This would be best accomplished using a parameter. List the three options, and possibly an "All", as parameter values and then created a calculated field with a Case Statement that looks at the chosen parameter value.
Hi Tim, thanks for your help.
I worked it out another way, I classified the Document by Number and lookup for the average it gives me by document.
ZPG2 = 1
If the average = 1.5 it means that both invoice type were against one document, so I did a calculated field that looks up for the the document with an average of 1.5 and If AVG = 1.5 THEN I select the document I needed.