Mongo average aggregation query with no group

Question

I am trying to get the average of a whole field using the aggregation framework in Mongo. However i can\'t seem to find any example that uses it without a group parameter. <

Answer 1

For more details please visit the following link: https://docs.mongodb.com/manual/reference/operator/aggregation/group/index.html

db.EvaluatedSentiments.aggregate([
{
$group:{_id:null,avgbvc: {$avg:"$bvc"}}
}
]).forEach(printjson)

Answer 2

First of all store numerical values as numbers. Afterwards you can use a simple statement to calculate the average:

db.collection.aggregate({ 
  "$group": {
    "_id": null, 
    "avg_bvc": { "$avg": "$bvc" } 
  } 
})

You can simply use more $avg aggregation operators to get averages for your other numeric fields:

db.collection.aggregate({ 
  "$group": {
    "_id": null, 
    "avg_bvc": { "$avg": "$bvc" }, 
    "avg_dollar": { "$avg": "$dollar" } 
  } 
})

Answer 3

So if your data actually was numeric which is it not and your intention is to exclude the documents that have a "greater than zero" value then you include a $match statement in your aggregation pipeline in order to "filter" out these documents:

db.EvaluatedSentiments.aggregate([
    { "$match": {
        "bvc": { "$gt": 0 }
    }},
    { "$group": {
        "_id": null,
        "bvc": { "$avg": "$bvc" }
    }}
])