There are two things you need to do to troubleshoot this problem. INSIDE your function, at the very top, do this:

First, echo out one of the arrays like this:
[PHP]
echo "<pre>";
print_r($Date_Added);
echo "</pre>";
[/PHP]

Then echo out the value of $num:
[PHP]
echo "<hr />".$num;
[/PHP]

You should see that $num = 0, but that your array does not even exist. You forgot one important line at the top of your function:
[PHP]
global $Date_Added, $Sample_Views;
[/PHP]