140 lines
4.0 KiB
Plaintext
140 lines
4.0 KiB
Plaintext
[[search-aggregations-metrics-valuecount-aggregation]]
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=== Value Count Aggregation
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A `single-value` metrics aggregation that counts the number of values that are extracted from the aggregated documents.
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These values can be extracted either from specific fields in the documents, or be generated by a provided script. Typically,
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this aggregator will be used in conjunction with other single-value aggregations. For example, when computing the `avg`
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one might be interested in the number of values the average is computed over.
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`value_count` does not de-duplicate values, so even if a field has duplicates (or a script generates multiple
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identical values for a single document), each value will be counted individually.
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[source,console]
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--------------------------------------------------
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POST /sales/_search?size=0
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{
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"aggs" : {
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"types_count" : { "value_count" : { "field" : "type" } }
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}
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}
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--------------------------------------------------
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// TEST[setup:sales]
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Response:
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[source,console-result]
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--------------------------------------------------
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{
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...
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"aggregations": {
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"types_count": {
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"value": 7
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}
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}
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}
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--------------------------------------------------
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// TESTRESPONSE[s/\.\.\./"took": $body.took,"timed_out": false,"_shards": $body._shards,"hits": $body.hits,/]
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The name of the aggregation (`types_count` above) also serves as the key by which the aggregation result can be
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retrieved from the returned response.
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==== Script
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Counting the values generated by a script:
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[source,console]
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--------------------------------------------------
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POST /sales/_search?size=0
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{
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"aggs": {
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"type_count": {
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"value_count": {
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"script": {
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"source": "doc['type'].value"
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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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// TEST[setup:sales]
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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:
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[source,console]
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--------------------------------------------------
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POST /sales/_search?size=0
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{
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"aggs": {
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"types_count": {
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"value_count": {
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"script": {
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"id": "my_script",
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"params": {
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"field": "type"
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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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// TEST[setup:sales,stored_example_script]
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NOTE:: Because `value_count` is designed to work with any field it internally treats all values as simple bytes.
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Due to this implementation, if `_value` script variable is used to fetch a value instead of accessing the field
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directly (e.g. a "value script"), the field value will be returned as a string instead of it's native format.
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[[search-aggregations-metrics-valuecount-aggregation-histogram-fields]]
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==== Histogram fields
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When the `value_count` aggregation is computed on <<histogram,histogram fields>>, the result of the aggregation is the sum of all numbers
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in the `counts` array of the histogram.
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For example, for the following index that stores pre-aggregated histograms with latency metrics for different networks:
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[source,console]
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--------------------------------------------------
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PUT metrics_index/_doc/1
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{
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"network.name" : "net-1",
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"latency_histo" : {
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"values" : [0.1, 0.2, 0.3, 0.4, 0.5],
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"counts" : [3, 7, 23, 12, 6] <1>
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}
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}
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PUT metrics_index/_doc/2
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{
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"network.name" : "net-2",
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"latency_histo" : {
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"values" : [0.1, 0.2, 0.3, 0.4, 0.5],
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"counts" : [8, 17, 8, 7, 6] <1>
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}
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}
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POST /metrics_index/_search?size=0
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{
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"aggs": {
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"total_requests": {
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"value_count": { "field": "latency_histo" }
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}
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}
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}
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--------------------------------------------------
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For each histogram field the `value_count` aggregation will sum all numbers in the `counts` array <1>.
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Eventually, it will add all values for all histograms and return the following result:
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[source,console-result]
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--------------------------------------------------
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{
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...
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"aggregations": {
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"total_requests": {
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"value": 97
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}
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}
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}
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--------------------------------------------------
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// TESTRESPONSE[skip:test not setup]
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