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Derivative Aggregation Usage

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Derivative Aggregation Usage

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Fluent DSL example

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a => a
.DateHistogram("projects_started_per_month", dh => dh
    .Field(p => p.StartedOn)
    .Interval(DateInterval.Month)
    .Aggregations(aa => aa
        .Sum("commits", sm => sm
            .Field(p => p.NumberOfCommits)
        )
        .Derivative("commits_derivative", d => d
            .BucketsPath("commits")
        )
    )
)

Object Initializer syntax example

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new DateHistogramAggregation("projects_started_per_month")
{
    Field = "startedOn",
    Interval = DateInterval.Month,
    Aggregations =
        new SumAggregation("commits", "numberOfCommits") &&
        new DerivativeAggregation("commits_derivative", "commits")
}

Example json output.

{
  "projects_started_per_month": {
    "date_histogram": {
      "field": "startedOn",
      "interval": "month"
    },
    "aggs": {
      "commits": {
        "sum": {
          "field": "numberOfCommits"
        }
      },
      "commits_derivative": {
        "derivative": {
          "buckets_path": "commits"
        }
      }
    }
  }
}

Handling Responses

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response.ShouldBeValid();

var projectsPerMonth = response.Aggregations.DateHistogram("projects_started_per_month");
projectsPerMonth.Should().NotBeNull();
projectsPerMonth.Buckets.Should().NotBeNull();
projectsPerMonth.Buckets.Count.Should().BeGreaterThan(0);

var notNullDerivativeSeen = 0;
// derivative not calculated for the first bucket
foreach (var item in projectsPerMonth.Buckets.Skip(1))
{
    if (item.DocCount == 0) continue;
    var commitsDerivative = item.Derivative("commits_derivative");
    commitsDerivative.Should().NotBeNull();
    if (commitsDerivative.Value != null) notNullDerivativeSeen++;
}
notNullDerivativeSeen.Should().BeGreaterThan(0, "atleast one bucket should yield a derivative value surely!");

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