Grouping the array items in MongoDB and get the count the products with similar price?

To group the array items, use $group along with $sort. Let us create a collection with documents −

> db.demo566.insertOne(
... {
...
...    "ProductInformation" : [
...       {
...          "ProductName" : "Product-1",
...          "ProductPrice" :100
...       },
...       {
...          "ProductName" : "Product-2",
...          "ProductPrice" :1100
...       },
...       {
...          "ProductName" : "Product-3",
...          "ProductPrice" :100
...       },
...       {
...          "ProductName" : "Product-4",
...          "ProductPrice" :1100
...       },
...       {
...          "ProductName" : "Product-5",
...          "ProductPrice" :100
...       }
...    ]
...
... }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e908e2339cfeaaf0b97b57a")
}

Display all documents from a collection with the help of find() method −

> db.demo566.find();

This will produce the following output −

{ "_id" : ObjectId("5e908e2339cfeaaf0b97b57a"), "ProductInformation" : [
   { "ProductName" : "Product-1", "ProductPrice" : 100 },
   { "ProductName" : "Product-2", "ProductPrice" : 1100 },
   { "ProductName" : "Product-3", "ProductPrice" : 100 },
   { "ProductName" : "Product-4", "ProductPrice" : 1100 },
   { "ProductName" : "Product-5", "ProductPrice" : 100 } 
] }

Following is the query to group the array items −

> db.demo566.aggregate([
... {
...    "$unwind": "$ProductInformation"
... },
... {
...    "$group": {
...       "_id": "$ProductInformation.ProductPrice",
...       "Value": { "$sum" : 1 }
...    }
... },
... { "$sort": { "_id" :1 } }
... ])

This will produce the following output −

{ "_id" : 100, "Value" : 3 }
{ "_id" : 1100, "Value" : 2 }