WARNING: Version 1.4 of Elasticsearch has passed its EOL date.

This documentation is no longer being maintained and may be removed. If you are running this version, we strongly advise you to upgrade. For the latest information, see the current release documentation.

« Stats Aggregation Value Count Aggregation »
Elastic Docs ›Elasticsearch Guide [1.4] ›Search APIs ›Aggregations

Extended Stats Aggregation

edit

Extended Stats Aggregation

edit

A multi-value metrics aggregation that computes stats over numeric values extracted from the aggregated documents. These values can be extracted either from specific numeric fields in the documents, or be generated by a provided script.

The extended_stats aggregations is an extended version of the stats aggregation, where additional metrics are added such as sum_of_squares, variance, std_deviation and std_deviation_bounds.

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

{
    "aggs" : {
        "grades_stats" : { "extended_stats" : { "field" : "grade" } }
    }
}

The above aggregation computes the grades statistics over all documents. The aggregation type is extended_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": {
        "grade_stats": {
           "count": 9,
           "min": 72,
           "max": 99,
           "avg": 86,
           "sum": 774,
           "sum_of_squares": 67028,
           "variance": 51.55555555555556,
           "std_deviation": 7.180219742846005,
           "std_deviation_bounds": {
            "upper": 100.36043948569201,
            "lower": 71.63956051430799
           }
        }
    }
}

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.

Standard Deviation Bounds

edit

Added in 1.4.3.

By default, the extended_stats metric will return an object called std_deviation_bounds, which provides an interval of plus/minus two standard deviations from the mean. This can be a useful way to visualize variance of your data. If you want a different boundary, for example three standard deviations, you can set sigma in the request:

{
    "aggs" : {
        "grades_stats" : {
            "extended_stats" : {
                "field" : "grade",
                "sigma" : 3 
            }
        }
    }
}

sigma controls how many standard deviations +/- from the mean should be displayed [1.4.3] Added in 1.4.3.

sigma can be any non-negative double, meaning you can request non-integer values such as 1.5. A value of 0 is valid, but will simply return the average for both upper and lower bounds.

Standard Deviation and Bounds require normality

The standard deviation and its bounds are displayed by default, but they are not always applicable to all data-sets. Your data must be normally distributed for the metrics to make sense. The statistics behind standard deviations assumes normally distributed data, so if your data is skewed heavily left or right, the value returned will be misleading.

Script

edit

Computing the grades stats based on a script:

{
    ...,

    "aggs" : {
        "grades_stats" : { "extended_stats" : { "script" : "doc['grade'].value" } }
    }
}

Value Script

edit

It turned out that the exam was way above the level of the students and a grade correction needs to be applied. We can use value script to get the new stats:

{
    "aggs" : {
        ...

        "aggs" : {
            "grades_stats" : {
                "extended_stats" : {
                    "field" : "grade",
                    "script" : "_value * correction",
                    "params" : {
                        "correction" : 1.2
                    }
                }
            }
        }
    }
}
« Stats Aggregation Value Count Aggregation »