Average of data in OIC mapper

Content

Hi Experts,

Below is the data coming from the source system. Would like to calculate the average of Rating of the same account name. Can you please help you this can be achieved. 

{

    "Contacts": [{

            "Id": "abc",

            "AccountName": "apple",

            "Rating":"4",

          

            

        },

        {

            "Id": "xyz",

            "AccountName": "apple",

            "Rating":"3.5",

           

           

        },

{

            "Id": "ddd",

            "AccountName": "google",

            "Rating":"4",

           

           

        },{

            "Id": "xyz",

            "AccountName": "google",

            "Rating":"2",

           

           

        }

    ]

}