two level nested aggregation in elastic search based on condition over first level aggregation

My ES document structure is like this:

{
"_index": "my_index",
"_type": "_doc",
"_id": "1296",
"_version": 1,
"_seq_no": 431,
"_primary_term": 1,
"_routing": "1296",
"found": true,
"_source": {
	"id": 1296,
	"test_name": "abc"
	"test_id": 513
	"inventory_arr"[
		{
			"city": "bangalore",
			"after_tat": 168,
			"before_tat": 54,
			"popularity_score": 15,
			"rank": 0,
			"discounted_price": 710,
			"labs": [
				{
					"lab_id": 395,
					"lab_name": "Prednalytics Laboratory",
					"lab_rating": 34,
				},
				{
					"lab_id": 363,
					"lab_name": "Neuberg Diagnostics",
					"lab_rating": 408,
				}
			]
		},
		{
			"city": "mumbai",
			"after_tat": 168,
			"before_tat": 54,
			"popularity_score": 15,
			"rank": 0,
			"discounted_price": 710,
			"labs": [
				{
					"lab_id": 395,
					"lab_name": "Prednalytics Laboratory",
					"lab_rating": 34,
				},
				{
					"lab_id": 380,
					"lab_name": "Neuberg Diagnostics",
					"lab_rating": 408,
				}
			]
		}
	]
}

}

I want to know how many tests are performed in each lab that is in Bangalore.
The problem I'm facing that:
If grouping by lab_id using nested aggregation than it group by each lab no matter in which city it is.

Suppose there is only one record in my doc then I'm expecting answer like this for city Bangalore

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-html -->

[
{key: 395, doc_count: 1}
{key: 363, doc_count: 1}
]

<!-- end snippet -->

Note: lab id can be duplicated in each city.

This problem can be solved using a filter aggregation.

When you are using a nested aggregation, you are iterating over the nested documents. The filter aggregation, filters out the nested documents that don't match the filter query that you provide inside. In your case you would want to filter out the nested documents that aren't inside the city of Bangalore. After you have removed those nested documents you can use another terms bucket aggregation on the lab_id.

Good luck!