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Elastic Docs ›Elasticsearch Guide [8.8] ›Aggregations ›Metrics aggregations

Stats aggregation

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Stats aggregation

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A multi-value metrics aggregation that computes stats over numeric values extracted from the aggregated documents.

The stats that are returned consist of: min, max, sum, count and avg.

Assuming the data consists of documents representing exams grades (between 0 and 100) of students

response = client.search(
  index: 'exams',
  size: 0,
  body: {
    aggregations: {
      grades_stats: {
        stats: {
          field: 'grade'
        }
      }
    }
  }
)
puts response
POST /exams/_search?size=0
{
  "aggs": {
    "grades_stats": { "stats": { "field": "grade" } }
  }
}

The above aggregation computes the grades statistics over all documents. The aggregation type is stats and the field setting defines the numeric field of the documents the stats will be computed on. The above will return the following:

{
  ...

  "aggregations": {
    "grades_stats": {
      "count": 2,
      "min": 50.0,
      "max": 100.0,
      "avg": 75.0,
      "sum": 150.0
    }
  }
}

The name of the aggregation (grades_stats above) also serves as the key by which the aggregation result can be retrieved from the returned response.

Script

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If you need to get the stats for something more complex than a single field, run the aggregation on a runtime field.

response = client.search(
  index: 'exams',
  body: {
    size: 0,
    runtime_mappings: {
      "grade.weighted": {
        type: 'double',
        script: "\n        emit(doc['grade'].value * doc['weight'].value)\n      "
      }
    },
    aggregations: {
      grades_stats: {
        stats: {
          field: 'grade.weighted'
        }
      }
    }
  }
)
puts response
POST /exams/_search
{
  "size": 0,
  "runtime_mappings": {
    "grade.weighted": {
      "type": "double",
      "script": """
        emit(doc['grade'].value * doc['weight'].value)
      """
    }
  },
  "aggs": {
    "grades_stats": {
      "stats": {
        "field": "grade.weighted"
      }
    }
  }
}

Missing value

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The missing parameter defines how documents that are missing a value should be treated. By default they will be ignored but it is also possible to treat them as if they had a value.

response = client.search(
  index: 'exams',
  size: 0,
  body: {
    aggregations: {
      grades_stats: {
        stats: {
          field: 'grade',
          missing: 0
        }
      }
    }
  }
)
puts response
POST /exams/_search?size=0
{
  "aggs": {
    "grades_stats": {
      "stats": {
        "field": "grade",
        "missing": 0      
      }
    }
  }
}

Documents without a value in the grade field will fall into the same bucket as documents that have the value 0.
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