Merge pull request #18 from theriault/dot-product

add dot product

Author: theriault

statistics/dot_product.go

@@ -0,0 +1,23 @@
+package statistics
+
+import "github.com/theriault/maths"
+
+// DotProduct calculates the dot product of two slices of the same type.
+//
+// If X and Y are not the same length, it will return the dot product of the smaller sized array.
+//
+// Time complexity:  O(min(|X|, |Y|)) - we iterate over X and Y up to the length of the smaller array
+// Space complexity: O(1)
+//
+// https://en.wikipedia.org/wiki/Dot_product
+func DotProduct[T maths.Integer | maths.Float](X, Y []T) T {
+	l := len(X)
+	if len(Y) < l {
+		l = len(Y)
+	}
+	sum := T(0)
+	for i := 0; i < l; i++ {
+		sum += X[i] * Y[i]
+	}
+	return sum
+}

statistics/dot_product_test.go

@@ -0,0 +1,75 @@
+package statistics
+
+import (
+	"fmt"
+	"testing"
+)
+
+func ExampleDotProduct() {
+	X1 := []uint8{1, 2, 3}
+	Y1 := []uint8{3, 4, 5}
+	product1 := DotProduct(X1, Y1)
+	fmt.Printf("The dot product of %v and %v is %v.\n", X1, Y1, product1)
+
+	X2 := []float64{1.1, 2.2, 3.3}
+	Y2 := []float64{3.3, 4.4, 5.5}
+	product2 := DotProduct(X2, Y2)
+	fmt.Printf("The dot product of %v and %v is %v.\n", X2, Y2, product2)
+
+	// Output:
+	// The dot product of [1 2 3] and [3 4 5] is 26.
+	// The dot product of [1.1 2.2 3.3] and [3.3 4.4 5.5] is 31.46.
+}
+
+func TestDotProduct(t *testing.T) {
+	cases := []struct {
+		name     string
+		X        []int
+		Y        []int
+		expected string
+	}{
+		{
+			name:     "test 1 - positives",
+			X:        []int{1, 2, 3},
+			Y:        []int{3, 4, 5},
+			expected: "int 26",
+		},
+		{
+			name:     "test 2 - zero",
+			X:        []int{1, 2, 3},
+			Y:        []int{0, 0, 0},
+			expected: "int 0",
+		},
+		{
+			name:     "test 3 - unequal lengths",
+			X:        []int{1, 2, 3},
+			Y:        []int{4, 5},
+			expected: "int 14",
+		},
+		{
+			name:     "test 4 - unequal lengths",
+			X:        []int{1, 2, 3},
+			Y:        []int{3, 4, 5, 6},
+			expected: "int 26",
+		},
+		{
+			name:     "test 5 - negatives",
+			X:        []int{1, -2, 3},
+			Y:        []int{3, 4, -5},
+			expected: "int -20",
+		},
+	}
+
+	for _, c := range cases {
+		c := c
+		t.Run(c.name, func(t *testing.T) {
+			t.Parallel()
+			actual := DotProduct(c.X, c.Y)
+			r := fmt.Sprintf("%T %v", actual, actual)
+			if r != c.expected {
+				t.Logf("expected %v, got %v", c.expected, r)
+				t.FailNow()
+			}
+		})
+	}
+}