Aggregation - Percentage

[Andrés]

Hello,

I have a collection with following documents:

{idnumber: "5324", colour: "red"}
{idnumber: "9435", colour: "blue"}
{idnumber: "4323", colour: "yellow"}
{idnumber: "3123", colour: "red"}
{idnumber: "2220", colour: "blue"}
{idnumber: "6456", colour: "blue"}

I am looking to get percentage of colours, something like this:

blue	50,000000%
red	33,333333%
yellow	16,666667%

Any suggestions?

Thank you!

[Andrés]

I have managed to calculate percentages, but I still have a step missisng ...

I need to calculate the total number of documents (in yellow) inside the [], inside the "aggregation" operation.

 

[

        { "$group": { "_id": {"colour":  "$colour"}, "count": { "$sum": 1 }}},   

        { "$project": {

            "count": 1,

            "percentage": {

                "$concat": [ { "$substr": [ { "$multiply": [ { "$divide": [ "$count", 6 ] }, 100 ] }, 0,4 ] }, "", "%" ]}

            }

        }

    ]

That is what is supposed to do, but I can not do it. because where I am working, I can only type "aggregation" operations:

var total = db.mycollection.count ()

 

[

        { "$group": { "_id": {"colour":  "$colour"}, "count": { "$sum": 1 }}},   

        { "$project": {

            "count": 1,

            "percentage": {

                "$concat": [ { "$substr": [ { "$multiply": [ { "$divide": [ "$count", total ] }, 100 ] }, 0,4 ] }, "", "%" ]}

            }

        }

    ]

So, I would like to know whether I can calculate the TOTAL inside the []

Thanks!

[Asya Kamsky]

You can calculate the total in aggregation using $group on _id null but you would need to preserve all the color details and then unwind them to calculate percentages.  It would probably be simpler to do it the way you are doing it now.

I'm not sure what you mean when you say you can only type aggregation - why can't you do a simple count on the collection first?

Asya

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[Pankaj Saraswat]

How about this?

db.pankaj.aggregate([
    {$group:{
        "_id":"",
        "total":{$sum:1},
        "color set":{$push:"$color"}}},
    {$unwind:"$color set"},
    {$group:{
        "_id":{"color":"$color set","total":"$total"},

        "count":{$sum:1}}},
    {$project:{

        "_id":{"color":"$_id.color"},
        "weight":{$multiply:[{$divide:["$count","$_id.total"]},100]}}}
    ])