Fetch distinct list of attribute values

In some scenarios, it could be helpful to get a list of distinct attribute values; for example, on a Products dimension with a "color" attribute, return a list of the colors, but each distinct color should appear only once in the result.

One possible implementation might be a new subset option, "Show duplicate attributes", default being true (compatible with current subset results); if false. the Subset would only return the first of elements with distinct attribute values (the first product with color "red", then the first product with attribute "blue" etc.), for the Attirbute selected as "Alias" in the subset. This would also allow showqing a list of distinct attrbute values simply for example in a combobox (by using the "Show Alias" option).