Is it possible to select index values ?

Is it possible to select index values ?

I haven't found any documentation that says "No", but I haven't found anything that says "Yes" either.

The reason - I have a few function indexes that are working as partial indexes.  I'd like to run some analytics on them (to determine uniqueness of values, decide if i should change the function, etc).  It would be easier if I could somehow access the index contents than re-create the index data into a temporary table.