[role="xpack"]
[testenv="basic"]
[[search-aggregations-metrics-boxplot-aggregation]]
=== Boxplot aggregation
++++
<titleabbrev>Boxplot</titleabbrev>
++++

A `boxplot` metrics aggregation that computes boxplot of numeric values extracted from the aggregated documents.
These values can be generated by a provided script or extracted from specific numeric or
<<histogram,histogram fields>> in the documents.

The `boxplot` aggregation returns essential information for making a {wikipedia}/Box_plot[box plot]: minimum, maximum
median, first quartile (25th percentile)  and third quartile (75th percentile) values.

==== Syntax

A `boxplot` aggregation looks like this in isolation:

[source,js]
--------------------------------------------------
{
  "boxplot": {
    "field": "load_time"
  }
}
--------------------------------------------------
// NOTCONSOLE

Let's look at a boxplot representing load time:

[source,console]
--------------------------------------------------
GET latency/_search
{
  "size": 0,
  "aggs": {
    "load_time_boxplot": {
      "boxplot": {
        "field": "load_time" <1>
      }
    }
  }
}
--------------------------------------------------
// TEST[setup:latency]
<1> The field `load_time` must be a numeric field

The response will look like this:

[source,console-result]
--------------------------------------------------
{
  ...

 "aggregations": {
    "load_time_boxplot": {
      "min": 0.0,
      "max": 990.0,
      "q1": 165.0,
      "q2": 445.0,
      "q3": 725.0,
      "lower": 0.0,
      "upper": 990.0
    }
  }
}
--------------------------------------------------
// TESTRESPONSE[s/\.\.\./"took": $body.took,"timed_out": false,"_shards": $body._shards,"hits": $body.hits,/]

In this case, the lower and upper whisker values are equal to the min and max.  In general, these values are the 1.5 *
IQR range, which is to say the nearest values to `q1 - (1.5 * IQR)` and `q3 + (1.5 * IQR)`.  Since this is an approximation, the given values
may not actually be observed values from the data, but should be within a reasonable error bound of them.  While the Boxplot aggregation
doesn't directly return outlier points, you can check if `lower > min` or `upper < max` to see if outliers exist on either side, and then
query for them directly.

==== Script

The boxplot metric supports scripting.  For example, if our load times
are in milliseconds but we want values calculated in seconds, we could use
a script to convert them on-the-fly:

[source,console]
--------------------------------------------------
GET latency/_search
{
  "size": 0,
  "aggs": {
    "load_time_boxplot": {
      "boxplot": {
        "script": {
          "lang": "painless",
          "source": "doc['load_time'].value / params.timeUnit", <1>
          "params": {
            "timeUnit": 1000                                    <2>
          }
        }
      }
    }
  }
}
--------------------------------------------------
// TEST[setup:latency]

<1> The `field` parameter is replaced with a `script` parameter, which uses the
script to generate values which percentiles are calculated on
<2> Scripting supports parameterized input just like any other script

This will interpret the `script` parameter as an `inline` script with the `painless` script language and no script parameters. To use a
stored script use the following syntax:

[source,console]
--------------------------------------------------
GET latency/_search
{
  "size": 0,
  "aggs": {
    "load_time_boxplot": {
      "boxplot": {
        "script": {
          "id": "my_script",
          "params": {
            "field": "load_time"
          }
        }
      }
    }
  }
}
--------------------------------------------------
// TEST[setup:latency,stored_example_script]

[[search-aggregations-metrics-boxplot-aggregation-approximation]]
==== Boxplot values are (usually) approximate

The algorithm used by the `boxplot` metric is called TDigest (introduced by
Ted Dunning in
https://github.com/tdunning/t-digest/blob/master/docs/t-digest-paper/histo.pdf[Computing Accurate Quantiles using T-Digests]).

[WARNING]
====
Boxplot as other percentile aggregations are also
{wikipedia}/Nondeterministic_algorithm[non-deterministic].
This means you can get slightly different results using the same data.
====

[[search-aggregations-metrics-boxplot-aggregation-compression]]
==== Compression

Approximate algorithms must balance memory utilization with estimation accuracy.
This balance can be controlled using a `compression` parameter:

[source,console]
--------------------------------------------------
GET latency/_search
{
  "size": 0,
  "aggs": {
    "load_time_boxplot": {
      "boxplot": {
        "field": "load_time",
        "compression": 200    <1>
      }
    }
  }
}
--------------------------------------------------
// TEST[setup:latency]

<1> Compression controls memory usage and approximation error

include::percentile-aggregation.asciidoc[tags=t-digest]

==== Missing value

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.

[source,console]
--------------------------------------------------
GET latency/_search
{
  "size": 0,
  "aggs": {
    "grade_boxplot": {
      "boxplot": {
        "field": "grade",
        "missing": 10     <1>
      }
    }
  }
}
--------------------------------------------------
// TEST[setup:latency]

<1> Documents without a value in the `grade` field will fall into the same bucket as documents that have the value `10`.
