elastic facets.json

// mapping
{
  "credits": {
    "properties": {
      "position": {
        "type": "integer"
      },
      "person": {
        "properties": {
        "id": {
          "type": "integer"
        }
      }
    }
  }
}

// query
{
  "size": 0,
  "facets": {
    "top_roles": {
      "terms": {
        "field": "credits.person.id"
      }
    }
  }
}

// Solution using "nested"
{
  "query": {
    "term": {
      "tv": "7"
    }
  },
  "size": 0,
  "facets": {
    "top_cast": {
      "terms_stats": {
        "key_field": "credits.person.id",
        "value_field": "credits.person.position",
        "order": "min"
      },
      "nested": "credits",
      "facet_filter": {
        "term": {
          "credits.department": "actor"
        }
      }
    }
  }
}

// If count is identical for several credits items, 
// is it possible to somehow adjust count and 
// involve second parameter - position, that changes count