From 3fe639e491416eb1cd8299899b9911c3e1abc883 Mon Sep 17 00:00:00 2001
From: Miha Kralj <miha.kralj@outlook.com>
Date: Tue, 15 Nov 2022 22:02:02 -0800
Subject: [PATCH] COVAR

semver fix
---
 GitVersion.yml                     |  1 -
 Source/Statistics/COVAR_Series.cs  | 67 ++++++++++++++++++++++++++++++
 Tests/Validations/Skender_Stock.cs |  9 ++++
 docs/readme.md                     |  2 +-
 4 files changed, 77 insertions(+), 2 deletions(-)
 create mode 100644 Source/Statistics/COVAR_Series.cs

diff --git a/GitVersion.yml b/GitVersion.yml
index deb60508..a2c78995 100644
--- a/GitVersion.yml
+++ b/GitVersion.yml
@@ -1,4 +1,3 @@
-next-version: 0.1.19
 minor-version-bump-message: \+semver:\s?(feature|new)
 branches:
   main:
diff --git a/Source/Statistics/COVAR_Series.cs b/Source/Statistics/COVAR_Series.cs
new file mode 100644
index 00000000..06c3463d
--- /dev/null
+++ b/Source/Statistics/COVAR_Series.cs
@@ -0,0 +1,67 @@
+namespace QuanTAlib;
+using System;
+
+/* <summary>
+COVAR: Covariance
+   Covariance is defined as the expected value (or mean) of the product
+   of their deviations from their individual expected values.
+
+Sources:
+  https://en.wikipedia.org/wiki/Covariance
+
+</summary> */
+
+public class COVAR_Series : Pair_TSeries_Indicator
+{
+  public COVAR_Series(TSeries d1, TSeries d2, int period, bool useNaN = false) : base(d1, d2, period, useNaN)
+  {
+    if (base._d1.Count > 0 && base._d2.Count > 0) { for (int i = 0; i < base._d1.Count; i++) { this.Add(base._d1[i], base._d2[i], false); } }
+  }
+
+  private readonly System.Collections.Generic.List<double> _x = new();
+  private readonly System.Collections.Generic.List<double> _xx = new();
+  private readonly System.Collections.Generic.List<double> _y = new();
+  private readonly System.Collections.Generic.List<double> _yy = new();
+  private readonly System.Collections.Generic.List<double> _xy = new();
+
+  public override void Add((System.DateTime t, double v) TValue1, (System.DateTime t, double v) TValue2, bool update)
+  {
+    if (update)
+    {
+      _x[_x.Count - 1] = TValue1.v;
+      _xx[_xx.Count - 1] = TValue1.v * TValue1.v;
+      _y[_y.Count - 1] = TValue2.v;
+      _y[_yy.Count - 1] = TValue2.v * TValue2.v;
+      _xy[_xy.Count - 1] = TValue1.v * TValue2.v;
+    }
+    else
+    {
+      _x.Add(TValue1.v);
+      _xx.Add(TValue1.v * TValue1.v);
+      _y.Add(TValue2.v);
+      _yy.Add(TValue2.v * TValue2.v);
+      _xy.Add(TValue1.v * TValue2.v);
+    }
+    if (_x.Count > this._p) { _x.RemoveAt(0); }
+    if (_xx.Count > this._p) { _xx.RemoveAt(0); }
+    if (_y.Count > this._p) { _y.RemoveAt(0); }
+    if (_yy.Count > this._p) { _yy.RemoveAt(0); }
+    if (_xy.Count > this._p) { _xy.RemoveAt(0); }
+
+    double _sumx = 0;
+    for (int i = 0; i < _x.Count; i++) { _sumx += _x[i]; }
+    double _sumxx = 0;
+    for (int i = 0; i < _xx.Count; i++) { _sumxx += _xx[i]; }
+    double _sumy = 0;
+    for (int i = 0; i < _y.Count; i++) { _sumy += _y[i]; }
+    double _sumyy = 0;
+    for (int i = 0; i < _yy.Count; i++) { _sumyy += _yy[i]; }
+    double _sumxy = 0;
+    for (int i = 0; i < _xy.Count; i++) { _sumxy += _xy[i]; }
+
+    double _covar = (_sumxy / _p) - ((_sumx / _p) * (_sumy / _p));
+
+    var result = (TValue1.t, (this.Count < this._p - 1 && this._NaN) ? double.NaN : _covar);
+    if (update) { base[base.Count - 1] = result; } else { base.Add(result); }
+  }
+}
\ No newline at end of file
diff --git a/Tests/Validations/Skender_Stock.cs b/Tests/Validations/Skender_Stock.cs
index c2976b00..fcc27368 100644
--- a/Tests/Validations/Skender_Stock.cs
+++ b/Tests/Validations/Skender_Stock.cs
@@ -98,6 +98,15 @@ public class Skender_Stock
     Assert.Equal(Math.Round((double)SK.Last().Mape!, 6), Math.Round(QL.Last().v, 6));
   }
 
+  [Fact]
+  public void COVAR()
+  {
+    COVAR_Series QL = new(bars.High, bars.Low, period, false);
+    var SK = quotes.Use(CandlePart.High).GetCorrelation(quotes.Use(CandlePart.Low), period);
+
+    Assert.Equal(Math.Round((double)SK.Last().Covariance!, 6), Math.Round(QL.Last().v, 6));
+  }
+
   [Fact]
   public void CORR()
   {
diff --git a/docs/readme.md b/docs/readme.md
index eff2c21c..53c77b6c 100644
--- a/docs/readme.md
+++ b/docs/readme.md
@@ -56,7 +56,7 @@ See [Getting Started](https://github.com/mihakralj/QuanTAlib/blob/main/Docs/gett
 | **STATISTICS & NUMERICAL ANALYSIS** | **QuanTAlib** | **TA-LIB** | **Skender** | **Pandas TA** |
 | ⭐ BIAS - Bias | `BIAS_Series` ||| bias |
 | ⭐ CORR - Pearson's Correlation Coefficient | `CORR_Series` | CORREL | GetCorrelation ||
-| ⛔ COVAR - Covariance ||| GetCorrelation ||
+| ⭐ COVAR - Covariance | `COVAR_Series` || GetCorrelation ||
 | ⭐ ENTP - Entropy | `ENTP_Series` ||| entropy |
 | ⭐ KURT - Kurtosis | `KURT_Series` ||| kurtosis |
 | ⭐ LINREG - Linear Regression | `LINREG_Series` || GetSlope ||