1. I might not understand your data correctly, why not create a filter on Server that excludes Null values?
2. Given that you have 4 ranks, you could create a calculated field that would use the parameter value. I created one in the attached workbook using:
IF INDEX() <= [Parameter 1] THEN INDEX() END
Put the calculated field on the Filter shelf and start dragging the slider around.
filter ranks using slider.twbx.zip 165.7 KB