[[search-aggregations-metrics-max-aggregation]]
=== Max Aggregation

A `single-value` metrics aggregation that keeps track and returns the maximum
value among the 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.

NOTE: The `min` and `max` aggregation operate on the `double` representation of
the data. As a consequence, the result may be approximate when running on longs
whose absolute value is greater than +2^53+.

Computing the max price value across all documents

[source,console]
--------------------------------------------------
POST /sales/_search?size=0
{
  "aggs": {
    "max_price": { "max": { "field": "price" } }
  }
}
--------------------------------------------------
// TEST[setup:sales]

Response:

[source,console-result]
--------------------------------------------------
{
  ...
  "aggregations": {
      "max_price": {
          "value": 200.0
      }
  }
}
--------------------------------------------------
// TESTRESPONSE[s/\.\.\./"took": $body.took,"timed_out": false,"_shards": $body._shards,"hits": $body.hits,/]

As can be seen, the name of the aggregation (`max_price` above) also serves as
the key by which the aggregation result can be retrieved from the returned
response.

==== Script

The `max` aggregation can also calculate the maximum of a script. The example
below computes the maximum price:

[source,console]
--------------------------------------------------
POST /sales/_search
{
  "aggs" : {
      "max_price" : {
          "max" : {
              "script" : {
                  "source" : "doc.price.value"
              }
          }
      }
  }
}
--------------------------------------------------
// TEST[setup:sales]

This will use the <<modules-scripting-painless, Painless>> scripting language
and no script parameters. To use a stored script use the following syntax:

[source,console]
--------------------------------------------------
POST /sales/_search
{
  "aggs" : {
      "max_price" : {
          "max" : {
              "script" : {
                  "id": "my_script",
                  "params": {
                      "field": "price"
                  }
              }
          }
      }
  }
}
--------------------------------------------------
// TEST[setup:sales,stored_example_script]

==== Value Script

Let's say that the prices of the documents in our index are in USD, but we
would like to compute the max in EURO (and for the sake of this example, let's
say the conversion rate is 1.2). We can use a value script to apply the
conversion rate to every value before it is aggregated:

[source,console]
--------------------------------------------------
POST /sales/_search
{
  "aggs" : {
      "max_price_in_euros" : {
          "max" : {
              "field" : "price",
              "script" : {
                  "source" : "_value * params.conversion_rate",
                  "params" : {
                      "conversion_rate" : 1.2
                  }
              }
          }
      }
  }
}
--------------------------------------------------
// TEST[setup:sales]

==== 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]
--------------------------------------------------
POST /sales/_search
{
  "aggs" : {
      "grade_max" : {
          "max" : {
              "field" : "grade",
              "missing": 10       <1>
          }
      }
  }
}
--------------------------------------------------
// TEST[setup:sales]

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

[[search-aggregations-metrics-max-aggregation-histogram-fields]]
==== Histogram fields

When `max` is computed on <<histogram,histogram fields>>, the result of the aggregation is the maximum
of all elements in the `values` array. Note, that the `counts` array of the histogram is ignored.

For example, for the following index that stores pre-aggregated histograms with latency metrics for different networks:

[source,console]
--------------------------------------------------
PUT metrics_index/_doc/1
{
  "network.name" : "net-1",
  "latency_histo" : {
      "values" : [0.1, 0.2, 0.3, 0.4, 0.5], <1>
      "counts" : [3, 7, 23, 12, 6] <2>
   }
}

PUT metrics_index/_doc/2
{
  "network.name" : "net-2",
  "latency_histo" : {
      "values" :  [0.1, 0.2, 0.3, 0.4, 0.5], <1>
      "counts" : [8, 17, 8, 7, 6] <2>
   }
}

POST /metrics_index/_search?size=0
{
  "aggs" : {
    "min_latency" : { "min" : { "field" : "latency_histo" } }
  }
}
--------------------------------------------------

The `max` aggregation will return the maximum value of all histogram fields:

[source,console-result]
--------------------------------------------------
{
  ...
  "aggregations": {
    "min_latency": {
      "value": 0.5
    }
  }
}
--------------------------------------------------
// TESTRESPONSE[skip:test not setup]
