How to do order in grouping(aggregation) in Couchbase?

Question

I have SQL query like this:

select count(id) as ct, city from table group by city order by ct desc

How can I perform this query in Couchbase? I have map function like This:

function (doc, meta) {
  if(doc.city!==null) {
  emit(doc.city,1)
    }
}

and reduce:

_count

my query url is like this: _view/q7?group_level=1&descending=true but it it sort only for key not for value.