Rollup Aggregation Stage
The Rollup Aggregation query-pipeline stage (previously called the Rollup Aggregator stage) is used to rollup Solr results from a context variable. If using the REST API, this stage type is named "rollup-rec-aggr".
This stage reads the Solr results (SolrResponse.class) from the context and rolls up over a single field product a list of unique IDs and also aggregates the weights (any numeric filed in Solr) for those IDs using any of the statistical aggregation functions available. The result from aggregation is saved back in the context and can later be used in the Parameterized Boosting stage.
When entering configuration values in the UI, use unescaped characters, such as