Hi Steve, thanks for your response.

This is totally a work problem, the example I provided is a very simplified version of our actual data. To give you the background: I work for a very large transit agency. In our data, our bus stops are numbered sequentially 1 to n (column 'a'). Every ten or so bus stops, we have a TimePoint, the Timepoint field is null everywhere else (column 'b'). One of our managers wants to know, from one timepoint to another, what is the maximum passenger load, and what the preceding timepoint was. In the current state of our data, I can only find the passenger load AT THE STOP that is a timepoint.

So, if I was able to fill in the nulls with what timepoint those sequence numbers actually belong to, I can then group by that field and take the max(passengerload). I couldn't think of another way of doing this.

Thanks again!