Php echo user's info only when elements are in common from sql

Question

I'm trying to make all elements from the classlist to display only when they are in common with me and person b. for example if I have classes in position 1,2,5, and I'm on person b's profile who is in class 9,1,8,17,3, It would display ONLY 1 since they both have 1 in their classlist

_{(source: goawaymom.com)}

I've tried a few things like exploding the classlist and giving everything their own variable... Nothing seems to work and I am over complicating everything i try. Does anyone know any simple ways to do this?

<?php
if ($_SESSION['classlist'] == $user_info['classlist']) {
echo ($user_info['classlist']);

} else {
    echo 'No Common Classes';
}
?>

The above code only displays the classlist when the order of the classlist of person a and b have the same classes in the same order.

Answer 1

array_intersect

For example:

// fetch your results from the database
$myclasses = explode(',', $myrow['classlist']);
$theirclasses = explode(',', $theirrow['classlist']);

$common_classes = array_intersect($myclasses, $theirclasses);

Or in your case: (assuming that both $_SESSION['classlist'] and $user_info['classlist'] are strings containing comma separated numbers: '1,2,3,4,5')

$myclasses = explode(',', $_SESSION['classlist']);
$theirclasses = explode(',', $user_info['classlist']);
$common_classes = array_intersect($myclasses, $theirclasses);

if (count($common_classes) > 0)
{
    echo '<p>You have the following classes in common.</p>';
    echo '<ul>';
    foreach ($common_classes as $class)
    {
        echo '<li>' . $class . '</li>';
    }
    echo '</ul>';
}
else
{
    echo '<p>Billy no mates :(</p>';
}