Add WithValueFunc to Series to fix bug with accessing Value()

data.go

@@ -18,14 +18,6 @@ import (
 	"golang.org/x/exp/slices"
 )
 
-// EasyIndex returns an index to the `n` -length object that allows for negative indexing. For example, EasyIndex(-1, 5) returns 4. This is similar to Python's negative indexing. The return value may be less than zero if (-i) > n.
-func EasyIndex(i, n int) int {
-	if i < 0 {
-		return n + i
-	}
-	return i
-}
-
 type Series interface {
 	Signaler
 
@@ -47,6 +39,9 @@ type Series interface {
 
 	// Statistical functions.
 	Rolling(period int) *RollingSeries
+
+	// WithValueFunc is used to implement other types of Series that may modify the values by applying a function before returning them, for example. This returns a Series that is a copy of the original with the new value function used whenever a value is requested outside of the Value() method, which will still return the original value.
+	WithValueFunc(value func(i int) interface{}) Series
 }
 
 type Frame interface {
@@ -95,11 +90,14 @@ func (s *AppliedSeries) Value(i int) interface{} {
 	return s.apply(EasyIndex(i, s.Len()), s.Series.Value(i))
 }
 
+func (s *AppliedSeries) WithValueFunc(value func(i int) interface{}) Series {
+	return &AppliedSeries{Series: s.Series.WithValueFunc(value), apply: s.apply}
+}
+
 func NewAppliedSeries(s Series, apply func(i int, val interface{}) interface{}) *AppliedSeries {
-	return &AppliedSeries{
+	appliedSeries := &AppliedSeries{apply: apply}
-		Series: s,
+	appliedSeries.Series = s.WithValueFunc(appliedSeries.Value)
-		apply:  apply,
+	return appliedSeries
-	}
 }
 
 type RollingSeries struct {
@@ -107,146 +105,139 @@ type RollingSeries struct {
 	period int
 }
 
+// Average is an alias for Mean.
+func (s *RollingSeries) Average() *AppliedSeries {
+	return s.Mean()
+}
+
 func (s *RollingSeries) Mean() *AppliedSeries {
-	return &AppliedSeries{
+	return NewAppliedSeries(s, func(_ int, v interface{}) interface{} {
-		Series: s,
+		switch v := v.(type) {
-		apply: func(_ int, v interface{}) interface{} {
+		case []interface{}:
-			switch v := v.(type) {
+			if len(v) == 0 {
-			case []interface{}:
+				return nil
-				if len(v) == 0 {
-					return nil
-				}
-				switch v[0].(type) {
-				case float64:
-					var sum float64
-					for _, v := range v {
-						sum += v.(float64)
-					}
-					return sum / float64(len(v))
-				case int64:
-					var sum int64
-					for _, v := range v {
-						sum += v.(int64)
-					}
-					return sum / int64(len(v))
-				default:
-					return v[len(v)-1] // Do nothing
-				}
-			default:
-				panic(fmt.Sprintf("expected a slice of values, got %t", v))
 			}
-		},
+			switch v[0].(type) {
-	}
+			case float64:
+				var sum float64
+				for _, v := range v {
+					sum += v.(float64)
+				}
+				return sum / float64(len(v))
+			case int64:
+				var sum int64
+				for _, v := range v {
+					sum += v.(int64)
+				}
+				return sum / int64(len(v))
+			default:
+				return v[len(v)-1] // Do nothing
+			}
+		default:
+			panic(fmt.Sprintf("expected a slice of values, got %t", v))
+		}
+	})
 }
 
 func (s *RollingSeries) EMA() *AppliedSeries {
-	return &AppliedSeries{
+	return NewAppliedSeries(s, func(i int, v interface{}) interface{} {
-		Series: s,
+		switch v := v.(type) {
-		apply: func(i int, v interface{}) interface{} {
+		case []interface{}:
-			switch v := v.(type) {
+			if len(v) == 0 {
-			case []interface{}:
+				return nil
-				if len(v) == 0 {
-					return nil
-				}
-				switch v[0].(type) {
-				case float64:
-					ema := v[0].(float64)
-					for _, v := range v[1:] {
-						ema += (v.(float64) - ema) * 2 / (float64(s.period) + 1)
-					}
-					return ema
-				case int64:
-					ema := v[0].(int64)
-					for _, v := range v[1:] {
-						ema += (v.(int64) - ema) * 2 / (int64(s.period) + 1)
-					}
-					return ema
-				default: // string, time.Time
-					return v[len(v)-1] // Do nothing
-				}
-			default:
-				panic(fmt.Sprintf("expected a slice of values, got %t", v))
 			}
-		},
+			switch v[0].(type) {
-	}
+			case float64:
+				ema := v[0].(float64)
+				for _, v := range v[1:] {
+					ema += (v.(float64) - ema) * 2 / (float64(s.period) + 1)
+				}
+				return ema
+			case int64:
+				ema := v[0].(int64)
+				for _, v := range v[1:] {
+					ema += (v.(int64) - ema) * 2 / (int64(s.period) + 1)
+				}
+				return ema
+			default: // string, time.Time
+				return v[len(v)-1] // Do nothing
+			}
+		default:
+			panic(fmt.Sprintf("expected a slice of values, got %t", v))
+		}
+	})
 }
 
 func (s *RollingSeries) Median() *AppliedSeries {
-	return &AppliedSeries{
+	return NewAppliedSeries(s, func(_ int, v interface{}) interface{} {
-		Series: s,
+		switch v := v.(type) {
-		apply: func(_ int, v interface{}) interface{} {
+		case []interface{}:
-			switch v := v.(type) {
+			if len(v) == 0 {
-			case []interface{}:
+				return nil
-				if len(v) == 0 {
-					return nil
-				}
-				switch v[0].(type) {
-				case float64:
-					if len(v) == 0 {
-						return float64(0)
-					}
-					slices.SortFunc(v, func(a, b interface{}) bool {
-						x, y := a.(float64), b.(float64)
-						return x < y || (math.IsNaN(x) && !math.IsNaN(y))
-					})
-					if len(v)%2 == 0 {
-						return (v[len(v)/2-1].(float64) + v[len(v)/2].(float64)) / 2
-					}
-					return v[len(v)/2]
-				case int64:
-					if len(v) == 0 {
-						return int64(0)
-					}
-					slices.SortFunc(v, func(a, b interface{}) bool {
-						x, y := a.(int64), b.(int64)
-						return x < y
-					})
-					if len(v)%2 == 0 {
-						return (v[len(v)/2-1].(int64) + v[len(v)/2].(int64)) / 2
-					}
-					return v[len(v)/2]
-				default: // string, time.Time
-					return v[len(v)-1] // Do nothing
-				}
-			default:
-				panic(fmt.Sprintf("expected a slice of values, got %t", v))
 			}
-		},
+			switch v[0].(type) {
-	}
+			case float64:
+				if len(v) == 0 {
+					return float64(0)
+				}
+				slices.SortFunc(v, func(a, b interface{}) bool {
+					x, y := a.(float64), b.(float64)
+					return x < y || (math.IsNaN(x) && !math.IsNaN(y))
+				})
+				if len(v)%2 == 0 {
+					return (v[len(v)/2-1].(float64) + v[len(v)/2].(float64)) / 2
+				}
+				return v[len(v)/2]
+			case int64:
+				if len(v) == 0 {
+					return int64(0)
+				}
+				slices.SortFunc(v, func(a, b interface{}) bool {
+					x, y := a.(int64), b.(int64)
+					return x < y
+				})
+				if len(v)%2 == 0 {
+					return (v[len(v)/2-1].(int64) + v[len(v)/2].(int64)) / 2
+				}
+				return v[len(v)/2]
+			default: // string, time.Time
+				return v[len(v)-1] // Do nothing
+			}
+		default:
+			panic(fmt.Sprintf("expected a slice of values, got %t", v))
+		}
+	})
 }
 
 func (s *RollingSeries) StdDev() *AppliedSeries {
-	return &AppliedSeries{
+	return NewAppliedSeries(s, func(i int, v interface{}) interface{} {
-		Series: s,
+		switch v := v.(type) {
-		apply: func(i int, v interface{}) interface{} {
+		case []interface{}:
-			switch v := v.(type) {
+			if len(v) == 0 {
-			case []interface{}:
+				return nil
-				if len(v) == 0 {
-					return nil
-				}
-				switch v[0].(type) {
-				case float64:
-					mean := s.Mean().Value(i).(float64) // Take the mean of the last period values for the current index
-					var sum float64
-					for _, v := range v {
-						sum += (v.(float64) - mean) * (v.(float64) - mean)
-					}
-					return math.Sqrt(sum / float64(len(v)))
-				case int64:
-					mean := s.Mean().Value(i).(int64)
-					var sum int64
-					for _, v := range v {
-						sum += (v.(int64) - mean) * (v.(int64) - mean)
-					}
-					return int64(math.Sqrt(float64(sum) / float64(len(v))))
-				default: // A slice of something else, just return the last value
-					return v[len(v)-1] // Do nothing
-				}
-			default:
-				panic(fmt.Sprintf("expected a slice of values, got %t", v))
 			}
-		},
+			switch v[0].(type) {
-	}
+			case float64:
+				mean := s.Mean().Value(i).(float64) // Take the mean of the last period values for the current index
+				var sum float64
+				for _, v := range v {
+					sum += (v.(float64) - mean) * (v.(float64) - mean)
+				}
+				return math.Sqrt(sum / float64(len(v)))
+			case int64:
+				mean := s.Mean().Value(i).(int64)
+				var sum int64
+				for _, v := range v {
+					sum += (v.(int64) - mean) * (v.(int64) - mean)
+				}
+				return int64(math.Sqrt(float64(sum) / float64(len(v))))
+			default: // A slice of something else, just return the last value
+				return v[len(v)-1] // Do nothing
+			}
+		default:
+			panic(fmt.Sprintf("expected a slice of values, got %t", v))
+		}
+	})
 }
 
 // Value returns []interface{} up to `period` long. The last item in the slice is the item at i. If i is out of bounds, nil is returned.
@@ -263,6 +254,10 @@ func (s *RollingSeries) Value(i int) interface{} {
 	return items
 }
 
+func (s *RollingSeries) WithValueFunc(value func(i int) interface{}) Series {
+	return &RollingSeries{Series: s.Series.WithValueFunc(value), period: s.period}
+}
+
 // DataSeries is a Series that wraps a column of data. The data can be of the following types: float64, int64, string, or time.Time.
 //
 // Signals:
@@ -270,7 +265,8 @@ func (s *RollingSeries) Value(i int) interface{} {
 //   - NameChanged(string) - when the name is changed.
 type DataSeries struct {
 	SignalManager
-	data df.Series
+	data  df.Series
+	value func(i int) interface{}
 }
 
 // Copy copies the Series from start to end (inclusive). If end is -1, it will copy to the end of the Series. If start is out of bounds, nil is returned.
@@ -284,7 +280,11 @@ func (s *DataSeries) Copy(start, end int) Series {
 		}
 		_end = &end
 	}
-	return &DataSeries{SignalManager{}, s.data.Copy(df.Range{Start: &start, End: _end})}
+	return &DataSeries{
+		SignalManager: SignalManager{},
+		data:          s.data.Copy(df.Range{Start: &start, End: _end}),
+		value:         s.value,
+	}
 }
 
 func (s *DataSeries) Name() string {
@@ -308,7 +308,9 @@ func (s *DataSeries) Len() int {
 }
 
 func (s *DataSeries) Rolling(period int) *RollingSeries {
-	return &RollingSeries{s, period}
+	rollingSeries := &RollingSeries{period: period}
+	rollingSeries.Series = s.WithValueFunc(rollingSeries.Value)
+	return rollingSeries
 }
 
 func (s *DataSeries) Push(value interface{}) Series {
@@ -341,7 +343,7 @@ func (s *DataSeries) ValueRange(start, end int) []interface{} {
 
 	items := make([]interface{}, end-start+1)
 	for i := start; i <= end; i++ {
-		items[i-start] = s.Value(i)
+		items[i-start] = s.value(i)
 	}
 	return items
 }
@@ -354,7 +356,7 @@ func (s *DataSeries) Values() []interface{} {
 }
 
 func (s *DataSeries) Float(i int) float64 {
-	val := s.Value(i)
+	val := s.value(i)
 	if val == nil {
 		return 0
 	}
@@ -367,7 +369,7 @@ func (s *DataSeries) Float(i int) float64 {
 }
 
 func (s *DataSeries) Int(i int) int64 {
-	val := s.Value(i)
+	val := s.value(i)
 	if val == nil {
 		return 0
 	}
@@ -380,7 +382,7 @@ func (s *DataSeries) Int(i int) int64 {
 }
 
 func (s *DataSeries) Str(i int) string {
-	val := s.Value(i)
+	val := s.value(i)
 	if val == nil {
 		return ""
 	}
@@ -393,7 +395,7 @@ func (s *DataSeries) Str(i int) string {
 }
 
 func (s *DataSeries) Time(i int) time.Time {
-	val := s.Value(i)
+	val := s.value(i)
 	if val == nil {
 		return time.Time{}
 	}
@@ -405,8 +407,21 @@ func (s *DataSeries) Time(i int) time.Time {
 	}
 }
 
+func (s *DataSeries) WithValueFunc(value func(i int) interface{}) Series {
+	return &DataSeries{
+		SignalManager: s.SignalManager,
+		data:          s.data,
+		value:         value,
+	}
+}
+
 func NewDataSeries(data df.Series) *DataSeries {
-	return &DataSeries{SignalManager{}, data}
+	dataSeries := &DataSeries{
+		SignalManager: SignalManager{},
+		data:          data,
+	}
+	dataSeries.value = dataSeries.Value
+	return dataSeries
 }
 
 type DataFrame struct {

data_test.go

@@ -3,6 +3,8 @@ package autotrader
 import (
 	"testing"
 	"time"
+
+	"github.com/rocketlaunchr/dataframe-go"
 )
 
 func newTestingDataFrame() *DataFrame {
@@ -13,6 +15,36 @@ func newTestingDataFrame() *DataFrame {
 	return data
 }
 
+func TestAppliedSeries(t *testing.T) {
+	// Test rolling average.
+	series := NewDataSeries(dataframe.NewSeriesFloat64("test", nil, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
+
+	sma5Expected := []float64{1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8}
+	sma5 := (Series)(series.Rolling(5).Average()) // Take the 5 period moving average and cast it to Series.
+	if sma5.Len() != 10 {
+		t.Fatalf("Expected 10 rows, got %d", sma5.Len())
+	}
+	for i := 0; i < 10; i++ {
+		// Calling Float instead of Value is very important. Value will call the AppliedSeries.Value method
+		// while Float calls Series.Float which is what most people will use and is the most likely to be
+		// problematic as it is supposed to route through the DataSeries.value method.
+		if val := sma5.Float(i); !EqualApprox(val, sma5Expected[i]) {
+			t.Errorf("(%d)\tExpected %f, got %v", i, sma5Expected[i], val)
+		}
+	}
+
+	ema5Expected := []float64{1, 1.3333333333333333, 1.8888888888888888, 2.5925925925925926, 3.3950617283950617, 4.395061728395062, 5.395061728395062, 6.395061728395062, 7.395061728395062, 8.395061728395062}
+	ema5 := (Series)(series.Rolling(5).EMA()) // Take the 5 period exponential moving average.
+	if ema5.Len() != 10 {
+		t.Fatalf("Expected 10 rows, got %d", ema5.Len())
+	}
+	for i := 0; i < 10; i++ {
+		if val := ema5.Float(i); !EqualApprox(val, ema5Expected[i]) {
+			t.Errorf("(%d)\tExpected %f, got %v", i, ema5Expected[i], val)
+		}
+	}
+}
+
 func TestDataSeries(t *testing.T) {
 	data := newTestingDataFrame()
 

utils.go

@@ -1,6 +1,29 @@
 package autotrader
 
-import "golang.org/x/exp/constraints"
+import (
+	"golang.org/x/exp/constraints"
+)
+
+const floatComparisonTolerance = float64(1e-6)
+
+// EasyIndex returns an index to the `n` -length object that allows for negative indexing. For example, EasyIndex(-1, 5) returns 4. This is similar to Python's negative indexing. The return value may be less than zero if (-i) > n.
+func EasyIndex(i, n int) int {
+	if i < 0 {
+		return n + i
+	}
+	return i
+}
+
+func EqualApprox(a, b float64) bool {
+	return Abs(a-b) < floatComparisonTolerance
+}
+
+func Abs[T constraints.Integer | constraints.Float](a T) T {
+	if a < T(0) {
+		return -a
+	}
+	return a
+}
 
 func Min[T constraints.Ordered](a, b T) T {
 	if a < b {