Create Price Range in mongo with aggregation pipeline with Nodejs

Question

Wan't create Price range Using mongodb aggregation pipeline.. while using elastic search or solr we can directly get price filter range value... How can i create price range according to my products price, if there is no product in that range then don't create that range...

{ 
    "_id" : ObjectId("5657412ddb70397479575d1d"),"price" : 1200
},
{ 
    "_id" : ObjectId("5657412ddb70397479575d1d"),"price" : 200
},
{ 
    "_id" : ObjectId("5657412ddb70397479575d1d"),"price" : 2000
},
{ 
    "_id" : ObjectId("5657412ddb70397479575d1d"),"price" : 2020
},
{ 
    "_id" : ObjectId("5657412ddb70397479575d1d"),"price" : 100
},
{ 
    "_id" : ObjectId("5657412ddb70397479575d1d"),"price" : 3500
},
{ 
    "_id" : ObjectId("5657412ddb70397479575d1d"),"price" : 3900
}

From above i have to create price range as par product price like filter available in flipkart OR myntra using Mongo aggregation...

[
        {
            range : '100-200',
            count : 2
        },
        {
            range : '1200-2020',
            count : 3
        },
        {
            range : '3500-3900',
            count : 2
        }

]

Answer 1

Within the aggregation framework pipeline, you can take advantage of the $cond operator in the $project stage to create an extra field that denotes the range the price falls in, and then use the $group step to get the counts:

var pipeline = [    
    {
        "$project": {
            "price": 1,
            "range": {
                "$cond": [ 
                    {
                        "$and": [
                            { "$gte": ["$price", 100] },
                            { "$lte": ["$price", 200] }
                        ]
                    }, 
                    "100-200", 
                    {
                        "$cond": [ 
                            {
                                "$and": [
                                    { "$gte": ["$price", 1200] },
                                    { "$lte": ["$price", 2020] }
                                ]
                            }, 
                            "1200-2020", "2021-above" 
                        ]
                    }
                ]
            }
        }
    },
    { 
        "$group": { 
            "_id": "$range",             
            "count": { "$sum": 1 }
        }  
    },
    {
        "$project": {
            "_id": 0,             
            "range": "$_id",
            "count": 1

        }
    }
];

collection.aggregate(pipeline, function (err, result){
     if (err) {/* Handle err */};
     console.log(JSON.stringify(result, null, 4));
});