Cloudant built in function for sum count and stats

Built-in reduces

While you can define your own reduce functions, it's often the case that your reduce is going to be doing a simple count or sum operation. There are a handful of built in reduce functions; _sum, _count and _stats. If you can use these functions you should - they're faster than a javascript reduce (since they avoid serialisation between erlang and javascript) and are very well tested.

_sum

Produces the sum of all values for a key, values must be numeric

_count

Produces the row count for a given key, values can be any valid json

_stats

Produces a json structure containing sum, count, min, max and sum squared, values must be numeric

To use a built-in reduce, just put its name in place of the javascript reduce function inside your view.

{
    "_id": "_design/views103",
    "_rev": "8-1798b34c9929eb36d3bc04f99d2b5445",
    "indexes": {
        "animals": {
            "index":
                "function(doc){\n
                    index(\"default\", doc._id);\n\n
                    if (doc['customerID']){\n    index(\"customerID\", doc['customerID'], {\"store\": \"yes\"});\n  }\n\n
                    if (doc['trxnStatus']){\n    index(\"trxnStatus\", doc['trxnStatus'], {\"store\": \"yes\"});\n  }\n\n
                    if (doc['createdStamp']){\n    index(\"createdStamp\", doc['createdStamp'], {\"store\": \"yes\"});\n  }\n\n
                    if (doc['paymentType']){\n    index(\"paymentType\", doc['paymentType'], {\"store\": \"yes\"});\n  }\n\n
                    if (doc['returnAmount']){\n    index(\"returnAmount\", doc['returnAmount'], {\"store\": \"yes\"});\n  }\n\n
                    if (doc['trxnNumber']){\n    index(\"trxnNumber\", doc['trxnNumber'], {\"store\": \"yes\"});\n  }\n\n
                    if (doc['trxnReference']){\n    index(\"trxnReference\", doc['trxnReference'], {\"store\": \"yes\"});\n  }\n\n
                    if (doc['authCode']){\n    index(\"authCode\", doc['authCode'], {\"store\": \"yes\"});\n
                }\n\n
            }"
        }
    },
    "views": {
        "returnAmount_sum": {
            "map": "function(doc) {\n  if(doc.returnAmount && doc.customerID){\n    emit(doc.customerID, doc.returnAmount);\n  }\n}",
            "reduce": "function (keys, values, rereduce) {\nreturn (values);\n}"
        }
    }
}

https://pritom.cloudant.com/transactions/_design/views103/_view/returnAmount_sum
https://cloudant.com/for-developers/views/#pageArea 

{
  "_id": "_design/name",
  "views": {
    "view1": {
      "map":"function(doc){emit(doc.field, 1)}",
      "reduce": "function(key, value, rereduce){return sum(values)}"
    }
  }
}