MongoDB Documentation, Release 3.0.4 7.5 Additional Resources • MongoDB Analytics: Learn Aggregation by Example: Exploratory Analytics and Visualization Using Flight Data 25 • MongoDB for Time Series Data: Analyzing Time Series Data Using the Aggregation Framework and Hadoop 26 • The Aggregation Framework 27 • Webinar: Exploring the Aggregation Framework 28 • Quick Reference Cards 29 $^{25}$http://www.mongodb.com/presentations/mongodb-analytics-learn-aggregation-example-exploratory-analytics-and-visualization?jmp=docs $^{26}$http://www.mongodb.com/presentations/mongodb-time-series-data-part-2-analyzing-time-series-data-using-aggregation- framework?jmp=docs $^{27}$https://www.mongodb.com/presentations/aggregation-framework-0?jmp=docs $^{28}$https://www.mongodb.com/webinar/exploring-the-aggregation-framework?jmp=docs $^{29}$https://www.mongodb.com/lp/misc/quick-reference-cards?jmp=docs 7.5. Additional Resources 479 $let , $redact , $map Variable Description ROOT References the root document, i.e. the top-level doc- ument, currently being processed in the aggregation pipeline stage. CURRENT References the start of the field path being processed in the aggregation pipeline stage. Unless documented oth- erwise, all stages start with CURRENT (page 479) the same as ROOT (page 479). CURRENT (page 479) is modifiable. However, since $<field> is equivalent to $$CURRENT.<field> , rebinding CURRENT (page 479) changes the meaning of $ accesses. DESCEND One of the allowed results of a $redact expression. PRUNE One of the allowed results of a $redact expression. KEEP One of the allowed results of a $redact expression. See also: