floats: add Average method on floats.Slice

pkg/datatype/floats/slice.go

@@ -73,7 +73,10 @@ func (s Slice) Add(b Slice) (c Slice) {
 }
 
 func (s Slice) Sum() (sum float64) {
-	return floats.Sum(s)
+	for _, v := range s {
+		sum += v
+	}
+	return sum
 }
 
 func (s Slice) Mean() (mean float64) {
@@ -97,6 +100,18 @@ func (s Slice) Tail(size int) Slice {
 	return win
 }
 
+func (s Slice) Average() float64 {
+	if len(s) == 0 {
+		return 0.0
+	}
+
+	total := 0.0
+	for _, value := range s {
+		total += value
+	}
+	return total / float64(len(s))
+}
+
 func (s Slice) Diff() (values Slice) {
 	for i, v := range s {
 		if i == 0 {
@@ -171,17 +186,19 @@ func (s Slice) Addr() *Slice {
 func (s Slice) Last() float64 {
 	length := len(s)
 	if length > 0 {
-		return (s)[length-1]
+		return s[length-1]
 	}
 	return 0.0
 }
 
+// Index fetches the element from the end of the slice
+// WARNING: it does not start from 0!!!
 func (s Slice) Index(i int) float64 {
 	length := len(s)
-	if length-i <= 0 || i < 0 {
+	if i < 0 || length-1-i < 0 {
 		return 0.0
 	}
-	return (s)[length-i-1]
+	return s[length-1-i]
 }
 
 func (s Slice) Length() int {