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Max Aggregation

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Max Aggregation

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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.

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

POST /sales/_search?size=0
{
    "aggs" : {
        "max_price" : { "max" : { "field" : "price" } }
    }
}

Response:

{
    ...
    "aggregations": {
        "max_price": {
            "value": 200.0
        }
    }
}

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

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

POST /sales/_search
{
    "aggs" : {
        "max_price" : {
            "max" : {
                "script" : {
                    "source" : "doc.price.value"
                }
            }
        }
    }
}

This will use the Painless scripting language and no script parameters. To use a stored script use the following syntax:

POST /sales/_search
{
    "aggs" : {
        "max_price" : {
            "max" : {
                "script" : {
                    "id": "my_script",
                    "params": {
                        "field": "price"
                    }
                }
            }
        }
    }
}

Value Script

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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:

POST /sales/_search
{
    "aggs" : {
        "max_price_in_euros" : {
            "max" : {
                "field" : "price",
                "script" : {
                    "source" : "_value * params.conversion_rate",
                    "params" : {
                        "conversion_rate" : 1.2
                    }
                }
            }
        }
    }
}

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.

POST /sales/_search
{
    "aggs" : {
        "grade_max" : {
            "max" : {
                "field" : "grade",
                "missing": 10 
            }
        }
    }
}

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

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