[Backport 7.9] Add standard deviation / variance sampling to extended stats

src/Nest/Aggregations/AggregateFormatter.cs

@@ -72,7 +72,11 @@ internal class AggregateFormatter : IJsonFormatter<IAggregate>
 		{
 			{ "variance", 0 },
 			{ "std_deviation", 1 },
-			{ "std_deviation_bounds", 2 }
+			{ "std_deviation_bounds", 2 },
+			{ "variance_population", 3 },
+			{ "variance_sampling", 4 },
+			{ "std_deviation_population", 5 },
+			{ "std_deviation_sampling", 6 },
 		};
 
 		private static readonly byte[] ValueAsStringField = JsonWriter.GetEncodedPropertyNameWithoutQuotation(Parser.ValueAsString);
@@ -589,6 +593,18 @@ private IAggregate GetExtendedStatsAggregate(ref JsonReader reader, IJsonFormatt
 							extendedStatsMetric.StdDeviationBounds =
 								formatterResolver.GetFormatter<StandardDeviationBounds>().Deserialize(ref reader, formatterResolver);
 							break;
+						case 3:
+							extendedStatsMetric.VariancePopulation = reader.ReadNullableDouble();
+							break;
+						case 4:
+							extendedStatsMetric.VarianceSampling = reader.ReadNullableDouble();
+							break;
+						case 5:
+							extendedStatsMetric.StdDeviationPopulation = reader.ReadNullableDouble();
+							break;
+						case 6:
+							extendedStatsMetric.StdDeviationSampling = reader.ReadNullableDouble();
+							break;
 					}
 				}
 				else

src/Nest/Aggregations/Metric/ExtendedStats/ExtendedStatsAggregate.cs

@@ -8,10 +8,53 @@ namespace Nest
 {
 	public class ExtendedStatsAggregate : StatsAggregate
 	{
+		/// <summary>
+		/// The standard deviation of the collected values
+		/// </summary>
 		public double? StdDeviation { get; set; }
+
+		/// <summary>
+		/// The upper or lower bounds of standard deviation
+		/// </summary>
 		public StandardDeviationBounds StdDeviationBounds { get; set; }
+
+		/// <summary>
+		/// The sum of squares of the collected values
+		/// </summary>
 		public double? SumOfSquares { get; set; }
+
+		/// <summary>
+		/// The variance of the collected values
+		/// </summary>
 		public double? Variance { get; set; }
+
+		/// <summary>
+		/// The population variance of the collected values.
+		/// <para />
+		/// Valid in Elasticsearch 7.9.0+
+		/// </summary>
+		public double? VariancePopulation { get; set; }
+
+		/// <summary>
+		/// The sampling variance of the collected values.
+		/// <para />
+		/// Valid in Elasticsearch 7.9.0+
+		/// </summary>
+		public double? VarianceSampling { get; set; }
+
+		/// <summary>
+		/// The population standard deviation of the collected values.
+		/// <para />
+		/// Valid in Elasticsearch 7.9.0+
+		/// </summary>
+		public double? StdDeviationPopulation { get; set; }
+
+		/// <summary>
+		/// The sampling standard deviation of the collected values.
+		/// <para />
+		/// Valid in Elasticsearch 7.9.0+
+		/// </summary>
+		public double? StdDeviationSampling { get; set; }
 	}
 
 	[DataContract]
@@ -22,5 +65,17 @@ public class StandardDeviationBounds
 
 		[DataMember(Name = "upper")]
 		public double? Upper { get; set; }
+
+		[DataMember(Name = "lower_population")]
+		public double? LowerPopulation { get; set; }
+
+		[DataMember(Name = "upper_population")]
+		public double? UpperPopulation { get; set; }
+
+		[DataMember(Name = "lower_sampling")]
+		public double? LowerSampling { get; set; }
+
+		[DataMember(Name = "upper_sampling")]
+		public double? UpperSampling { get; set; }
 	}
 }

tests/Tests/Aggregations/Metric/ExtendedStats/ExtendedStatsAggregationUsageTests.cs

@@ -2,9 +2,10 @@
 // Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information
 
-using System;
+using System;
 using FluentAssertions;
 using Nest;
+using Tests.Core.Client;
 using Tests.Core.Extensions;
 using Tests.Core.ManagedElasticsearch.Clusters;
 using Tests.Domain;
@@ -56,6 +57,19 @@ protected override void ExpectResponse(ISearchResponse<Project> response)
 			commitStats.StdDeviationBounds.Should().NotBeNull();
 			commitStats.StdDeviationBounds.Upper.Should().BeGreaterThan(0);
 			commitStats.StdDeviationBounds.Lower.Should().NotBe(0);
+
+			// hide
+			if (TestClient.Configuration.InRange(">=7.9.0"))
+			{
+				commitStats.VariancePopulation.Should().BeGreaterThan(0);
+				commitStats.VarianceSampling.Should().BeGreaterThan(0);
+				commitStats.StdDeviationPopulation.Should().BeGreaterThan(0);
+				commitStats.StdDeviationSampling.Should().BeGreaterThan(0);
+				commitStats.StdDeviationBounds.UpperPopulation.Should().BeGreaterThan(0);
+				commitStats.StdDeviationBounds.UpperSampling.Should().NotBe(0);
+				commitStats.StdDeviationBounds.LowerPopulation.Should().NotBe(0);
+				commitStats.StdDeviationBounds.LowerSampling.Should().NotBe(0);
+			}
 		}
 	}