值
        $tf = $wordCounts[$word] / count($wordList);
        // 计算 IDF 值
        $df = 0;
        foreach ($words as $doc) {
            if (in_array($word, $doc)) {
                $df++;
            }
        }
        $idf = log($totalDocuments / $df);
        // 计算 TF-IDF 值
        $tfidf[$documentIndex][$word] = $tf * $idf;
    }
}

// 输出结果
foreach ($tfidf as $documentIndex => $values) {
    echo "Document " . ($documentIndex + 1) . ":<br>";
    foreach ($values as $word => $tfidfValue) {
        echo $word . " - " . $tfidfValue . "<br>";
    }
    echo "<br>";
}
?>

请注意，此示例代码只是一个简单的示例，实际应用中需要考虑更多的因素，如停用词、词干提取等。