CODEWITHSUNDEEP
mongodbaggregation-framework
Max Paymar
Max Paymar

Reputation: 718

Count unique keys - mongo aggregation pipeline

I have a mongo collection of searches. Each search has a criteria object, which can have any combination of criteria. So something like: 

{
    "_id": 1,
    "criteria": {
        "state": ["NY", "IL"]
        ... 
    },
    ...
}

I'm building a mongo aggregation pipeline, and I'm wondering how to project only the keys so that I can count them.

So far the first step of my pipeline is:

db.userSearch.aggregate([
    { "$project": { "criteria":1 } },
    ...
])

This returns all of the criteria objects correctly, now I need to project the keys somehow. Does anyone have any ideas?

Edit: desired output: {"state":20, "balance":5, "geolocation":10, ...}

Upvotes: 0

Views: 196

Answers (1)

Max Paymar
Max Paymar

Reputation: 718

In case anyone was wondering, I used mapReduce as follows.

map = function() {
    Object.keys(this.criteria).forEach(function(k) {
        emit(k, 1)
    })
}

reduce = function(k, vals) {
    return Array.sum(vals)
}

db.userSearch.mapReduce(map, reduce, 'out')

Upvotes: 1

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