Add manhattan distance.

metrics/pairwise/manhattan.go

@@ -0,0 +1,27 @@
+package pairwise
+
+import (
+	"math"
+
+	"github.com/gonum/matrix/mat64"
+)
+
+type Manhattan struct{}
+
+func NewManhattan() *Manhattan {
+	return &Manhattan{}
+}
+
+func (self *Manhattan) Distance(vectorX *mat64.Dense, vectorY *mat64.Dense) float64 {
+	subVector := mat64.NewDense(0, 0, nil)
+	subVector.Sub(vectorX, vectorY)
+
+	r, _ := subVector.Dims()
+
+	result := .0
+	for i := 0; i < r; i++ {
+		result += math.Abs(subVector.At(i, 0))
+	}
+
+	return result
+}

metrics/pairwise/manhattan_test.go

@@ -0,0 +1,27 @@
+package pairwise
+
+import (
+	"testing"
+
+	"github.com/gonum/matrix/mat64"
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestManhattan(t *testing.T) {
+	manhattan := NewManhattan()
+
+	Convey("Given two vectors", t, func() {
+		vectorX := mat64.NewDense(3, 1, []float64{2, 2, 3})
+		vectorY := mat64.NewDense(3, 1, []float64{1, 4, 5})
+
+		Convey("When calculating distance", func() {
+			result := manhattan.Distance(vectorX, vectorY)
+
+			Convey("The result should be 5", func() {
+				So(result, ShouldEqual, 5)
+			})
+
+		})
+
+	})
+}