How to Group mongodb - mapReduce output?

Question

i have a query regarding the mapReduce framework in mongodb, so i have a result of key value pair from mapReduce function , now i want to run the query on this output of map

Answer 1

Try this,

db.order.mapReduce(function() { emit (this.customer,{count:1,orderDate:this.orderDate.interval_start}) },
function(key,values){ 
var category; // add this new field
var sum =0 ; var lastOrderDate;  
values.forEach(function(value) {
 if(value['orderDate']){ 
    lastOrderDate=value['orderDate'];
}  
sum+=value['count'];
}); 
// at this point you are already aware in which category your records lies , just add a new field to mark it
 if(sum < 5){ category: userLessThan5};
 if(sum >= 5 && sum <=10){ category: user5to10};
 if(sum <= 10 && sum >= 15){ category: user10to15};
 if(sum <= 15 && sum >=20){ category: user15to20};
  ....
return {count:sum,lastOrderDate:lastOrderDate,category:category}; 
},
{ query:{status:"DELIVERED"},out:"order_total"}).find()
 db.order_total.aggregate([{ $group: { "_id": "$value.category", "users": { $sum: 1 } } }]);

you will get you desired result

{userLessThan5: 9 }
{user5to10: 2 }
{user10to15: 1 }
{user15to20: 0 }
 ....

Answer 2

You could try to group the output data after mapreduce to every 5 interval count through aggregate like below

db.data.aggregate([
    { "$group": {
        "_id": {
            "$subtract": [
                { "$subtract": [ "$value.count", 0 ] },
                { "$mod": [ 
                    { "$subtract": [ "$value.count", 0 ] },
                    5
                ]}
            ]
        },
        "count": { "$sum": 1 }
    }}
])

Also maybe here is one related question here.

Answer 3

I wrote a query using your data in aggregation as per my knowledge, there may be better way to solve this problem.

var a=db.test.aggregate([{$match:{"value.count":{$lt:5}}},
              { $group: { _id:"$value.count",total:{"$sum":1}}},
             {$group:{_id:"less than 5",total:{$sum:"$total"}}}])              

var b=db.test.aggregate([{$match:{"value.count":{$lt:10,$gt:5}}},
            { $group: { _id:"$value.count",total:{"$sum":1}}},
            {$group:{_id:"between 5 and 10",total:{$sum:"$total"}}}])

var c=db.test.aggregate([{$match:{"value.count":{$lt:15,$gt:10}}},
       { $group: { _id:"$value.count",total:{"$sum":1}}},
       {$group:{_id:"between 10 and 15",total:{$sum:"$total"}}}])

insert a, b, c into another collection