From 7973d45a92d6625bc6a40bdd10331d820b49c994 Mon Sep 17 00:00:00 2001
From: dfinke <finked@hotmail.com>
Date: Sun, 1 Oct 2017 13:05:55 -0400
Subject: [PATCH 01/19] First pass at adding std deviation to measure-object

---
 .../commands/utility/Measure-Object.cs        | 56 ++++++++++++++++++-
 .../Measure-Object.Tests.ps1                  | 22 ++++++++
 2 files changed, 76 insertions(+), 2 deletions(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index 0a16b3a3155..45c4e85eb6a 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -34,7 +34,7 @@ public sealed class GenericMeasureInfo : MeasureInfo
         /// </summary>
         public GenericMeasureInfo()
         {
-            Average = Sum = Maximum = Minimum = null;
+            Average = Sum = Maximum = Minimum = StdDeviation = null;
         }
 
         /// <summary>
@@ -71,6 +71,13 @@ public GenericMeasureInfo()
         ///
         /// </summary>
         public double? Minimum { get; set; }
+
+        /// <summary>
+        ///
+        /// The StdDeviation of property values
+        ///
+        /// </summary>
+        public double? StdDeviation { get; set; }
     }
 
     /// <summary>
@@ -90,7 +97,7 @@ public sealed class GenericObjectMeasureInfo : MeasureInfo
         /// </summary>
         public GenericObjectMeasureInfo()
         {
-            Average = Sum = null;
+            Average = Sum = StdDeviation = null;
             Maximum = Minimum = null;
         }
 
@@ -128,6 +135,13 @@ public GenericObjectMeasureInfo()
         ///
         /// </summary>
         public object Minimum { get; set; }
+
+        /// <summary>
+        ///
+        /// The StdDeviation of property values
+        ///
+        /// </summary>
+        public double? StdDeviation { get; set; }
     }
 
     /// <summary>
@@ -225,6 +239,8 @@ private class Statistics
 
             // Generic/Numeric statistics
             internal double sum = 0.0;
+            internal double stdDeviation = 0.0;
+            internal List<double> stdDeviationNumbers = new List<double>();
             internal object max = null;
             internal object min = null;
 
@@ -263,6 +279,25 @@ public MeasureObjectCommand()
 
         #endregion Common parameters in both sets
 
+        /// <summary>
+        /// Set to true is StdDeviation is to be returned
+        /// </summary>
+        /// <value></value>
+        [Parameter(ParameterSetName = GenericParameterSet)]
+        public SwitchParameter StdDeviation
+        {
+            get
+            {
+                return _measureStdDeviation;
+            }
+            set
+            {
+                _measureStdDeviation = value;
+            }
+        }
+
+        private bool _measureStdDeviation;
+
         /// <summary>
         /// Set to true is Sum is to be returned
         /// </summary>
@@ -710,6 +745,8 @@ private void AnalyzeNumber(double numValue, Statistics stat)
         {
             if (_measureSum || _measureAverage)
                 stat.sum += numValue;
+            if (_measureStdDeviation)
+                stat.stdDeviationNumbers.Add(numValue);
         }
 
         /// <summary>
@@ -790,6 +827,7 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
         {
             double? sum = null;
             double? average = null;
+            double? stdDeviation = null;
             object max = null;
             object min = null;
 
@@ -797,8 +835,21 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
             {
                 if (_measureSum)
                     sum = stat.sum;
+
                 if (_measureAverage && stat.count > 0)
                     average = stat.sum / stat.count;
+
+                if (_measureStdDeviation && _measureAverage && stat.count > 0)
+                {
+                    var popdev = 0.0;
+
+                    foreach (double n in stat.stdDeviationNumbers)
+                    {
+                        popdev += Math.Pow((n - (double)average), 2);
+                    }
+
+                    stdDeviation = Math.Round(Math.Sqrt(popdev / (stat.stdDeviationNumbers.Count - 1)), 4);
+                }
             }
 
             if (_measureMax)
@@ -835,6 +886,7 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
                 gmi.Count = stat.count;
                 gmi.Sum = sum;
                 gmi.Average = average;
+                gmi.StdDeviation = stdDeviation;
                 if (null != max)
                 {
                     gmi.Maximum = (double)max;
diff --git a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1 b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
index 6791d790a1a..9674b384a11 100644
--- a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
+++ b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
@@ -17,6 +17,28 @@ Describe "Measure-Object" -Tags "CI" {
         $($testObject | Measure-Object).Count | Should Be $testObject.Length
     }
 
+
+    It "Should calculate Standard Deviation" {
+        $actual = ($testObject | Measure-Object -Average -StdDeviation)
+        $actual.StdDeviation | Should Be 1.5275
+    }
+
+    It "Should throw if Standard Deviation with -Average not specified" {
+        #{$testObject | Measure-Object -StdDeviation} | Should Throw
+        $actual = $testObject | Measure-Object -StdDeviation
+        $actual.StdDeviation | Should Be 1.5275
+    }
+
+    It 'Should throw if Standard Deviation requested and -Average:$false' {
+        try {
+            $Error.Clear()
+            $testObject | Measure-Object -StdDeviation -Average:$false -ErrorAction Stop
+        }
+        catch {
+            $Error.Count | should be 1
+        }
+    }
+
     It "Should be able to count using the Property switch" {
         $expected = $(Get-ChildItem $TestDrive).Length
         $actual   = $(Get-ChildItem $TestDrive | Measure-Object -Property Length).Count

From ea0cc8c16462f2562429057e0c1858e40efe97fa Mon Sep 17 00:00:00 2001
From: dfinke <finked@hotmail.com>
Date: Mon, 2 Oct 2017 16:48:05 -0400
Subject: [PATCH 02/19] Use A*A instead of Math.Pow. Throw if -Average not
 specified and fixed comments

---
 .../commands/utility/Measure-Object.cs         | 18 ++++++++++++------
 .../Measure-Object.Tests.ps1                   |  1 -
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index 45c4e85eb6a..5782e316d29 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -74,7 +74,7 @@ public GenericMeasureInfo()
 
         /// <summary>
         ///
-        /// The StdDeviation of property values
+        /// The Standard Deviation of property values
         ///
         /// </summary>
         public double? StdDeviation { get; set; }
@@ -138,7 +138,7 @@ public GenericObjectMeasureInfo()
 
         /// <summary>
         ///
-        /// The StdDeviation of property values
+        /// The Standard Deviation of property values
         ///
         /// </summary>
         public double? StdDeviation { get; set; }
@@ -280,7 +280,7 @@ public MeasureObjectCommand()
         #endregion Common parameters in both sets
 
         /// <summary>
-        /// Set to true is StdDeviation is to be returned
+        /// Set to true if Standard Deviation is to be returned
         /// </summary>
         /// <value></value>
         [Parameter(ParameterSetName = GenericParameterSet)]
@@ -839,16 +839,22 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
                 if (_measureAverage && stat.count > 0)
                     average = stat.sum / stat.count;
 
+                if(_measureStdDeviation && !_measureAverage) {
+                    var message = "StdDeviation was requested and requires the average to be calculated, please add the -Average switch";
+                    throw new ArgumentException(message);
+                }
+
                 if (_measureStdDeviation && _measureAverage && stat.count > 0)
                 {
-                    var popdev = 0.0;
+                    var sumOfDerivation = 0.0;
 
                     foreach (double n in stat.stdDeviationNumbers)
                     {
-                        popdev += Math.Pow((n - (double)average), 2);
+                        var m = n - (double)average;
+                        sumOfDerivation += m * m;
                     }
 
-                    stdDeviation = Math.Round(Math.Sqrt(popdev / (stat.stdDeviationNumbers.Count - 1)), 4);
+                    stdDeviation = Math.Round(Math.Sqrt(sumOfDerivation / (stat.stdDeviationNumbers.Count - 1)), 4);
                 }
             }
 
diff --git a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1 b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
index 9674b384a11..6296f3466a9 100644
--- a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
+++ b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
@@ -17,7 +17,6 @@ Describe "Measure-Object" -Tags "CI" {
         $($testObject | Measure-Object).Count | Should Be $testObject.Length
     }
 
-
     It "Should calculate Standard Deviation" {
         $actual = ($testObject | Measure-Object -Average -StdDeviation)
         $actual.StdDeviation | Should Be 1.5275

From b68253c9edb0c1e435ddc4626d488630ceba4620 Mon Sep 17 00:00:00 2001
From: dfinke <finked@hotmail.com>
Date: Mon, 2 Oct 2017 19:32:36 -0400
Subject: [PATCH 03/19] Added message to the rex file

---
 .../commands/utility/Measure-Object.cs                 | 10 ++++++++--
 .../resources/MeasureObjectStrings.resx                |  3 +++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index 5782e316d29..4dbeaa5406d 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -840,8 +840,14 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
                     average = stat.sum / stat.count;
 
                 if(_measureStdDeviation && !_measureAverage) {
-                    var message = "StdDeviation was requested and requires the average to be calculated, please add the -Average switch";
-                    throw new ArgumentException(message);
+                    ErrorRecord errorRecord = new ErrorRecord(
+                        PSTraceSource.NewArgumentException("Average"),
+                        "AverageSwitchNotSet",
+                        ErrorCategory.InvalidArgument,
+                        null);
+
+                    errorRecord.ErrorDetails = new ErrorDetails(this, "MeasureObjectStrings", "AverageSwitchNotSet", "Average");
+                    WriteError(errorRecord);
                 }
 
                 if (_measureStdDeviation && _measureAverage && stat.count > 0)
diff --git a/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx b/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx
index 8211114c335..c5c624771ac 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx
+++ b/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx
@@ -126,4 +126,7 @@
   <data name="NonNumericInputObject" xml:space="preserve">
     <value>Input object "{0}" is not numeric.</value>
   </data>
+  <data name="AverageSwitchNotSet" xml:space="preserve">
+    <value>StdDeviation was requested and requires the average to be calculated, please add the -Average switch.</value>
+  </data>
 </root>

From df488a3aa09dfbdcc0e5d99c02392de91207119a Mon Sep 17 00:00:00 2001
From: dfinke <finked@hotmail.com>
Date: Tue, 3 Oct 2017 13:53:11 -0400
Subject: [PATCH 04/19] Set Average true if StdDeviation is set

---
 .../commands/utility/Measure-Object.cs                          | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index 4dbeaa5406d..e99ad3e5a6e 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -293,6 +293,8 @@ public SwitchParameter StdDeviation
             set
             {
                 _measureStdDeviation = value;
+                if(value == true)
+                    _measureAverage = true;
             }
         }
 

From 515fb010f70e5fcef1e95e5e05bb32b7187e537c Mon Sep 17 00:00:00 2001
From: dfinke <finked@hotmail.com>
Date: Tue, 3 Oct 2017 13:53:19 -0400
Subject: [PATCH 05/19] Update message

---
 .../resources/MeasureObjectStrings.resx                         | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx b/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx
index c5c624771ac..bccbd5db10c 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx
+++ b/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx
@@ -127,6 +127,6 @@
     <value>Input object "{0}" is not numeric.</value>
   </data>
   <data name="AverageSwitchNotSet" xml:space="preserve">
-    <value>StdDeviation was requested and requires the average to be calculated, please add the -Average switch.</value>
+    <value>StdDeviation was requested and requires the average to be calculated, however '-Average' was set to $false.</value>
   </data>
 </root>

From f719ad9ab1c4eeb42745c9cd9e270f94778f60f5 Mon Sep 17 00:00:00 2001
From: CloudyDino <amaanmarfatia@gmail.com>
Date: Sat, 24 Feb 2018 18:01:29 -0500
Subject: [PATCH 06/19] Addressed comments by @iSazonov and @SteveL-MSFT

---
 .../commands/utility/Measure-Object.cs         | 18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index e99ad3e5a6e..de34bf7b206 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -293,8 +293,9 @@ public SwitchParameter StdDeviation
             set
             {
                 _measureStdDeviation = value;
-                if(value == true)
+                if (value) {
                     _measureAverage = true;
+                }
             }
         }
 
@@ -841,28 +842,17 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
                 if (_measureAverage && stat.count > 0)
                     average = stat.sum / stat.count;
 
-                if(_measureStdDeviation && !_measureAverage) {
-                    ErrorRecord errorRecord = new ErrorRecord(
-                        PSTraceSource.NewArgumentException("Average"),
-                        "AverageSwitchNotSet",
-                        ErrorCategory.InvalidArgument,
-                        null);
-
-                    errorRecord.ErrorDetails = new ErrorDetails(this, "MeasureObjectStrings", "AverageSwitchNotSet", "Average");
-                    WriteError(errorRecord);
-                }
-
                 if (_measureStdDeviation && _measureAverage && stat.count > 0)
                 {
                     var sumOfDerivation = 0.0;
 
                     foreach (double n in stat.stdDeviationNumbers)
                     {
-                        var m = n - (double)average;
+                        var m = n - average;
                         sumOfDerivation += m * m;
                     }
 
-                    stdDeviation = Math.Round(Math.Sqrt(sumOfDerivation / (stat.stdDeviationNumbers.Count - 1)), 4);
+                    stdDeviation = Math.Sqrt(sumOfDerivation / (stat.stdDeviationNumbers.Count - 1));
                 }
             }
 

From de861ab8d86344ba8659cfad6c923f84a5943fd3 Mon Sep 17 00:00:00 2001
From: CloudyDino <amaanmarfatia@gmail.com>
Date: Sat, 24 Feb 2018 19:24:37 -0500
Subject: [PATCH 07/19] Cast average outside for loop

---
 .../commands/utility/Measure-Object.cs                         | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index de34bf7b206..39945e7a835 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -846,9 +846,10 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
                 {
                     var sumOfDerivation = 0.0;
 
+                    var averageCasted = (double) average;
                     foreach (double n in stat.stdDeviationNumbers)
                     {
-                        var m = n - average;
+                        var m = n - averageCasted;
                         sumOfDerivation += m * m;
                     }
 

From 0f1c554689a993fd3e1b81154fc450cc99deb16c Mon Sep 17 00:00:00 2001
From: CloudyDino <amaanmarfatia@gmail.com>
Date: Sat, 24 Feb 2018 19:26:09 -0500
Subject: [PATCH 08/19] Updated Measure-Object.Tests.ps1 to match standard
 deviation calculations

---
 .../Measure-Object.Tests.ps1                          | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1 b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
index 6296f3466a9..fc7e934a354 100644
--- a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
+++ b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
@@ -19,13 +19,14 @@ Describe "Measure-Object" -Tags "CI" {
 
     It "Should calculate Standard Deviation" {
         $actual = ($testObject | Measure-Object -Average -StdDeviation)
-        $actual.StdDeviation | Should Be 1.5275
+        # We check this way since .StdDeviation returns a double value
+        [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
 
-    It "Should throw if Standard Deviation with -Average not specified" {
-        #{$testObject | Measure-Object -StdDeviation} | Should Throw
-        $actual = $testObject | Measure-Object -StdDeviation
-        $actual.StdDeviation | Should Be 1.5275
+    It "Should calculate Standard Deviation without -Average" {
+        $actual = ($testObject | Measure-Object -StdDeviation)
+        # We check this way since .StdDeviation returns a double value
+        [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
 
     It 'Should throw if Standard Deviation requested and -Average:$false' {

From e42c10e9170d9f43eaf85333601fcd3d7e756c85 Mon Sep 17 00:00:00 2001
From: Amaan Marfatia <amaanmarfatia@gmail.com>
Date: Sat, 10 Mar 2018 20:41:13 -0500
Subject: [PATCH 09/19] Change Standard Deviation calculation to be iterative

---
 .../commands/utility/Measure-Object.cs        | 40 ++++++++-----------
 1 file changed, 17 insertions(+), 23 deletions(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index 39945e7a835..9134f64620a 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -73,9 +73,7 @@ public GenericMeasureInfo()
         public double? Minimum { get; set; }
 
         /// <summary>
-        ///
         /// The Standard Deviation of property values
-        ///
         /// </summary>
         public double? StdDeviation { get; set; }
     }
@@ -137,9 +135,7 @@ public GenericObjectMeasureInfo()
         public object Minimum { get; set; }
 
         /// <summary>
-        ///
         /// The Standard Deviation of property values
-        ///
         /// </summary>
         public double? StdDeviation { get; set; }
     }
@@ -239,8 +235,8 @@ private class Statistics
 
             // Generic/Numeric statistics
             internal double sum = 0.0;
+            internal double sumPrevious = 0.0;
             internal double stdDeviation = 0.0;
-            internal List<double> stdDeviationNumbers = new List<double>();
             internal object max = null;
             internal object min = null;
 
@@ -293,9 +289,6 @@ public SwitchParameter StdDeviation
             set
             {
                 _measureStdDeviation = value;
-                if (value) {
-                    _measureAverage = true;
-                }
             }
         }
 
@@ -563,7 +556,7 @@ private void AnalyzeValue(string propertyName, object objValue)
                 AnalyzeString(strValue, stat);
             }
 
-            if (_measureAverage || _measureSum)
+            if (_measureAverage || _measureSum || _measureStdDeviation)
             {
                 double numValue = 0.0;
                 if (!LanguagePrimitives.TryConvertTo(objValue, out numValue))
@@ -746,10 +739,20 @@ private void AnalyzeString(string strValue, Statistics stat)
         /// </summary>
         private void AnalyzeNumber(double numValue, Statistics stat)
         {
-            if (_measureSum || _measureAverage)
+            if (_measureSum || _measureAverage || _measureStdDeviation)
+            {
+                stat.sumPrevious = stat.sum;
                 stat.sum += numValue;
+            }
             if (_measureStdDeviation)
-                stat.stdDeviationNumbers.Add(numValue);
+            {
+                double countMinusOne = stat.count - 1;
+                double avgPrevious = (countMinusOne == 0) ? 0 : (stat.sumPrevious / countMinusOne);
+                double avg = stat.sum / stat.count;
+                stat.stdDeviation *= countMinusOne;
+                stat.stdDeviation += (numValue - avgPrevious) * (numValue - avg);
+                stat.stdDeviation /= stat.count;
+            }
         }
 
         /// <summary>
@@ -842,18 +845,9 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
                 if (_measureAverage && stat.count > 0)
                     average = stat.sum / stat.count;
 
-                if (_measureStdDeviation && _measureAverage && stat.count > 0)
+                if (_measureStdDeviation)
                 {
-                    var sumOfDerivation = 0.0;
-
-                    var averageCasted = (double) average;
-                    foreach (double n in stat.stdDeviationNumbers)
-                    {
-                        var m = n - averageCasted;
-                        sumOfDerivation += m * m;
-                    }
-
-                    stdDeviation = Math.Sqrt(sumOfDerivation / (stat.stdDeviationNumbers.Count - 1));
+                    stdDeviation = stat.stdDeviation;
                 }
             }
 
@@ -944,7 +938,7 @@ private TextMeasureInfo CreateTextMeasureInfo(Statistics stat)
 
         /// <summary>
         /// Whether or not a numeric conversion error occurred.
-        /// If true, then average/sum will not be output.
+        /// If true, then average/sum/standard deviation will not be output.
         /// </summary>
         private bool _nonNumericError = false;
 

From 31c716332ff9d60ebf46702bb90f0682cad2bf66 Mon Sep 17 00:00:00 2001
From: Amaan Marfatia <amaanmarfatia@gmail.com>
Date: Sun, 11 Mar 2018 20:46:13 -0400
Subject: [PATCH 10/19] Remove unused error AverageSwitchNotSet

---
 .../resources/MeasureObjectStrings.resx                        | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx b/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx
index bccbd5db10c..8211114c335 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx
+++ b/src/Microsoft.PowerShell.Commands.Utility/resources/MeasureObjectStrings.resx
@@ -126,7 +126,4 @@
   <data name="NonNumericInputObject" xml:space="preserve">
     <value>Input object "{0}" is not numeric.</value>
   </data>
-  <data name="AverageSwitchNotSet" xml:space="preserve">
-    <value>StdDeviation was requested and requires the average to be calculated, however '-Average' was set to $false.</value>
-  </data>
 </root>

From b6c89dcd5680a09322e4861b4c196feb3ff202cd Mon Sep 17 00:00:00 2001
From: Amaan Marfatia <amaanmarfatia@gmail.com>
Date: Sun, 11 Mar 2018 23:23:42 -0400
Subject: [PATCH 11/19] Fixed calculation of standard deviation

---
 .../commands/utility/Measure-Object.cs             | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index 9134f64620a..2d5c2b91bd5 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -236,7 +236,7 @@ private class Statistics
             // Generic/Numeric statistics
             internal double sum = 0.0;
             internal double sumPrevious = 0.0;
-            internal double stdDeviation = 0.0;
+            internal double variance = 0.0;
             internal object max = null;
             internal object min = null;
 
@@ -744,14 +744,12 @@ private void AnalyzeNumber(double numValue, Statistics stat)
                 stat.sumPrevious = stat.sum;
                 stat.sum += numValue;
             }
-            if (_measureStdDeviation)
+            if (_measureStdDeviation && stat.count > 1)
             {
                 double countMinusOne = stat.count - 1;
-                double avgPrevious = (countMinusOne == 0) ? 0 : (stat.sumPrevious / countMinusOne);
-                double avg = stat.sum / stat.count;
-                stat.stdDeviation *= countMinusOne;
-                stat.stdDeviation += (numValue - avgPrevious) * (numValue - avg);
-                stat.stdDeviation /= stat.count;
+                double avgPrevious = stat.sumPrevious / countMinusOne;
+                stat.variance *= (countMinusOne - 1)/countMinusOne;
+                stat.variance += (numValue - avgPrevious) * (numValue - avgPrevious) / stat.count;
             }
         }
 
@@ -847,7 +845,7 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
 
                 if (_measureStdDeviation)
                 {
-                    stdDeviation = stat.stdDeviation;
+                    stdDeviation = Math.Sqrt(stat.variance);
                 }
             }
 

From 28114aafee01c0c35a8d5a3b6f35c73df62191bd Mon Sep 17 00:00:00 2001
From: Amaan Marfatia <amaanmarfatia@gmail.com>
Date: Sun, 11 Mar 2018 23:32:00 -0400
Subject: [PATCH 12/19] Added test for standard deviation

Asks to calculate the standard deviation for the integers [1, 100]
---
 .../Measure-Object.Tests.ps1                   | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1 b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
index fc7e934a354..d411a645093 100644
--- a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
+++ b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
@@ -3,6 +3,7 @@
 Describe "Measure-Object" -Tags "CI" {
     BeforeAll {
         $testObject = 1,3,4
+        $testObject2 = 1..100
     }
 
     It "Should be able to be called without error" {
@@ -23,22 +24,19 @@ Describe "Measure-Object" -Tags "CI" {
         [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
 
+
+    It "Should calculate Standard Deviation" {
+        $actual = ($testObject2 | Measure-Object -StdDeviation)
+        # We check this way since .StdDeviation returns a double value
+        [Math]::abs($actual.StdDeviation - 29.011491975882) | Should -BeLessThan .0000000000001
+    }
+
     It "Should calculate Standard Deviation without -Average" {
         $actual = ($testObject | Measure-Object -StdDeviation)
         # We check this way since .StdDeviation returns a double value
         [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
 
-    It 'Should throw if Standard Deviation requested and -Average:$false' {
-        try {
-            $Error.Clear()
-            $testObject | Measure-Object -StdDeviation -Average:$false -ErrorAction Stop
-        }
-        catch {
-            $Error.Count | should be 1
-        }
-    }
-
     It "Should be able to count using the Property switch" {
         $expected = $(Get-ChildItem $TestDrive).Length
         $actual   = $(Get-ChildItem $TestDrive | Measure-Object -Property Length).Count

From b6491e81ff9be78d4a56b4b1418470a07f58cd77 Mon Sep 17 00:00:00 2001
From: Amaan Marfatia <amaanmarfatia@gmail.com>
Date: Mon, 12 Mar 2018 14:50:05 -0400
Subject: [PATCH 13/19] Update standard deviation tests

Checks to make sure that -StdDeviation works with -Sum and -Average
---
 .../Measure-Object.Tests.ps1                  | 22 ++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1 b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
index d411a645093..d06b4957a9d 100644
--- a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
+++ b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
@@ -19,7 +19,7 @@ Describe "Measure-Object" -Tags "CI" {
     }
 
     It "Should calculate Standard Deviation" {
-        $actual = ($testObject | Measure-Object -Average -StdDeviation)
+        $actual = ($testObject | Measure-Object -StdDeviation)
         # We check this way since .StdDeviation returns a double value
         [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
@@ -31,12 +31,28 @@ Describe "Measure-Object" -Tags "CI" {
         [Math]::abs($actual.StdDeviation - 29.011491975882) | Should -BeLessThan .0000000000001
     }
 
-    It "Should calculate Standard Deviation without -Average" {
-        $actual = ($testObject | Measure-Object -StdDeviation)
+    It "Should calculate Standard Deviation with -Sum" {
+        $actual = ($testObject | Measure-Object -Sum -StdDeviation)
+        # We check this way since .StdDeviation returns a double value
+        $actual.Sum | Should Be 8
+        [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
+    }
+
+    It "Should calculate Standard Deviation with -Average" {
+        $actual = ($testObject | Measure-Object -Average -StdDeviation)
         # We check this way since .StdDeviation returns a double value
+        [Math]::abs($actual.Average - 2.66666666666667) | Should -BeLessThan .00000000000001
         [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
 
+    It "Should calculate Standard Deviation with -Sum -Average" {
+        $actual = ($testObject2 | Measure-Object -Sum -Average -StdDeviation)
+        # We check this way since .StdDeviation returns a double value
+        $actual.Sum | Should Be 5050
+        $actual.Average | Should Be 50.5
+        [Math]::abs($actual.StdDeviation - 29.011491975882) | Should -BeLessThan .0000000000001
+    }
+
     It "Should be able to count using the Property switch" {
         $expected = $(Get-ChildItem $TestDrive).Length
         $actual   = $(Get-ChildItem $TestDrive | Measure-Object -Property Length).Count

From c40ab47473e076bfec9de89829004fa2ed3f86ec Mon Sep 17 00:00:00 2001
From: Amaan Marfatia <amaanmarfatia@gmail.com>
Date: Mon, 12 Mar 2018 14:53:20 -0400
Subject: [PATCH 14/19] Update formatting and standard deviation calculation

Added periods to end of public comments and removed empty value tags as per iSazonov's request. Calculation of standard deviation is now cleaner.
---
 .../commands/utility/Measure-Object.cs           | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index 2d5c2b91bd5..57ac3a53db3 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -73,7 +73,7 @@ public GenericMeasureInfo()
         public double? Minimum { get; set; }
 
         /// <summary>
-        /// The Standard Deviation of property values
+        /// The Standard Deviation of property values.
         /// </summary>
         public double? StdDeviation { get; set; }
     }
@@ -135,7 +135,7 @@ public GenericObjectMeasureInfo()
         public object Minimum { get; set; }
 
         /// <summary>
-        /// The Standard Deviation of property values
+        /// The Standard Deviation of property values.
         /// </summary>
         public double? StdDeviation { get; set; }
     }
@@ -276,10 +276,9 @@ public MeasureObjectCommand()
         #endregion Common parameters in both sets
 
         /// <summary>
-        /// Set to true if Standard Deviation is to be returned
+        /// Set to true if Standard Deviation is to be returned.
         /// </summary>
-        /// <value></value>
-        [Parameter(ParameterSetName = GenericParameterSet)]
+            [Parameter(ParameterSetName = GenericParameterSet)]
         public SwitchParameter StdDeviation
         {
             get
@@ -746,9 +745,10 @@ private void AnalyzeNumber(double numValue, Statistics stat)
             }
             if (_measureStdDeviation && stat.count > 1)
             {
-                double countMinusOne = stat.count - 1;
-                double avgPrevious = stat.sumPrevious / countMinusOne;
-                stat.variance *= (countMinusOne - 1)/countMinusOne;
+                // Based off of iterative method of calculating variance on
+                // https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Online_algorithm
+                double avgPrevious = stat.sumPrevious / (stat.count - 1);
+                stat.variance *= (stat.count - 2.0) / (stat.count - 1);
                 stat.variance += (numValue - avgPrevious) * (numValue - avgPrevious) / stat.count;
             }
         }

From 1a9d6897e950d076fa6537449918dc56aead6afa Mon Sep 17 00:00:00 2001
From: Amaan Marfatia <amaanmarfatia@gmail.com>
Date: Wed, 14 Mar 2018 09:48:44 -0400
Subject: [PATCH 15/19] Mention how values for standard deviation tests were
 calculated

---
 .../Measure-Object.Tests.ps1                           | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1 b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
index d06b4957a9d..b6213178473 100644
--- a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
+++ b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
@@ -21,6 +21,8 @@ Describe "Measure-Object" -Tags "CI" {
     It "Should calculate Standard Deviation" {
         $actual = ($testObject | Measure-Object -StdDeviation)
         # We check this way since .StdDeviation returns a double value
+        # 1.52752523165195 was calculated outside powershell using formula from
+        # http://mathworld.wolfram.com/StandardDeviation.html
         [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
 
@@ -28,6 +30,8 @@ Describe "Measure-Object" -Tags "CI" {
     It "Should calculate Standard Deviation" {
         $actual = ($testObject2 | Measure-Object -StdDeviation)
         # We check this way since .StdDeviation returns a double value
+        # 29.011491975882 was calculated outside powershell using formula from
+        # http://mathworld.wolfram.com/StandardDeviation.html
         [Math]::abs($actual.StdDeviation - 29.011491975882) | Should -BeLessThan .0000000000001
     }
 
@@ -35,6 +39,8 @@ Describe "Measure-Object" -Tags "CI" {
         $actual = ($testObject | Measure-Object -Sum -StdDeviation)
         # We check this way since .StdDeviation returns a double value
         $actual.Sum | Should Be 8
+        # 1.52752523165195 was calculated outside powershell using formula from
+        # http://mathworld.wolfram.com/StandardDeviation.html
         [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
 
@@ -42,6 +48,8 @@ Describe "Measure-Object" -Tags "CI" {
         $actual = ($testObject | Measure-Object -Average -StdDeviation)
         # We check this way since .StdDeviation returns a double value
         [Math]::abs($actual.Average - 2.66666666666667) | Should -BeLessThan .00000000000001
+        # 1.52752523165195 was calculated outside powershell using formula from
+        # http://mathworld.wolfram.com/StandardDeviation.html
         [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
 
@@ -50,6 +58,8 @@ Describe "Measure-Object" -Tags "CI" {
         # We check this way since .StdDeviation returns a double value
         $actual.Sum | Should Be 5050
         $actual.Average | Should Be 50.5
+        # 29.011491975882 was calculated outside powershell using formula from
+        # http://mathworld.wolfram.com/StandardDeviation.html
         [Math]::abs($actual.StdDeviation - 29.011491975882) | Should -BeLessThan .0000000000001
     }
 

From 1820a410507989e482f03649b5fd65b273f333d1 Mon Sep 17 00:00:00 2001
From: Amaan Marfatia <amaanmarfatia@gmail.com>
Date: Wed, 14 Mar 2018 09:49:10 -0400
Subject: [PATCH 16/19] Remove standard deviation from GenericMeasureInfo

---
 .../commands/utility/Measure-Object.cs                           | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index 57ac3a53db3..89917c90f36 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -883,7 +883,6 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
                 gmi.Count = stat.count;
                 gmi.Sum = sum;
                 gmi.Average = average;
-                gmi.StdDeviation = stdDeviation;
                 if (null != max)
                 {
                     gmi.Maximum = (double)max;

From 23bd24b1fca4f75368db203f7b90077c6ef5e64f Mon Sep 17 00:00:00 2001
From: Amaan Marfatia <amaanmarfatia@gmail.com>
Date: Wed, 14 Mar 2018 13:32:32 -0400
Subject: [PATCH 17/19] Unindent line

---
 .../commands/utility/Measure-Object.cs                          | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index 89917c90f36..912606c78e0 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -278,7 +278,7 @@ public MeasureObjectCommand()
         /// <summary>
         /// Set to true if Standard Deviation is to be returned.
         /// </summary>
-            [Parameter(ParameterSetName = GenericParameterSet)]
+        [Parameter(ParameterSetName = GenericParameterSet)]
         public SwitchParameter StdDeviation
         {
             get

From df8ac60092a752f60c516e1d20a3fd4e7c4b806e Mon Sep 17 00:00:00 2001
From: Amaan Marfatia <amaanmarfatia@gmail.com>
Date: Wed, 14 Mar 2018 14:14:55 -0400
Subject: [PATCH 18/19] revert commit 1820a41

Standard Devation wasn't being displayed after commit 1820a410507989e482f03649b5fd65b273f333d1
---
 .../commands/utility/Measure-Object.cs                           | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index 912606c78e0..63501feb9b2 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -883,6 +883,7 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
                 gmi.Count = stat.count;
                 gmi.Sum = sum;
                 gmi.Average = average;
+                gmi.StdDeviation = stdDeviation;
                 if (null != max)
                 {
                     gmi.Maximum = (double)max;

From ea6fe0f6e638cbe0a7f825745dcfdf5abac88928 Mon Sep 17 00:00:00 2001
From: Amaan Marfatia <amaanmarfatia@gmail.com>
Date: Wed, 14 Mar 2018 21:32:56 -0400
Subject: [PATCH 19/19] Change StdDeviation to StandardDeviation to be
 consistent

---
 .../commands/utility/Measure-Object.cs        | 30 +++++++++----------
 .../Measure-Object.Tests.ps1                  | 30 +++++++++----------
 2 files changed, 30 insertions(+), 30 deletions(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
index 63501feb9b2..62bebc4d212 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/Measure-Object.cs
@@ -34,7 +34,7 @@ public sealed class GenericMeasureInfo : MeasureInfo
         /// </summary>
         public GenericMeasureInfo()
         {
-            Average = Sum = Maximum = Minimum = StdDeviation = null;
+            Average = Sum = Maximum = Minimum = StandardDeviation = null;
         }
 
         /// <summary>
@@ -75,7 +75,7 @@ public GenericMeasureInfo()
         /// <summary>
         /// The Standard Deviation of property values.
         /// </summary>
-        public double? StdDeviation { get; set; }
+        public double? StandardDeviation { get; set; }
     }
 
     /// <summary>
@@ -95,7 +95,7 @@ public sealed class GenericObjectMeasureInfo : MeasureInfo
         /// </summary>
         public GenericObjectMeasureInfo()
         {
-            Average = Sum = StdDeviation = null;
+            Average = Sum = StandardDeviation = null;
             Maximum = Minimum = null;
         }
 
@@ -137,7 +137,7 @@ public GenericObjectMeasureInfo()
         /// <summary>
         /// The Standard Deviation of property values.
         /// </summary>
-        public double? StdDeviation { get; set; }
+        public double? StandardDeviation { get; set; }
     }
 
     /// <summary>
@@ -279,19 +279,19 @@ public MeasureObjectCommand()
         /// Set to true if Standard Deviation is to be returned.
         /// </summary>
         [Parameter(ParameterSetName = GenericParameterSet)]
-        public SwitchParameter StdDeviation
+        public SwitchParameter StandardDeviation
         {
             get
             {
-                return _measureStdDeviation;
+                return _measureStandardDeviation;
             }
             set
             {
-                _measureStdDeviation = value;
+                _measureStandardDeviation = value;
             }
         }
 
-        private bool _measureStdDeviation;
+        private bool _measureStandardDeviation;
 
         /// <summary>
         /// Set to true is Sum is to be returned
@@ -555,7 +555,7 @@ private void AnalyzeValue(string propertyName, object objValue)
                 AnalyzeString(strValue, stat);
             }
 
-            if (_measureAverage || _measureSum || _measureStdDeviation)
+            if (_measureAverage || _measureSum || _measureStandardDeviation)
             {
                 double numValue = 0.0;
                 if (!LanguagePrimitives.TryConvertTo(objValue, out numValue))
@@ -738,12 +738,12 @@ private void AnalyzeString(string strValue, Statistics stat)
         /// </summary>
         private void AnalyzeNumber(double numValue, Statistics stat)
         {
-            if (_measureSum || _measureAverage || _measureStdDeviation)
+            if (_measureSum || _measureAverage || _measureStandardDeviation)
             {
                 stat.sumPrevious = stat.sum;
                 stat.sum += numValue;
             }
-            if (_measureStdDeviation && stat.count > 1)
+            if (_measureStandardDeviation && stat.count > 1)
             {
                 // Based off of iterative method of calculating variance on
                 // https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Online_algorithm
@@ -831,7 +831,7 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
         {
             double? sum = null;
             double? average = null;
-            double? stdDeviation = null;
+            double? StandardDeviation = null;
             object max = null;
             object min = null;
 
@@ -843,9 +843,9 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
                 if (_measureAverage && stat.count > 0)
                     average = stat.sum / stat.count;
 
-                if (_measureStdDeviation)
+                if (_measureStandardDeviation)
                 {
-                    stdDeviation = Math.Sqrt(stat.variance);
+                    StandardDeviation = Math.Sqrt(stat.variance);
                 }
             }
 
@@ -883,7 +883,7 @@ private MeasureInfo CreateGenericMeasureInfo(Statistics stat, bool shouldUseGene
                 gmi.Count = stat.count;
                 gmi.Sum = sum;
                 gmi.Average = average;
-                gmi.StdDeviation = stdDeviation;
+                gmi.StandardDeviation = StandardDeviation;
                 if (null != max)
                 {
                     gmi.Maximum = (double)max;
diff --git a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1 b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
index b6213178473..0a5b4af2a93 100644
--- a/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
+++ b/test/powershell/Modules/Microsoft.PowerShell.Utility/Measure-Object.Tests.ps1
@@ -19,48 +19,48 @@ Describe "Measure-Object" -Tags "CI" {
     }
 
     It "Should calculate Standard Deviation" {
-        $actual = ($testObject | Measure-Object -StdDeviation)
-        # We check this way since .StdDeviation returns a double value
+        $actual = ($testObject | Measure-Object -StandardDeviation)
+        # We check this way since .StandardDeviation returns a double value
         # 1.52752523165195 was calculated outside powershell using formula from
         # http://mathworld.wolfram.com/StandardDeviation.html
-        [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
+        [Math]::abs($actual.StandardDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
 
 
     It "Should calculate Standard Deviation" {
-        $actual = ($testObject2 | Measure-Object -StdDeviation)
-        # We check this way since .StdDeviation returns a double value
+        $actual = ($testObject2 | Measure-Object -StandardDeviation)
+        # We check this way since .StandardDeviation returns a double value
         # 29.011491975882 was calculated outside powershell using formula from
         # http://mathworld.wolfram.com/StandardDeviation.html
-        [Math]::abs($actual.StdDeviation - 29.011491975882) | Should -BeLessThan .0000000000001
+        [Math]::abs($actual.StandardDeviation - 29.011491975882) | Should -BeLessThan .0000000000001
     }
 
     It "Should calculate Standard Deviation with -Sum" {
-        $actual = ($testObject | Measure-Object -Sum -StdDeviation)
-        # We check this way since .StdDeviation returns a double value
+        $actual = ($testObject | Measure-Object -Sum -StandardDeviation)
+        # We check this way since .StandardDeviation returns a double value
         $actual.Sum | Should Be 8
         # 1.52752523165195 was calculated outside powershell using formula from
         # http://mathworld.wolfram.com/StandardDeviation.html
-        [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
+        [Math]::abs($actual.StandardDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
 
     It "Should calculate Standard Deviation with -Average" {
-        $actual = ($testObject | Measure-Object -Average -StdDeviation)
-        # We check this way since .StdDeviation returns a double value
+        $actual = ($testObject | Measure-Object -Average -StandardDeviation)
+        # We check this way since .StandardDeviation returns a double value
         [Math]::abs($actual.Average - 2.66666666666667) | Should -BeLessThan .00000000000001
         # 1.52752523165195 was calculated outside powershell using formula from
         # http://mathworld.wolfram.com/StandardDeviation.html
-        [Math]::abs($actual.StdDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
+        [Math]::abs($actual.StandardDeviation - 1.52752523165195) | Should -BeLessThan .00000000000001
     }
 
     It "Should calculate Standard Deviation with -Sum -Average" {
-        $actual = ($testObject2 | Measure-Object -Sum -Average -StdDeviation)
-        # We check this way since .StdDeviation returns a double value
+        $actual = ($testObject2 | Measure-Object -Sum -Average -StandardDeviation)
+        # We check this way since .StandardDeviation returns a double value
         $actual.Sum | Should Be 5050
         $actual.Average | Should Be 50.5
         # 29.011491975882 was calculated outside powershell using formula from
         # http://mathworld.wolfram.com/StandardDeviation.html
-        [Math]::abs($actual.StdDeviation - 29.011491975882) | Should -BeLessThan .0000000000001
+        [Math]::abs($actual.StandardDeviation - 29.011491975882) | Should -BeLessThan .0000000000001
     }
 
     It "Should be able to count using the Property switch" {