Number of count instances in all documents with mongo

Question

I am trying to extract data from a collection of documents that look like this:

[
  {
    name: 'john',
    sex: 'male',
    hobbies: ['football', 'tennis', 'swimming']
  },
  {
    name: 'betty'
    sex: 'female',
    hobbies: ['football', 'tennis']
  },
  {
    name: 'frank'
    sex: 'male',
    hobbies: ['football', 'tennis']
  } 
]

I am trying to use an aggregation structure to represent data disaggregated by sex, considering the most common hobbies. The results should look something like this.

{ _id: 'male', 
  total: 2, 
  hobbies: {
    football: 2,
    tennis: 2,
    swimming: 1
  } 
},
{ _id: 'female', 
  total: 1, 
    hobbies: {
      football: 1,
      tennis: 1
    } 
}

So far, I could get the total of each gender, but I'm not sure how I could use to get the totals of a hobby array.

My code is:

collection.aggregate([
        { 
            $group: { 
                _id: '$sex', 
                total: { $sum: 1 }
            }
        }
    ])

Answer 1

"" . , .

, , "" "" , :

db.people.aggregate([
    { "$group": {
        "_id": "$sex",
        "hobbies": { "$push": "$hobbies" },
        "total": { "$sum": 1 }
    }},
    { "$unwind": "$hobbies" },
    { "$unwind": "$hobbies" },
    { "$group": {
        "_id": {
            "sex": "$_id",
            "hobby": "$hobbies"
        },
        "total": { "$first": "$total" },
        "hobbyCount": { "$sum": 1 }
    }},
    { "$group": {
        "_id": "$_id.sex",
        "total": { "$first": "$total" },
        "hobbies": {
            "$push": { "name": "$_id.hobby", "count": "$hobbyCount" }
        }
    }}
])

:

[
    {
            "_id" : "female",
            "total" : 1,
            "hobbies" : [
                {
                    "name" : "tennis",
                    "count" : 1
                },
                {
                    "name" : "football",
                    "count" : 1
                }
            ]
    },
    {
        "_id" : "male",
        "total" : 2,
        "hobbies" : [
            {
                "name" : "swimming",
                "count" : 1
            },
            {
                "name" : "tennis",
                "count" : 2
            },
            {
                "name" : "football",
                "count" : 2
            }
        ]
    }
]

, $group "" . , - $unwind , , $group, , , .

, , , MongoDB .

( - , , ), . JavaScript, :

var out = db.people.aggregate([
    { "$group": {
        "_id": "$sex",
        "hobbies": { "$push": "$hobbies" },
        "total": { "$sum": 1 }
    }},
    { "$unwind": "$hobbies" },
    { "$unwind": "$hobbies" },
    { "$group": {
        "_id": {
            "sex": "$_id",
            "hobby": "$hobbies"
        },
        "total": { "$first": "$total" },
        "hobbyCount": { "$sum": 1 }
    }},
    { "$group": {
        "_id": "$_id.sex",
        "total": { "$first": "$total" },
        "hobbies": {
            "$push": { "name": "$_id.hobby", "count": "$hobbyCount" }
        }
    }}
]).toArray();

out.forEach(function(doc) {
    var obj = {};
    doc.hobbies.sort(function(a,b) { return a.count < b.count });
    doc.hobbies.forEach(function(hobby) {
        obj[hobby.name] = hobby.count;
    });
    doc.hobbies = obj;
    printjson(doc);
});

, , :

{
    "_id" : "female",
    "total" : 1,
    "hobbies" : {
        "tennis" : 1,
        "football" : 1
    }
}
{
    "_id" : "male",
    "total" : 2,
    "hobbies" : {
        "tennis" : 2,
        "football" : 2,
        "swimming" : 1
    }
}

​​ , , .

, mapReduce:

db.people.mapReduce(
    function() {
        emit(
            this.sex,
            { 
                "total": 1,
                "hobbies": this.hobbies.map(function(key) {
                    return { "name": key, "count": 1 };
                })
            }
        );
    },
    function(key,values) {
        var obj  = {},
            reduced = {
                "total": 0,
                "hobbies": []
            };

        values.forEach(function(value) {
            reduced.total += value.total;
            value.hobbies.forEach(function(hobby) {
                if ( !obj.hasOwnProperty(hobby.name) )
                    obj[hobby.name] = 0;
                obj[hobby.name] += hobby.count;
            });
        });

        reduced.hobbies = Object.keys(obj).map(function(key) {
            return { "name": key, "count": obj[key] };
        }).sort(function(a,b) {
            return a.count < b.count;
        });

        return reduced;
    },
    { 
        "out": { "inline": 1 },
        "finalize": function(key,value) {
            var obj = {};
            value.hobbies.forEach(function(hobby) {
                obj[hobby.name] = hobby.count;
            });
            value.hobbies = obj;
            return value;
        }
    }
)

, mapReduce , , , :

   "results" : [
        {
            "_id" : "female",
            "value" : {
                "total" : 1,
                "hobbies" : {
                    "football" : 1,
                    "tennis" : 1
                }
            }
        },
        {
            "_id" : "male",
            "value" : {
                "total" : 2,
                "hobbies" : {
                    "football" : 2,
                    "tennis" : 2,
                    "swimming" : 1
                }
            }
        }
    ]

, , . , , , .