Accounting for items with multiple Categories and subcategories

exampleScript.txt

DELETE sandbox
PUT sandbox
{
   "mappings": {
      "test-cat": {
         "properties": {
            "title": {
               "type": "string"
            },
            "classifications": {
               "type": "nested",
               "properties": {
                  "category": {
                     "type": "string"
                  },
                  "subcategory": {
                     "type": "string"
                  }
               }
            }
         }
      }
   }
}

DELETE /sandbox/test-cat/1
POST /sandbox/test-cat/1
{
   "title": "Item 1",
   "classifications": [
      {
         "category": "A",
         "subcategory": [
            "A1",
            "A2"
         ]
      },
      {
         "category": "B",
         "subcategory": [
            "B1"
         ]
      }
   ]
}

DELETE /sandbox/test-cat/2
POST /sandbox/test-cat/2
{
   "title": "Item 2",
   "classifications": [
      {
         "category": "A",
         "subcategory": [
            "A1"
         ]
      }
   ]
}

POST /sandbox/test-cat/_search?search_type=count
{
   "aggs": {
      "classifications": {
         "nested": {
            "path": "classifications"
         },
         "aggs": {
            "categories": {
               "terms": {
                  "field": "classifications.category"
               },
               "aggs": {
                  "sub_categories": {
                     "terms": {
                        "field": "classifications.subcategory"
                     }
                  }
               }
            }
         }
      }
   },
   "query": {
      "filtered": {
         "query": {
            "match_all": {}
         }
      }
   }
}