How to emit more than two parameters using MongoDB MapReduce

[munavar fairooz]

I have a collection called 'orders' having lot of documents of the form

{
     _id: 123
     cust_id: "abc123",
     ord_date: new Date("Oct 04, 2012"),
     status: 'A',
     price: 25,
   
}

Now i want to
emit(cust_id, Price,_id) through map function .
Here

 Cust_id =>Key
 Price =>value
 _Id => Provenance Parameter

    In the Reduce function i will find the total Price of each cust_id and also , i want to store the  _id values of the documents that contributed to the total price of each cust_id into a separate  Provenance collection.
Map Reduce function support only 2 arguments. Is there any way to solve the problem??

Thank you....

[Asya Kamsky]

The second argument can be a document, so emit something like

{price: this.price, _id: [ this._id ] }

You will need to adjust your reduce to return the same type, so I assume you want eventually a list of _id's, you need to emit an  array.

Asya

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[Asya Kamsky]

The problem is your reduce function.

When you have an array values of this form:

[  { price: 15, _id: [ ObjectId("...") ] }, { price: 27, _id: [ ObjectId("...") ] } ]

You cannot reduce that to a single { price: xxx, _id: [ ..., ..., ...] } the way you are doing, you will actually need to iterate over values array accumulating prices and concatenating arrays elements.

Asya

 

On Mon, Feb 16, 2015 at 12:58 AM, munavar fairooz <m4mu...@gmail.com> wrote:

Sir,
what i want in the result collection is

{_id:cust_id,
value: {total: sum(price), id:[array of id's corresponding documents]}
}

As you said, i have written my Map function as

var mapFunction1 = function() {
                       emit(this.cust_id, {price:this.price, _id: [ this._id ]})
                   };
var reduceFunction1 = function(keyCustId, value) {
                         
                          return {total:Array.sum(value['price']), id:Array([value['_id']])};
                      };
db.order.mapReduce( mapFunction1,reduceFunction1,{ out: "map_reduce_example" });

But its showing an error like
 Error: map reduce failed:{
    "errmsg" : "exception: TypeError: Cannot read property 'length' of undefined\n    at Function.Array.sum (src/mongo/shell/types.js:192:12)\n    at _funcs2 (_funcs2:3:47) at src/mongo/shell/types.js:192",
    "code" : 16722,
    "ok" : 0
}
    at Error (<anonymous>)
    at DBCollection.mapReduce (src/mongo/shell/collection.js:1227:15)
    at (shell):1:10 at src/mongo/shell/collection.js:1227


Whats wrong with the program??
thankyou....

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