Question

我有两个PHP函数来计算两个文本之间的关系。他们都使用单词模型包，但check2（）更快。无论如何，这两个函数都给出了相同的结果。为什么？ check1（）使用一个包含所有单词的大字典数组 - 如单词包模型中所述。 check2（）不使用一个大数组，而是一个只包含一个文本的单词的数组。所以check2（）不应该工作，但它没有。为什么两个函数都给出相同的结果？

function check1($terms_in_article1, $terms_in_article2) {
    global $zeit_check1;
    $zeit_s = microtime(TRUE);
    $length1 = count($terms_in_article1); // number of words
    $length2 = count($terms_in_article2); // number of words
    $all_terms = array_merge($terms_in_article1, $terms_in_article2);
    $all_terms = array_unique($all_terms);
    foreach ($all_terms as $all_termsa) {
        $term_vector1[$all_termsa] = 0;
        $term_vector2[$all_termsa] = 0;
    }
    foreach ($terms_in_article1 as $terms_in_article1a) {
        $term_vector1[$terms_in_article1a]++;
    }
    foreach ($terms_in_article2 as $terms_in_article2a) {
        $term_vector2[$terms_in_article2a]++;
    }
    $score = 0;
    foreach ($all_terms as $all_termsa) {
        $score += $term_vector1[$all_termsa]*$term_vector2[$all_termsa];
    }
    $score = $score/($length1*$length2);
    $score *= 500; // for better readability
    $zeit_e = microtime(TRUE);
    $zeit_check1 += ($zeit_e-$zeit_s);
    return $score;
}
function check2($terms_in_article1, $terms_in_article2) {
    global $zeit_check2;
    $zeit_s = microtime(TRUE);
    $length1 = count($terms_in_article1); // number of words
    $length2 = count($terms_in_article2); // number of words
    $score_table = array();
    foreach($terms_in_article1 as $term){
        if(!isset($score_table[$term])) $score_table[$term] = 0;
        $score_table[$term] += 1;
    }
    $score_table2 = array();
    foreach($terms_in_article2 as $term){
        if(isset($score_table[$term])){
            if(!isset($score_table2[$term])) $score_table2[$term] = 0;
            $score_table2[$term] += 1;
        }
    }
    $score = 0;
    foreach($score_table2 as $key => $entry){
        $score += $score_table[$key] * $entry;
    }
    $score = $score/($length1*$length2);
    $score *= 500;
    $zeit_e = microtime(TRUE);
    $zeit_check2 += ($zeit_e-$zeit_s);
    return $score;
}

我希望你能帮助我。提前谢谢！

Answer 1

因为您似乎关注性能，所以这里是check2函数中的算法的优化版本，它使用一些更多的内置函数来提高速度。

function check ($terms1, $terms2)
{
    $counts1 = array_count_values($terms1);
    $totalScore = 0;
    foreach ($terms2 as $term) {
        if (isset($counts1[$term])) $totalScore += $counts1[$term];
    }
    return $totalScore * 500 / (count($terms1) * count($terms2));
}

Answer 2

这两个函数实现了几乎相同的算法，但是第一个函数以直接的方式执行，第二个函数更聪明一点，并且跳过了一部分不必要的工作。

check1是这样的：

// loop length(words1) times
for each word in words1:
    freq1[word]++

// loop length(words2) times
for each word in words2:
    freq2[word]++

// loop length(union(words1, words2)) times
for each word in union(words1, words2):
    score += freq1[word] * freq2[word]

但请记住：当你将某些东西乘以零时，你就会得到零。

这意味着，计算不在两组中的单词的频率是浪费时间 - 我们将频率乘以零，这将不会给分数增加任何内容。

check2将此考虑在内：

// loop length(words1) times
for each word in words1:
    freq1[word]++

// loop length(words2) times
for each word in words2:
    if freq1[word] > 0:
        freq2[word]++

// loop length(intersection(words1, words2)) times
for each word in freq2:
    score += freq1[word] * freq2[word]

包字模型：2个PHP函数，结果相同：为什么？

2 个答案: