Hi Surya, First, DOW was one of the great contributions by Ian Whitlock and Paul Dorfman. Please refer to this paper for details: http://support.sas.com/resources/papers/proceedings09/038-2009.pdf Second, you can find look ahead details here: http://www.sascommunity.org/wiki/Look-Ahead_and_Look-Back Third, the minor one, 'notsorted' option I used was just trying to use whatever the order in your data as is without sorting it again myself. in other words, I was a little lazy. Please search it in SAS online doc for details. Good Luck, Haikuo
... View more