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32e23b9100
Most aggregations (terms, histogram, stats, percentiles, geohash-grid) now support a new `missing` option which defines the value to consider when a field does not have a value. This can be handy if you eg. want a terms aggregation to handle the same way documents that have "N/A" or no value for a `tag` field. This works in a very similar way to the `missing` option on the `sort` element. One known issue is that this option sometimes cannot make the right decision in the unmapped case: it needs to replace all values with the `missing` value but might not know what kind of values source should be produced (numerics, strings, geo points?). For this reason, we might want to add an `unmapped_type` option in the future like we did for sorting. Related to #5324
98 lines
2.8 KiB
Plaintext
98 lines
2.8 KiB
Plaintext
[[search-aggregations-metrics-avg-aggregation]]
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=== Avg Aggregation
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A `single-value` metrics aggregation that computes the average of numeric values that are 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.
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Assuming the data consists of documents representing exams grades (between 0 and 100) of students
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[source,js]
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--------------------------------------------------
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{
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"aggs" : {
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"avg_grade" : { "avg" : { "field" : "grade" } }
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}
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}
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--------------------------------------------------
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The above aggregation computes the average grade over all documents. The aggregation type is `avg` and the `field` setting defines the numeric field of the documents the average will be computed on. The above will return the following:
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[source,js]
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--------------------------------------------------
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{
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...
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"aggregations": {
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"avg_grade": {
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"value": 75
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}
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}
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}
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--------------------------------------------------
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The name of the aggregation (`avg_grade` above) also serves as the key by which the aggregation result can be retrieved from the returned response.
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==== Script
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Computing the average grade based on a script:
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[source,js]
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--------------------------------------------------
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{
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...,
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"aggs" : {
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"avg_grade" : { "avg" : { "script" : "doc['grade'].value" } }
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}
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}
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--------------------------------------------------
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TIP: The `script` parameter expects an inline script. Use `script_id` for indexed scripts and `script_file` for scripts in the `config/scripts/` directory.
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===== Value Script
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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 average:
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[source,js]
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--------------------------------------------------
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{
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"aggs" : {
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...
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"aggs" : {
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"avg_corrected_grade" : {
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"avg" : {
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"field" : "grade",
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"script" : "_value * correction",
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"params" : {
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"correction" : 1.2
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}
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}
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}
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}
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}
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}
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--------------------------------------------------
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==== Missing value
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The `missing` parameter defines how documents that are missing a value should be treated.
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By default they will be ignored but it is also possible to treat them as if they
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had a value.
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[source,js]
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--------------------------------------------------
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{
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"aggs" : {
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"grade_avg" : {
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"avg" : {
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"field" : "grade",
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"missing": 10 <1>
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}
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}
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}
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}
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--------------------------------------------------
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<1> 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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