feature: add Sortino ratio

pkg/types/sharpe.go

@@ -7,20 +7,14 @@ import (
 // Sharpe: Calcluates the sharpe ratio of access returns
 //
 // @param returns (Series): Series of profit/loss percentage every specific interval
-// @param periods (int): Freq. of returns (252/365 for daily, 12 for monthy)
+// @param periods (int): Freq. of returns (252/365 for daily, 12 for monthy, 1 for annually)
 // @param annualize (bool): return annualize sharpe?
 // @param smart (bool): return smart sharpe ratio
 func Sharpe(returns Series, periods int, annualize bool, smart bool) float64 {
 	data := returns
-	num := data.Length()
-	divisor := Stdev(data, data.Length(), 1)
+	var divisor = Stdev(data, data.Length(), 1)
 	if smart {
-		sum := 0.
-		coef := math.Abs(Correlation(data, Shift(data, 1), num-1))
-		for i := 1; i < num; i++ {
-			sum += float64(num-i) / float64(num) * math.Pow(coef, float64(i))
-		}
-		divisor = divisor * math.Sqrt(1.+2.*sum)
+		divisor *= autocorrPenalty(returns)
 	}
 	result := Mean(data) / divisor
 	if annualize {
@@ -28,3 +22,17 @@ func Sharpe(returns Series, periods int, annualize bool, smart bool) float64 {
 	}
 	return result
 }
+
+func avgReturnRate(returnRate float64, periods int) float64 {
+	return math.Pow(1.+returnRate, 1./float64(periods)) - 1.
+}
+
+func autocorrPenalty(data Series) float64 {
+	num := data.Length()
+	coef := math.Abs(Correlation(data, Shift(data, 1), num-1))
+	var sum = 0.
+	for i := 1; i < num; i++ {
+		sum += float64(num-i) / float64(num) * math.Pow(coef, float64(i))
+	}
+	return math.Sqrt(1. + 2.*sum)
+}

pkg/types/sortino.go

@@ -0,0 +1,44 @@
+package types
+
+import (
+	"math"
+)
+
+// Sortino: Calcluates the sotino ratio of access returns
+//
+//           ROI_excess   E[ROI] - ROI_risk_free
+// sortino = ---------- = -----------------------
+//              risk      sqrt(E[ROI_drawdown^2])
+//
+// @param returns (Series): Series of profit/loss percentage every specific interval
+// @param riskFreeReturns (float): risk-free return rate of year
+// @param periods (int): Freq. of returns (252/365 for daily, 12 for monthy, 1 for annually)
+// @param annualize (bool): return annualize sortino?
+// @param smart (bool): return smart sharpe ratio
+func Sortino(returns Series, riskFreeReturns float64, periods int, annualize bool, smart bool) float64 {
+	avgRiskFreeReturns := 0.
+	excessReturn := Mean(returns)
+	if riskFreeReturns > 0. && periods > 0 {
+		avgRiskFreeReturns = avgReturnRate(riskFreeReturns, periods)
+		excessReturn -= avgRiskFreeReturns
+	}
+
+	num := returns.Length()
+	var sum = 0.
+	for i := 0; i < num; i++ {
+		exRet := returns.Index(i) - avgRiskFreeReturns
+		if exRet < 0 {
+			sum += exRet * exRet
+		}
+	}
+	var risk = math.Sqrt(sum / float64(num))
+	if smart {
+		risk *= autocorrPenalty(returns)
+	}
+
+	result := excessReturn / risk
+	if annualize {
+		return result * math.Sqrt(float64(periods))
+	}
+	return result
+}

pkg/types/sortino_test.go

@@ -0,0 +1,26 @@
+package types
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+/*
+python
+
+import quantstats as qx
+import pandas as pd
+
+print(qx.stats.sortino(pd.Series([0.01, -0.03, 0.1, -0.02, 0.001]), 0.00, 0, False, False))
+print(qx.stats.sortino(pd.Series([0.01, -0.03, 0.1, -0.02, 0.001]), 0.03, 252, False, False))
+print(qx.stats.sortino(pd.Series([0.01, -0.03, 0.1, -0.02, 0.001]), 0.03, 252, True, False))
+*/
+func TestSortino(t *testing.T) {
+	var a Series = &Float64Slice{0.01, -0.03, 0.1, -0.02, 0.001}
+	output := Sortino(a, 0.03, 0, false, false)
+	assert.InDelta(t, output, 0.75661, 0.0001)
+	output = Sortino(a, 0.03, 252, false, false)
+	assert.InDelta(t, output, 0.74597, 0.0001)
+	output = Sortino(a, 0.03, 252, true, false)
+	assert.InDelta(t, output, 11.84192, 0.0001)
+}

pkg/types/trade_stats.go

@@ -125,6 +125,18 @@ func (s *IntervalProfitCollector) GetSharpe() float64 {
 	return Sharpe(Minus(s.Profits, 1.), s.Profits.Length(), true, false)
 }
 
+// Get sortino value with the interval of profit collected.
+// No risk-free return rate and smart sortino OFF for the calculated result.
+func (s *IntervalProfitCollector) GetSortino() float64 {
+	if s.tmpTime.IsZero() {
+		panic("No valid start time. Did you create IntervalProfitCollector instance using NewIntervalProfitCollector?")
+	}
+	if s.Profits == nil {
+		panic("profits array empty. Did you create IntervalProfitCollector instance using NewIntervalProfitCollector?")
+	}
+	return Sortino(Minus(s.Profits, 1.), 0., s.Profits.Length(), true, false)
+}
+
 func (s *IntervalProfitCollector) GetOmega() float64 {
 	return Omega(Minus(s.Profits, 1.))
 }
@@ -132,6 +144,7 @@ func (s *IntervalProfitCollector) GetOmega() float64 {
 func (s IntervalProfitCollector) MarshalYAML() (interface{}, error) {
 	result := make(map[string]interface{})
 	result["Sharpe Ratio"] = s.GetSharpe()
+	result["Sortino Ratio"] = s.GetSortino()
 	result["Omega Ratio"] = s.GetOmega()
 	result["Profitable Count"] = s.GetNumOfProfitableIntervals()
 	result["NonProfitable Count"] = s.GetNumOfNonProfitableIntervals()