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Count Aggregation

A single-value metrics aggregation that counts the number of values that are extracted from the aggregated documents.

Typically, this aggregator will be used in conjunction with other single-value aggregations. For example, when computing the _avg one might be interested in the number of values the average is computed over.

Structuring

The following snippet captures the structure of count aggregations:

"<aggregation_name>": {
  "_count": {
    "_field": "<field_name>"
  },
  ...
}

Field

The <field_name> in the _field parameter defines the specific field from which the numeric values in the documents are extracted and used to compute the returned count.

Assuming the data consists of documents representing bank accounts, as shown in the sample dataset of Data Exploration section, computing the number of cities with accounts in the state of Indiana:

SEARCH /bank/
{
  "_query": {
    "contact.state": "Indiana"
  },
  "_limit": 0,
  "_check_at_least": 1000,
  "_aggs": {
    "indiana_city_count": {
      "_count": {
        "_field": "contact.city"
      }
    }
  }
}

Response:

  "aggregations": {
    "_doc_count": 17,
    "indiana_city_count": {
      "_count": 17
    }
  }, ...

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