MongoDB - Average fields values over documents - mongodb

Question

I have a collection with this schema:
{
"fields":
{
"field1": [
{"name": "abc", "value": 2},
{"name": "bcd", "value": 4},
{"name": "cde", "value": 6}
],
"field2": [
{"name": "dec", "value": 3},
{"name": "das", "value": 8},
{"name": "pam", "value": 10}
]
}
},
{
"fields":
{
"field1": [
{"name": "abc", "value": 7},
{"name": "cde", "value": 12}
],
"field2": [
{"name": "dec", "value": 3},
{"name": "das", "value": 8},
{"name": "pam", "value": 10}
]
}
}
What I'm trying to obtain is e.g. the average values of all members of 'field1', evaluating 0 if a member exist in a document but not in another (like 'bcd').
So in this example I should get:
{
'_id': 'abc',
'avg': 4.5
},
{
'_id': 'bcd',
'avg': 2
},
{
'_id': 'cde',
'avg': 9
}
I wrote this aggregation query but I'm pretty sure there is something wrong with it:
db.statuses.aggregate([
{
$unwind: '$fields.field1'
},
{
$group: {
_id: '$fields.field1.name',
avg: {
$avg: '$fields.field1.value'
}
}
},
{
$sort: {
avg: -1
}
}
])
I think I should add a step before the average calculation in which I have to build an array of all values for each name (0 if the name does not exist in a document), and then evaluate the average on these arrays. Am I right?
How could I do this?