Syntax

{$reverseArray: <expression which evaluates to an array>}

Examples

Input

{_id: 0, a: [1, 2, 3]}

Pipeline

db.coll.aggregate([{
    $project: {
        reversed: {$reverseArray: "$a"}
    }
}])

Output

{_id: 0, reversed: [3, 2, 1]}

Additional Notes

• Can be used in combination with $reduce to yield the equivalent of a $foldR.
• Returns null if input is nullish.
• Errors if input is not an array or nullish.

Original Description

Aggregation should support an $reverseArray expression, which accepts as input an expression that evaluates to an array, and outputs the reversed version of the array. Throws an error if the input is not an array or nullish.