How to $ click a field depending on state?

Question

I am trying to conditionally push a field to an array during the $ group stage of the MongoDB aggregation pipeline.

Essentially, I have documents with a username and an array of actions that they performed.

If I group user actions as follows:

{ $group: { _id: { "name": "$user.name" }, "actions": { $push: $action"} } }

I get the following:

[{
    "_id": {
        "name": "Bob"
    },
    "actions": ["add", "wait", "subtract"]
}, {
    "_id": {
        "name": "Susan"
    },
    "actions": ["add"]
}, {
    "_id": {
        "name": "Susan"
    },
    "actions": ["add, subtract"]
}]

So far so good. The idea would now be to group an array of actions to see which set of user actions is most popular. The problem is that I need to remove the "wait" action before taking the group into account. Therefore, the result should be something like this, taking into account that the "wait" element should not be considered in a grouping:

[{
    "_id": ["add"],
    "total": 1
}, {
    "_id": ["add", "subtract"],
    "total": 2
}]

---

Test number 1

If I add this step to $ group:

{ $group : { _id : "$actions", total: { $sum: 1} }}

, , wait.

[{
    "_id": ["add"],
    "total": 1
}, {
    "_id": ["add", "subtract"],
    "total": 1
}, {
    "_id": ["add", "wait", "subtract"],
    "total": 1
}] 

№ 2

{ $group: { _id: { "name": "$user.name" }, "actions": { $push: { $cond: { if: 
{ $ne: [ "$action", 'wait']}, then: "$action", else: null } }}} }


{ $group : { _id : "$actions", total: { $sum: 1} }}

, , , , , .

[{
    "_id": ["add"],
    "total": 1
}, {
    "_id": ["add", "subtract"],
    "total": 1
}, {
    "_id": ["add", null, "subtract"],
    "total": 1
}]

---

UPDATE:

:

{
    "_id": ObjectID("573e0c6155e2a8f9362fb8ff"),
    "user": {
        "name": "Bob",
    },
    "action": "add",
}

Answer 1

$match , , "" "",.

db.collection.aggregate([
    { "$match": { "action": { "$ne": "wait" } } },
    { "$group": { 
        "_id": "$user.name", 
       "actions": { "$push": "$action" }, 
       "total": { "$sum": 1 } 
    }}
])