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How to speed up $group phase in aggregation?
To speed up the $group phase, use $group along with aggregation. Let us see an example and create a collection with documents −
> db.demo423.insertOne({"Information":[101,110,87,110,98,115,101,115,89,115]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e73a60e9822da45b30346e6")
}Display all documents from a collection with the help of find() method −
> db.demo423.find();
This will produce the following output −
{ "_id" : ObjectId("5e73a60e9822da45b30346e6"), "Information" : [ 101, 110, 87, 110, 98, 115, 101, 115, 89, 115 ] }Following is the query to speed up $group phase in aggregation −
> db.demo423.aggregate([
... {
... $project: {_id: 0, 'Information': 1}
... },
... {
... $unwind: '$Information'
... },
... {
... $group:{_id: '$Information', frequency:{$sum: 1}}
... },
... {
... $sort:{frequency:-1}
... },
... {
... $limit:2
... }
... ])This will produce the following output −
{ "_id" : 115, "frequency" : 3 }
{ "_id" : 110, "frequency" : 2 }
Updated on: 03-Apr-2020
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