summation of two columns in Aggregate Method

Question

I am using mongodb Aggregate query. My db is like this:

{
  \"_id\" : ObjectId(\"5a81636f017e441d609283cc\"),
  \"userid\": \"123\",
  page : \'A\',
  newpage: \         


        

Answer 1

There you go:

db.Collection.aggregate([
    {$match:{ "userid":"123"}}, // filter out what's not of interest
    {$facet: { // process two stages in parallel --> this will give us a single result document with the following two fields
        "newpage": [ // "newpage" holding the ids and sums per "newpage" field
            {$group:{"_id":"$newpage", "count":{"$sum":1}}}
        ],
        "page": [ // and "page" holding the ids and sums per "page" field
            {$group:{"_id":"$page", "count":{"$sum":1}}}
        ]
    }},
    {$project: {x:{$concatArrays:["$newpage", "$page"]}}}, // merge the two arrays into one
    {$unwind: "$x"}, // flatten the single result document into multiple ones so we do not need to $reduce but can nicely $group
    {$group: {_id: "$x._id", "count": {$sum: "$x.count"}}} // perform the final grouping/counting,
    {$sort: {count: -1}} // well, the sort according to your question
]);