根据以前的组计算唯一条目

Trying to find unique values in each group, however with a look back at the previously grouped items. It will be group by time, so if previous time block had the unique value it should not appear in the next time block. Lookback should span all previous time blocks. So at time 2, it looks at time 0 and 1, while at time 10 it looks back at time 0 to 9.Trying to find unique values in each group, how