Map reduce | Grouping on resopnse of map function and show count

Couchbase Server
,
1

Hi, the response of my map function is:

key:

[ 1525132800000, 1525152600000 ]

The date fields in the above key are: startDateEpoch and lastModifiedDateEpoch

value:

{
  "propertyId": "DAWN",
  "startDate": "2018-05-01",
  "endDate": "2018-05-04",
  "verificationStatusCode": "ICMO"
}

In Key, there are two date fields which are used for filtering out the required result set.
I want to get the counts of docs after grouping them on all the fields available in the response of map function. I am not able to write reduce function for this. Any suggestion on how it can be done?

The response from the reduce function I want is:

{
  "propertyId": "DAWN",
  "startDate": "2018-05-01",
  "endDate": "2018-05-04",
  "verificationStatusCode": "ICMO", 
 "count":54
}