Although I am not completely sure of the desired outcome, I believe creating a calculated field similar to the following will allow the user to filter out different types of files:
if contains([Description], ".dup") then "dup files"
elseif contains([Description], ".gr") then "gr files"
Then, by placing this on the view, the user will be able to see all the same type of files together.
I hope this helps!
In this specific case, perhaps ENDSWITH() would be more accurate, if you could first truncate the part at the end which looks consistent.