Elasticsearch nested aggregation ratios using nested and root level data

Question

I have what feels like a simple aggregation. I have a document that\'s timing code like so:

{
  \"task_start\": \"2020-06-03T21:19:07.908821Z\",
  \"task_end         


        

Answer 1

This one's tricky -- already discussed here.

I think you'll have to resort a bit of scripted_metrics and some method mocking because the exposed painless API is somewhat limited:

{
  "size": 0, 
  "aggs": {
    "task_metrics_median": {
      "scripted_metric": {
        "init_script": "state.ratios = new ArrayList();",

        "map_script": """
          // access the source incl. the nested subtasks
          def d = params._source;

          for (def subtask : d.sub_tasks) {
            // mimicking a `term` query
            if (subtask.key != 'sub-task1-time-milliseconds') break;

            // incoming as strings so parse
            def millis_end = ZonedDateTime.parse(d.task_end).toInstant().toEpochMilli();
            def millis_start = ZonedDateTime.parse(d.task_start).toInstant().toEpochMilli();

            double task_time = (millis_end - millis_start);

            // prevent zero division
            if (task_time <= 0) break;

            state['ratios'].add(subtask.value / task_time);  
          }
        """,

        "combine_script": """
            def ratios = state.ratios;
            Collections.sort(ratios);

            // trivial median calc
            double median;
            if (ratios.length % 2 == 0) {
                median = ((double)ratios[ratios.length/2] + (double)ratios[ratios.length/2 - 1])/2;
            } else {
                median = (double) ratios[ratios.length/2];
            }

            return median
        """,

        "reduce_script": "return states"
      }
    }
  }
}