How to return a string array with mongodb aggregation

Question

I need to return a string array with mongodb aggregation. I have done the following:

db.users.aggregate([{$group: {_id:"$emails.address"}}])

It returns:

{ "_id" : [ "[e-mail]" ] }
{ "_id" : [ "[e-mail]" ] }
{ "_id" : [ "[e-mail]" ] }

Is there a way to return an array of string like this:

["[e-mail]","[e-mail]","[e-mail]"]

Many thanks to everyone who is in no hurry to help me ..

EDIT

Adding data:

{
    "_id" : "ukn9MLo3hRYEpCCty",
    "createdAt" : ISODate("2015-10-24T03:52:11.960Z"),
    "emails" : [
        {
            "address" : "[e-mail]",
            "verified" : false
        }
    ]
}
{
    "_id" : "5SXRXraariyhRQACe",
    "createdAt" : ISODate("2015-10-24T03:52:12.093Z"),
    "emails" : [
        {
            "address" : "[e-mail]",
            "verified" : false
        }
    ]
}
{
    "_id" : "WMHWxeymY4ATWLXjz",
    "createdAt" : ISODate("2015-10-24T03:52:12.237Z"),
    "emails" : [
        {
            "address" : "[e-mail]",
            "verified" : false
        }
    ]
}

Answer 1

The method .aggregate()always returns Objectsno matter what you do and which cannot change.

For your purpose, you are probably better off using .distinct()instead, which returns an array of different values:

db.users.distinct("emails.address");

This is exactly what you need:

["[e-mail]","[e-mail]","[e-mail]"]

.aggregate(), "" -. $unwind .

JavaScript .map(), :

db.users.aggregate([
    { "$unwind": "$emails" },
    { "$group": { "_id": "$emails.address" } }
]).map(function(el) { return el._id })

, .map() , .

Answer 2

.

.aggregate() , .

, .

, , node .

db.users.aggregate([
     { "$unwind": "$emails" },
     { "$group": { "_id": null, emails:{$push:"$emails.address"} } },
     { "$project":{emails:true,_id:false}}
 ])

:

{ "emails" : [ "[e-mail]", "[e-mail]", "[e-mail]" ] }