As we mentioned previously, Spotfire expressions do not work in the same way as Excel formulas. Expressions must work over the whole of the data that's currently in scope (be it the whole data table or a grouping within a visualization).

Spotfire provides a set of OVER functions to allow you to aggregate data over the nodes of a hierarchy in a data table. At its simplest level, the OVER function is a means to define at what granularity you wish to aggregate values.

The nodes of a hierarchy are the unique values in each level of the hierarchy. Perhaps the easiest type of hierarchy to think of is a date. The levels of the date hierarchy could be year/month/day. The nodes at each of the levels are the unique values at each level in that hierarchy. So, given a date column, you could imagine the nodes as the individual boxes that are...