Serial Differencing Aggregation Usageedit

Fluent DSL exampleedit

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)
        )
        .SerialDifferencing("second_difference", d => d
            .BucketsPath("commits")
            .Lag(2)
        )
    )
)

Object Initializer syntax exampleedit

new DateHistogramAggregation("projects_started_per_month")
{
    Field = "startedOn",
    Interval = DateInterval.Month,
    Aggregations =
        new SumAggregation("commits", "numberOfCommits")
        && new SerialDifferencingAggregation("second_difference", "commits")
        {
            Lag = 2
        }
}

Example json output. 

{
  "projects_started_per_month": {
    "date_histogram": {
      "field": "startedOn",
      "interval": "month"
    },
    "aggs": {
      "commits": {
        "sum": {
          "field": "numberOfCommits"
        }
      },
      "second_difference": {
        "serial_diff": {
          "buckets_path": "commits",
          "lag": 2
        }
      }
    }
  }
}

Handling Responsesedit

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 differenceCount = 0;

foreach (var item in projectsPerMonth.Buckets)
{
    differenceCount++;
    var commits = item.Sum("commits");
    commits.Should().NotBeNull();
    commits.Value.Should().NotBe(null);

    var secondDifference = item.SerialDifferencing("second_difference");

    // serial differencing specified a lag of 2, so
    // only expect values from the 3rd bucket onwards
    if (differenceCount <= 2)
    {
        secondDifference.Should().BeNull();
    }
    else
    {
        secondDifference.Should().NotBeNull();
        secondDifference.Value.Should().NotBe(null);
    }
}