group operations over arrays using Mongo aggregation framework

Question

I'm using mongodb 2.2. I would like to use the new Aggregation Framework to do queries over my documents, but the elements are arrays.

Here an example of my $project result:

{ 
  "type" : [
      "ads-get-yyy",
      "ads-get-zzz"
  ],
  "count" : [
      NumberLong(0),
      NumberLong(10)
  ],
  "latency" : [
      0.9790918827056885,
      0.9790918827056885
  ]
}

I want to group by type, so for "ads-get-yyy" to know how much is the average of count and how much is the average of the latency.

I would like to have something similar to the next query, but that works inside of the elements of every array:

db.test.aggregate(
{
  $project : {
    "type" : 1,
    "count" : 1,
    "latency" : 1
  }
},{
  $group : {
    _id: {type : "$type"},
    count: {$avg: "$count"},
    latency: {$avg: "$latency"}
  }
});

Nic Cottrell · Accepted Answer · 2012-09-20 13:12:27Z

1

I'm just learning the new AF too, but I think you need to first $unwind the types so that you can group by them. So something like:

db.test.aggregate({
  $project : {
    "type" : 1,
    "count" : 1,
    "latency" : 1
  }
},{
  $unwind : "$type"
},{
  $group : {
    _id: {type : "$type"},
    count: {$avg: "$count"},
    latency: {$avg: "$latency"}
  }
});

answered Sep 20, 2012 at 13:12

Nic Cottrell

9,7457 gold badges57 silver badges82 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

group operations over arrays using Mongo aggregation framework

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related