Proposal: array_unique_agg() function

Hi hackers,

I needed an aggregate function similar to array_agg() but which
aggregates only unique values. As it turned out there is no convenient
way of doing this. What I ended up doing instead was aggregating to
JSONB keys and then converting a JSONB object to an array:

SELECT array(select jsonb_object_keys(jsonb_object_agg(mycolumn, true)))
FROM ...

This works but doesn't seem to be the greatest user experience. I
would like to submit a patch that adds array_unique_agg() function
unless anyone has strong objections to this feature.

-- 
Best regards,
Aleksander Alekseev