Simply convert the date into a time stamp. or just compare the strings. say replace
[EDIT]
You might want to sort the array to get it in the same order the time stamp is probably best for this.
[/EDIT]
$num1=array(1,1,1,2,2,3,4,4,4,5);
with
$num1=array("1st Jan","1st Jan","1st Jan","2nd Jan","2nd Jan","3rd Jan","4th Jan","4th Jan","4th Jan","5th Jan");
Should still work the same.
Mark