Returns an aggregation of the first n elements within a group. The elements returned are meaningful only if in a specified sort order. If the group contains fewer than n elements, $firstN returns all elements in the group.
The input array
The right-hand side expression value of the operator
The options to use for this operation
Returns an aggregation of the first n elements within a group. The elements returned are meaningful only if in a specified sort order. If the group contains fewer than n elements, $firstN returns all elements in the group.