A unique pairs version of UNNEST() ?

Hey all, happy new year.

I am trying to get unique pairs from an array of N numbered items, usually
5, but possibly 4 or 6.

If I just wanted unique values, I could do SELECT UNNEST(list_of_ids) AS
id, COUNT(*) FROM table GROUP BY id but in this situation I want all unique
pairs and a COUNT.

For those familiar with python, this is the functionality found in
itertools.combinations. I'm leaning towards just doing this in python, but
I really like keeping as much in SQL as possible.

So in an example where list_of_ids is {1,2,3,4,5} I would essentially get:

{1, 2}
{1, 3}
{1, 4}
{1, 5}
{2, 3}
{2, 4}
{2, 5}
{3, 4}
{3, 5}
{4, 5}

Any tips? Thanks!

--
Wells Oliver
wells(dot)oliver(at)gmail(dot)com <wellsoliver(at)gmail(dot)com>