Does Tamino support "distinct-values" function?

Does Tamino support “distinct-values” function? As I know, I don’t support it yet. Well I want to know if there is any plan to support it. Without it, I can not group xml data on Tamino.

the function distinct-values is currently not available in Tamino XQuery 4.
It is high on the priority list for the next version.
Under certain circumstances a workaround may be used with a self join like this:

declare namespace tf = “

for $b in input()/bib/book
where tf:getInoId(root($b)) eq
for $c in input()/bib/book
where $b/@year eq $c/@year
return tf:getInoId(root($c))
return $b

But be aware that such a complex construction is currently not optimized at all.

Best regards