You should be looking at Facet pivots feature what Solr provides based on
doc-values.
As you are using core Lucene you may have to do little more search on how
to do at low level with Lucene Facet API based on DocValues facet.
Your starting point should be
For an application that already has a Lucene Index, I would like to
implement a facet search that return result aggregations in two
dimensions. From the Lucene examples [1] I can see how to do a simple
facet search that collects facets in one dimension but I haven't seen
any examples for a
