Complete a MongoDB query to group and sum fields - mongodb

Question

I'm doing an app which simulates a hotel check in, where the user registers a lot of client's data. Among this data, I have this:
{
"client_name" : "John Doe",
"client_id" : "xxxxxxxx"
...
"company" : "CocaCola",
"hotel_hq" : "New York",
"lodging_days" : 5,
...
}
One of the functions that should have the app is to show the list of hotel headquarters that the company attends, and the number of days that the company use in every HQ.
So, I need a query that returns me something like this:
{"company" : "CocaCola", "hotel_hq" : ["New York", "California", "Orlando"], "lodging_days" : [5, 10, 8]}
I make, with blood sweat and tears, this query:
db.clients.aggregate(
{
$group: {
_id: '$company',
hotel_hq : {$push:'$hotel_hq'},
lodging_days : {$push:'$lodging_days' }
}
})
And it's the closest I've been, because that returns me this:
{"_id" : "CocaCola", "hotel_hq": ["New York", "New York", "California", "Orlando", "Orlando", "Orlando", "Orlando"], "lodging_days" : [5, 8, 10, 8, 9, 2, 3]}
The hotel HQ are sometimes repeated because differents clients of the same company stayed in the same HQ, or the same client does it more than one time.
Obviously, I can change $push to $addToSet, but the result going to be:
{"_id" : "CocaCola", "hotel_hq": ["New York", "California", "Orlando"], "lodging_days" : [5, 8, 10, 9, 2, 3]}
Which is cool for the hotel_hq, but no for the lodging_days, I try with a $sum, but I don't know how to say Mongo to sum only the 'lodging_days' of a repeated 'hotel_hq'.

Answer 1

hope this works..
db.test3.aggregate(
[
{
$group:{_id:{company:"$company",hotel_hq:"$hotel_hq"},
"Days":{$sum:"$lodging_days"}}
},
{
$group:{_id:"$company",hotel_hq:{$push:"$_id.hotel_hq"},
Days:{$push:"$Days"}}
}
]
)