OpenSearch/docs/painless/painless-contexts/painless-bucket-selector-ag...

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[[painless-bucket-selector-agg-context]]
=== Bucket selector aggregation context
Use a Painless script in an
{ref}/search-aggregations-pipeline-bucket-selector-aggregation.html[`bucket_selector` aggregation]
to determine if a bucket should be retained or filtered out.
==== Variables
`params` (`Map`, read-only)::
User-defined parameters passed in as part of the query. The parameters
include values defined as part of the `buckets_path`.
==== Return
boolean::
True if the the bucket should be retained, false if the bucket should be filtered out.
==== API
To run this example, first follow the steps in <<painless-context-examples, context examples>>.
The painless context in a `bucket_selector` aggregation provides a `params` map. This map contains both
user-specified custom values, as well as the values from other aggregations specified in the `buckets_path`
property.
Unlike some other aggregation contexts, the `bucket_selector` context must return a boolean `true` or `false`.
This example finds the max of each bucket, adds a user-specified base_cost, and retains all of the
buckets that are greater than `10`.
[source,Painless]
--------------------------------------------------
params.max + params.base_cost > 10
--------------------------------------------------
Note that the values are extracted from the `params` map. The script is in the form of an expression
that returns `true` or `false`. In context, the aggregation looks like this:
[source,js]
--------------------------------------------------
GET /seats/_search
{
"size": 0,
"aggs": {
"theatres": {
"terms": {
"field": "theatre",
"size": 10
},
"aggs": {
"max_cost": {
"max": {
"field": "cost"
}
},
"filtering_agg": {
"bucket_selector": {
"buckets_path": { <1>
"max": "max_cost"
},
"script": {
"params": {
"base_cost": 5 <2>
},
"source": "params.max + params.base_cost > 10"
}
}
}
}
}
}
}
--------------------------------------------------
// CONSOLE
// TEST[setup:seats]
<1> The `buckets_path` points to the max aggregations (`max_cost`) and adds `max` variables
to the `params` map
<2> The user-specified `base_cost` is also added to the `params` map