I have a data table that has a datetime column modelled as numeric-continuous. I have various Serial Numbers ("SN", Categorical-Nominal) in another column, along with another Categorical-Nominal column, we can call "Y". I want to see when certain "Y" events occur, so I put the Categorical Nominal Variable on the Y-axis and datetime on the X-axis. For the purposes of this analysis, I choose to split each SN by Page. When I do this, all Pages show all levels of "Y" on the Y-axis. I only want to show the levels applicable to each SN on each Page. Is there a way to exclude levels on specific Pages that don't exist for that group?