It would be useful to be able to add a documents position in a sort to the document. For example, there could be an additional option to the $sort stage:

{$sort: {
    order: {a: 1, b: 1},
    includeSortIndex: 'index'
}}

Which would output documents sorted by {a: 1, b: 1}, and inject an additional field 'index', containing it's position in the sort order (overwriting an existing field if applicable).

Original Description

Originally posted

https://groups.google.com/d/topic/mongodb-user/PL_g1RCmPsI/discussion

It would be very useful to be able to extract the indexed position of a document from a group statement, or a sort. e.g. consider the use case of building up a leader board / league table.

Workaround suggestions welcome in the meantime.