select distinct(cookie) from table;

map2 = Code("function () { emit(this.cookie, 1);}")
reduce2 = Code("function (key, values) {return 1;}")
totalunique = collection.map_reduce(map2, reduce2, out={"reduce":aggregatedcollection}, query=query).count();

var options = {out: { "inline": 1 }, query : query};
db.colls.mapReduce(_mapper, _reducer, options);