Count of the result of a MongoDB aggregate query

After I write a MongoDB aggregate command, I would like to quickly look at the number of results it returned.

Say, my query is something like this: (probably more complex)

db.zipcodes.aggregate( [{ $group :
                            { _id : "$state" } }])

Then, right now I do the following to get a total count:

 db.zipcodes.aggregate( [{ $group :
                            { _id : "$state" }},
                         {'$group': {_id: null, count: {$sum: 1}}}])

Is there another quicker way to get a count of the results of a MongoDB aggregate query?

PS: I've just seen a related question: MongoDB Aggregation: How to get total records count? . Has there been any progress regarding this?

Copyright Notice：Content Author:「Phani」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/24417175/count-of-the-result-of-a-mongodb-aggregate-query