[COMPASS-7582] Investigate changes in PM-3160: Expose the array index in a $map operation Created: 17/Jan/24  Updated: 22/Jan/24

Status: Needs Triage
Project: Compass
Component/s: None
Affects Version/s: None
Fix Version/s: None

Type: Investigation Priority: Major - P3
Reporter: Backlog - Core Eng Program Management Team Assignee: Unassigned
Resolution: Unresolved Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
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Epic Link: COMPASS-7048

 Description   
Original Downstream Change Summary

New options will be added to $map, $filter and $reduce, allowing users to reference the array index of the element to which the operator's expression is currently being applied.

Description of Linked Ticket

Epic Summary

Summary

Extend $map, $filter, $reduce to expose the index of array element.

Motivation

Sometimes when working with arrays the logic depends on the position of the element. E.g. two-dimentional array represents values on the grid, and element index is a coordinate on X/Y axis; or user may want to select every other element of the array to create a sample for A/B test or parallel processing.
It's pretty cumbersome to calculate position of the element today, so we'd like to introduce a simplified syntax for it.
Example from Paul's book

Documentation

Product Description
Scope
Syntax
Technical Design
Docs Update


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