<?php
$a = array(
"who" => "you", 
"what" => "thing", 
"where" => "place",
"when" => "hour"
);
// the haystack array

$b = array(
"when" => "time", 
"where" => "place", 
"who" => "you",
"what" => "thing"
);

$c = count(array_intersect($a, $b));
echo $c;
?>

3