feat: add StdDev and fix bug of Average for math package

mathutil/mathutil.go

@@ -224,14 +224,12 @@ func Sum[T constraints.Integer | constraints.Float](numbers ...T) T {
 
 // Average return average value of numbers.
 // Play: https://go.dev/play/p/Vv7LBwER-pz
-func Average[T constraints.Integer | constraints.Float](numbers ...T) T {
-	var sum T
-	n := T(len(numbers))
-
-	for _, v := range numbers {
-		sum += v
+func Average[T constraints.Integer | constraints.Float](numbers ...T) float64 {
+	var sum float64
+	for _, num := range numbers {
+		sum += float64(num)
 	}
-	return sum / n
+	return sum / float64(len(numbers))
 }
 
 // Range creates a slice of numbers from start with specified count, element step is 1.
@@ -405,11 +403,17 @@ func Variance[T constraints.Float | constraints.Integer](numbers []T) float64 {
 	}
 
 	avg := Average(numbers...)
-	var sum T
+	var sum float64
 
 	for _, v := range numbers {
-		sum += (v - avg) * (v - avg)
+		sum += (float64(v) - avg) * (float64(v) - avg)
 	}
 
-	return float64(sum) / float64(n)
+	return sum / float64(n)
+}
+
+// StdDev returns the standard deviation of numbers.
+// Play: todo
+func StdDev[T constraints.Float | constraints.Integer](numbers []T) float64 {
+	return math.Sqrt(Variance(numbers))
 }

mathutil/mathutil_exmaple_test.go

@@ -178,7 +178,7 @@ func ExampleAverage() {
 	fmt.Println(result2)
 
 	// Output:
-	// 1
+	// 1.5
 	// 1.3
 }
 
@@ -490,3 +490,15 @@ func ExampleVariance() {
 	// 2
 	// 2.42
 }
+
+func ExampleStdDev() {
+	result1 := TruncRound(StdDev([]int{1, 2, 3, 4, 5}), 2)
+	result2 := TruncRound(StdDev([]float64{1.1, 2.2, 3.3, 4.4, 5.5}), 2)
+
+	fmt.Println(result1)
+	fmt.Println(result2)
+
+	// Output:
+	// 1.41
+	// 1.55
+}

mathutil/mathutil_test.go

@@ -143,11 +143,22 @@ func TestAverage(t *testing.T) {
 
 	assert := internal.NewAssert(t, "TestAverage")
 
-	assert.Equal(0, Average(0, 0))
-	assert.Equal(1, Average(1, 1))
+	tests := []struct {
+		numbers  []int
+		expected float64
+	}{
+		{[]int{0}, 0},
+		{[]int{1, 1, 1}, 1},
+		{[]int{1, 2, 3, 4}, 2.5},
+		{[]int{1, 2, 3, 4, 5}, 3},
+	}
 
-	avg := Average(1.2, 1.4)
-	assert.Equal(1.3, RoundToFloat(avg, 1))
+	for _, tt := range tests {
+		assert.Equal(tt.expected, Average(tt.numbers...))
+	}
+
+	avg := Average(1.1, 1.2, 1.3, 1.4)
+	assert.Equal(1.25, avg)
 }
 
 func TestSum(t *testing.T) {
@@ -425,7 +436,7 @@ func TestVariance(t *testing.T) {
 	}{
 		{[]int{0}, 0},
 		{[]int{1, 1, 1}, 0},
-		{[]int{1, 2, 3, 4}, 1.5},
+		{[]int{1, 2, 3, 4}, 1.25},
 		{[]int{1, 2, 3, 4, 5}, 2.0},
 	}
 
@@ -446,3 +457,37 @@ func TestVariance(t *testing.T) {
 		assert.Equal(tt.expected, TruncRound(Variance(tt.numbers), 2))
 	}
 }
+
+func TestStdDev(t *testing.T) {
+
+	t.Parallel()
+
+	assert := internal.NewAssert(t, "TestStdDev")
+
+	testIntNumbers := []struct {
+		numbers  []int
+		expected float64
+	}{
+		{[]int{0}, 0},
+		{[]int{1, 1, 1}, 0},
+		{[]int{1, 2, 3, 4}, 1.118},
+		{[]int{1, 2, 3, 4, 5}, 1.414},
+	}
+
+	for _, tt := range testIntNumbers {
+		assert.Equal(tt.expected, TruncRound(StdDev(tt.numbers), 3))
+	}
+
+	testFloatNumbers := []struct {
+		numbers  []float64
+		expected float64
+	}{
+		{[]float64{0}, 0},
+		{[]float64{1, 1, 1}, 0},
+		{[]float64{1.1, 2.2, 3.3, 4.4}, 1.229},
+	}
+
+	for _, tt := range testFloatNumbers {
+		assert.Equal(tt.expected, TruncRound(StdDev(tt.numbers), 3))
+	}
+}