$a = array(
        array(
        'id' => 5698,
        'first_name' => 'Peter',
        'last_name' => 'Griffin',
        ),
        array(
        'id' => 4767,
        'first_name' => 'Ben',
        'last_name' => 'Smith',
        ),
        array(
        'id' => 3809,
        'first_name' => 'Joe',
        'last_name' => 'Doe',
        )
    );

print_r($a);
//search first name of the user "Ben"
$firstnameArray = array_column($a,"first_name");
$value = array_search("Ben",$firstnameArray);
print_r($a[$value]);
die;