facets with sum(value) instead of count(*)

[Luke Rosiak]

Is there a version of the list facet that shows the sum of a numeric
attribute in a set of items rather than, or in addition to, the number
of times an item appears?

So if I had a collection:

[{course},{price},
'appetizer',5,
'appetizer,7,
'entree','20',
'entree','30']

The facet would look like:

(50) Entree
(12) Appetizer

instead of

(2) Entree
(2) Appetizer