Php 确定数组中的哪个字在字符串中

我有一个字符串：

$str = "Hello is a greeting";

我有一系列的词：

$equals = array("is", "are", "was", "were", "will", "has", "have", "do", "does");

我正在尝试查看字符串中的单词：

$words = explode(" ", $str);
$new_association = false;
foreach($words as $word) {
    if(in_array($word, $equals)) {
        $new_association = true;
        $e['response'] = 'You made an association.';
        // determine which 'equals' word was used.      
        // $equal_used = 'is';
    }
}

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如何确定使用了哪一个相等词？

上面马克的回答是比较好的，但如果你想坚持目前的方法：

$new_asscociation = false;
$equal_used = array_intersect($equals, explode(' ', $str)); 
if (!empty($equal_used)) { 
    $new_asscociation = true; 
    var_dump($equal_used); 
}

$words = explode(" ", $str);
$new_association = false;
foreach($words as $word) {
    if(in_array($word, $equals)) {
        $new_association = true;
        $e['response'] = 'You made an association.';
        // determine which 'equals' word was used.      
        $equal_used = $word;
    }
}

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如果我只想要以字符串形式出现的值怎么办？如果有多个值，您希望哪一个作为字符串。但是您可以执行

$equal\u used=内爆（“”，$equal\u used）以创建字符串