Combining series in a node

InfluxDB 1 Kapacitor
1

I have a node that looks like:

   "series" : [

      {
         "name" : "measurement_name",
         "columns" : [
            "time",
            "count"
         ]
         "values" : [
            [
               "2017-10-17T17:04:20Z",
               2
            ]
         ],
         "tags" : {
            "subject" : "a",
            "source" : "1"
         },
      },

      {
         "name" : "measurement_name",
         "columns" : [
            "time",
            "count"
         ],
         "values" : [
            [
               "2017-10-17T17:04:20Z",
               2
            ]
         ]
         "tags" : {
            "subject" : "a",
            "source" : "2"
         },
      }

   ]

What options do I have for combining points from these separate series? I’d like to average the “count” across each point with the same “subject” (and time, roughly). Or even just drop all but one series that have the same “subject”.