102 lines
2.7 KiB
Plaintext
102 lines
2.7 KiB
Plaintext
[[search-facets-statistical-facet]]
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=== Statistical Facet
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Statistical facet allows to compute statistical data on a numeric
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fields. The statistical data include count, total, sum of squares, mean
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(average), minimum, maximum, variance, and standard deviation. Here is
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an example:
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[source,js]
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--------------------------------------------------
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{
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"query" : {
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"match_all" : {}
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},
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"facets" : {
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"stat1" : {
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"statistical" : {
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"field" : "num1"
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}
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}
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}
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}
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--------------------------------------------------
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==== Script field
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When using `field`, the numeric value of the field is used to compute
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the statistical information. Sometimes, several fields values represent
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the statistics we want to compute, or some sort of mathematical
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evaluation. The script field allows to define a
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<<modules-scripting,script>> to evaluate, with
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its value used to compute the statistical information. For example:
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[source,js]
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--------------------------------------------------
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{
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"query" : {
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"match_all" : {}
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},
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"facets" : {
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"stat1" : {
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"statistical" : {
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"script" : "doc['num1'].value + doc['num2'].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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Parameters can also be provided to the different scripts (preferable if
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the script is the same, with different values for a specific parameter,
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like "factor"):
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[source,js]
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--------------------------------------------------
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{
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"query" : {
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"match_all" : {}
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},
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"facets" : {
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"stat1" : {
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"statistical" : {
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"script" : "(doc['num1'].value + doc['num2'].value) * factor",
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"params" : {
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"factor" : 5
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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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==== Multi Field
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The statistical facet can be executed against more than one field,
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returning the aggregation result across those fields. For example:
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[source,js]
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--------------------------------------------------
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{
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"query" : {
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"match_all" : {}
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},
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"facets" : {
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"stat1" : {
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"statistical" : {
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"fields" : ["num1", "num2"]
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}
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}
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}
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}
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--------------------------------------------------
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==== Memory Considerations
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In order to implement the statistical facet, the relevant field values
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are loaded into memory from the index. This means that per shard, there
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should be enough memory to contain them. Since by default, dynamic
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introduced types are `long` and `double`, one option to reduce the
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memory footprint is to explicitly set the types for the relevant fields
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to either `short`, `integer`, or `float` when possible.
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