Add median value to metrics

Implements suggestion by Lee Briggs (see PR #10).

Author: dmke

monitor/history.go

@@ -2,6 +2,7 @@ package monitor
 
 import (
 	"math"
+	"sort"
 	"sync"
 	"time"
 )
@@ -103,11 +104,22 @@ func (h *History) compute() *Metrics {
 	}
 	stddev = math.Sqrt(sumSquares / size)
 
+	median := math.NaN()
+	if l := len(data); l > 0 {
+		sort.Float64Slice(data).Sort()
+		if l%2 == 0 {
+			median = (data[l/2-1] + data[l/2]) / 2
+		} else {
+			median = data[l/2]
+		}
+	}
+
 	return &Metrics{
 		PacketsSent: numTotal,
 		PacketsLost: numFailure,
 		Best:        float32(best),
 		Worst:       float32(worst),
+		Median:      float32(median),
 		Mean:        float32(mean),
 		StdDev:      float32(stddev),
 	}

monitor/history_test.go

@@ -43,6 +43,7 @@ func TestCompute(t *testing.T) {
 		assert.EqualValues(1, metrics.PacketsLost)
 		assert.EqualValues(0, metrics.Best)
 		assert.EqualValues(0, metrics.Worst)
+		assert.True(math.IsNaN(float64(metrics.Median)))
 		assert.True(math.IsNaN(float64(metrics.Mean)))
 		assert.True(math.IsNaN(float64(metrics.StdDev)))
 	}
@@ -59,6 +60,18 @@ func TestCompute(t *testing.T) {
 		assert.EqualValues(1, h.Compute().PacketsLost)
 	}
 
+	{ // test median
+		h := NewHistory(5)
+		h.AddResult(3*dur, nil)
+		h.AddResult(2*dur, nil)
+		h.AddResult(1*dur, nil)
+		h.AddResult(0*dur, nil)
+		assert.EqualValues(150, h.Compute().Median)
+
+		h.AddResult(4*dur, nil)
+		assert.EqualValues(200, h.Compute().Median)
+	}
+
 	{
 		// test zero variance
 		h := NewHistory(8)
@@ -70,6 +83,7 @@ func TestCompute(t *testing.T) {
 		assert.EqualValues(100, metrics.Best)
 		assert.EqualValues(100, metrics.Worst)
 		assert.EqualValues(100, metrics.Mean)
+		assert.EqualValues(100, metrics.Median)
 		assert.EqualValues(0, metrics.StdDev)
 		assert.EqualValues(3, metrics.PacketsSent)
 		assert.EqualValues(1, metrics.PacketsLost)
@@ -83,6 +97,7 @@ func TestCompute(t *testing.T) {
 		assert.EqualValues(100, metrics.Best)
 		assert.EqualValues(200, metrics.Worst)
 		assert.EqualValues(125, metrics.Mean)
+		assert.EqualValues(100, metrics.Median)
 		assert.InDelta(43.30127, float64(metrics.StdDev), 0.000001)
 		assert.EqualValues(6, metrics.PacketsSent)
 		assert.EqualValues(2, metrics.PacketsLost)
@@ -93,6 +108,7 @@ func TestCompute(t *testing.T) {
 		assert.EqualValues(0, metrics.Best)
 		assert.EqualValues(200, metrics.Worst)
 		assert.EqualValues(100, metrics.Mean)
+		assert.EqualValues(100, metrics.Median)
 		assert.InDelta(63.2455, float64(metrics.StdDev), 0.0001)
 		assert.EqualValues(7, metrics.PacketsSent)
 		assert.EqualValues(2, metrics.PacketsLost)

monitor/metrics.go

@@ -6,6 +6,7 @@ type Metrics struct {
 	PacketsLost int     // number of packets lost
 	Best        float32 // best rtt in ms
 	Worst       float32 // worst rtt in ms
+	Median      float32 // median rtt in ms
 	Mean        float32 // mean rtt in ms
 	StdDev      float32 // std deviation in ms
 }