From b045cf83a5bc70d9a8e070604a6eea69aa891ea0 Mon Sep 17 00:00:00 2001
From: Bert Chang <jrweizhang@gmail.com>
Date: Sat, 3 May 2014 22:27:34 +0800
Subject: [PATCH] Add manhattan distance.

---
 metrics/pairwise/manhattan.go      | 27 +++++++++++++++++++++++++++
 metrics/pairwise/manhattan_test.go | 27 +++++++++++++++++++++++++++
 2 files changed, 54 insertions(+)
 create mode 100644 metrics/pairwise/manhattan.go
 create mode 100644 metrics/pairwise/manhattan_test.go

diff --git a/metrics/pairwise/manhattan.go b/metrics/pairwise/manhattan.go
new file mode 100644
index 0000000..847f05c
--- /dev/null
+++ b/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
+}
diff --git a/metrics/pairwise/manhattan_test.go b/metrics/pairwise/manhattan_test.go
new file mode 100644
index 0000000..8a62a5c
--- /dev/null
+++ b/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)
+			})
+
+		})
+
+	})
+}