Correction on merge. Added Get. Added example.

.gitignore

@@ -3,3 +3,5 @@
 .vscode/
 
 debug.test
+example/debug
+example/out.png

example/data.txt

@@ -0,0 +1,9 @@
+5,7
+2,4
+35,35
+3,6
+18,20
+20,30
+25,28
+30,32
+10,12

example/main.go

@@ -0,0 +1,232 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"image/color"
+	"log"
+	"os"
+
+	"bitbucket.org/differenttravel/interval"
+	"gonum.org/v1/plot"
+	"gonum.org/v1/plot/palette"
+	"gonum.org/v1/plot/plotter"
+	"gonum.org/v1/plot/vg"
+	"gonum.org/v1/plot/vg/draw"
+	"gonum.org/v1/plot/vg/vgimg"
+)
+
+const (
+	MinX = 0
+	MaxX = 40
+)
+
+func main() {
+	filename := "data.txt"
+	xys, err := readData(filename)
+	if err != nil {
+		log.Fatalf("could not read %s: %v", filename, err)
+	}
+	intervals := initIntervals(xys)
+	err = plotData("out.png", intervals)
+	if err != nil {
+		log.Fatalf("could not plot data: %v", err)
+	}
+}
+
+type xy struct{ x, y int }
+
+func readData(path string) ([]xy, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	var xys []xy
+
+	// read line by line using a scanner (because we don't know if the file will be huge)
+	s := bufio.NewScanner(f)
+	for s.Scan() {
+		var x, y int
+		_, err := fmt.Sscanf(s.Text(), "%d,%d", &x, &y)
+		if err != nil {
+			log.Printf("discarding bad data point %v: %v", s.Text(), err)
+		}
+		xys = append(xys, xy{x, y})
+	}
+	if err := s.Err(); err != nil {
+		return nil, fmt.Errorf("could not scan: %v", err)
+	}
+	return xys, nil
+}
+
+func initIntervals(xys []xy) interval.Intervals {
+	intervals := interval.NewIntervals(MinX, MaxX)
+	for _, xy := range xys {
+		intervals.Add(&interval.Interval{Low: xy.x, High: xy.y})
+	}
+	intervals.Sort()
+	return intervals
+}
+
+func convertToPlotterXYs(intervals []*interval.Interval) plotter.XYs {
+	pxys := plotter.XYs{}
+	for _, intvl := range intervals {
+		pxys = append(pxys, struct{ X, Y float64 }{X: float64(intvl.Low), Y: float64(intvl.High)})
+	}
+	return pxys
+}
+
+func alignPlots(plotItems []*plot.Plot) *vgimg.Canvas {
+	rows, cols := len(plotItems), 1
+	plots := make([][]*plot.Plot, rows)
+	for j := 0; j < rows; j++ {
+		plots[j] = make([]*plot.Plot, cols)
+		for i := 0; i < cols; i++ {
+			p := plotItems[j]
+
+			// make sure the horizontal scales match
+			p.X.Min = MinX
+			p.X.Max = MaxX
+
+			plots[j][i] = p
+		}
+	}
+
+	img := vgimg.New(vg.Points(512), vg.Points(float64(128*rows)))
+	dc := draw.New(img)
+
+	t := draw.Tiles{
+		Rows: rows,
+		Cols: cols,
+	}
+
+	canvases := plot.Align(plots, t, dc)
+	for j := 0; j < rows; j++ {
+		for i := 0; i < cols; i++ {
+			if plots[j][i] != nil {
+				plots[j][i].Draw(canvases[j][i])
+			}
+		}
+	}
+	return img
+}
+
+func createFileFromCanvas(path string, img *vgimg.Canvas) error {
+	f, err := os.Create(path)
+	if err != nil {
+		return fmt.Errorf("could not create %s: %v", path, err)
+	}
+
+	png := vgimg.PngCanvas{Canvas: img}
+	if _, err := png.WriteTo(f); err != nil {
+		return fmt.Errorf("could not write to %s: %v", path, err)
+	}
+
+	if err := f.Close(); err != nil {
+		return fmt.Errorf("could not close %s: %v", path, err)
+	}
+	return nil
+}
+
+func createPlot(title string, xys plotter.XYs) (*plot.Plot, error) {
+	p, err := plot.New()
+	if err != nil {
+		return nil, fmt.Errorf("could not create plot: %v", err)
+	}
+
+	// Draw a grid behind the data
+	p.Add(plotter.NewGrid())
+	p.Title.Text = title
+	p.HideY()
+	// p.X.Label.Text = "values"
+	p.X.Padding = vg.Length(5)
+	p.Y.Padding = vg.Length(20)
+	plotIntervals(p, xys)
+	return p, nil
+}
+
+func plotData(path string, intervals interval.Intervals) error {
+	plots := []*plot.Plot{}
+
+	// create Intervals plot
+	xysIntervals := convertToPlotterXYs(intervals.Get())
+	p1, err := createPlot("Intervals", xysIntervals)
+	if err != nil {
+		return fmt.Errorf("could not create plot: %v", err)
+	}
+	plots = append(plots, p1)
+
+	// create Gaps plot
+	xysGaps := convertToPlotterXYs(intervals.Gaps())
+	p2, err := createPlot("Gaps", xysGaps)
+	if err != nil {
+		return fmt.Errorf("could not create plot: %v", err)
+	}
+	plots = append(plots, p2)
+
+	// create Overlapped `plot
+	xysOverlapped := convertToPlotterXYs(intervals.Overlapped())
+	p3, err := createPlot("Overlapped", xysOverlapped)
+	if err != nil {
+		return fmt.Errorf("could not create plot: %v", err)
+	}
+	plots = append(plots, p3)
+
+	// create Merged plot
+	xysMerged := convertToPlotterXYs(intervals.Merge())
+	p4, err := createPlot("Merged", xysMerged)
+	if err != nil {
+		return fmt.Errorf("could not create plot: %v", err)
+	}
+	plots = append(plots, p4)
+
+	// join all plots, align them
+	canvas := alignPlots(plots)
+	err = createFileFromCanvas("out.png", canvas)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func plotIntervals(p *plot.Plot, xys plotter.XYs) error {
+	var ps []plot.Plotter
+	colors := getColors()
+	numColors := len(colors)
+	for i, xy := range xys {
+		label := fmt.Sprintf("(%v,%v)", xy.X, xy.Y)
+		pXYs := plotter.XYs{{xy.X, float64(i)}, {xy.Y, float64(i)}}
+		color := colors[i%numColors]
+
+		s, err := plotter.NewScatter(pXYs)
+
+		if xy.X != xy.Y {
+			l, err := plotter.NewLine(pXYs)
+			l.Color = color
+			l.Width = vg.Points(10)
+			if err != nil {
+				return fmt.Errorf("could not create a new line: %v", err)
+			}
+			ps = append(ps, l)
+			p.Legend.Add(label, l)
+		} else {
+			s.Color = color
+			p.Legend.Add(label, s)
+		}
+
+		if err != nil {
+			return fmt.Errorf("could not create a new scatter: %v", err)
+		}
+		ps = append(ps, s)
+
+	}
+	p.Legend.Left = false
+	p.Add(ps...)
+	return nil
+}
+
+func getColors() []color.Color {
+	palette := palette.Rainbow(10, 0, 1, 1, 1, 1)
+	return palette.Colors()
+}

get.go

@@ -0,0 +1,6 @@
+package interval
+
+func (intvls *intervals) Get() []*Interval {
+	intvls.Sort()
+	return intvls.Intervals
+}

intervals.go

@@ -19,6 +19,9 @@ type Intervals interface {
 	// HasGaps returns true if exists gaps for the introduced intervals between MinLow and MaxHigh
 	HasGaps() bool
 
+	// Get first sorts (if necessary) and then returns the interval list
+	Get() []*Interval
+
 	// Gaps first sorts (if necessary) and then returns the interval gaps
 	Gaps() []*Interval
 

merge.go

@@ -10,9 +10,12 @@ func (intvls *intervals) Merge() []*Interval {
 func (intvls *intervals) calculateMerged() []*Interval {
 	intvls.Sort()
 	list := []*Interval{}
+	if len(intvls.Intervals) == 0 {
+		return list
+	}
+
 	var lastLow int
 	var lastHigh int
-	pendingToAdd := false
 	for i, intvl := range intvls.Intervals {
 		if i == 0 {
 			lastLow = intvl.Low
@@ -26,16 +29,12 @@ func (intvls *intervals) calculateMerged() []*Interval {
 			if intvl.High > lastHigh {
 				lastHigh = intvl.High
 			}
-			pendingToAdd = true
 			continue
 		}
 		list = append(list, &Interval{Low: lastLow, High: lastHigh})
 		lastLow = intvl.Low
 		lastHigh = intvl.High
-		pendingToAdd = false
-	}
-	if pendingToAdd == true {
-		list = append(list, &Interval{Low: lastLow, High: lastHigh})
 	}
+	list = append(list, &Interval{Low: lastLow, High: lastHigh})
 	return list
 }

overlap.go

@@ -24,8 +24,8 @@ func (intvls *intervals) calculateOverlapped() []*Interval {
 	lastMaxHigh := math.MinInt64
 	for i, intvl := range intvls.Intervals {
 		if i > 0 {
-			lowInBetween := isLowInBetween(lastMinLow, lastMaxHigh, intvl.Low, intvl.High)   //inBetweenInclusive(lastMinLow, intvl.Low, intvl.High) || inBetweenInclusive(intvl.Low, lastMinLow, lastMaxHigh)
-			highInBetween := isHighInBetween(lastMinLow, lastMaxHigh, intvl.Low, intvl.High) //inBetweenInclusive(lastMaxHigh, intvl.Low, intvl.High) || inBetweenInclusive(intvl.High, lastMinLow, lastMaxHigh)
+			lowInBetween := isLowInBetween(lastMinLow, lastMaxHigh, intvl.Low, intvl.High)
+			highInBetween := isHighInBetween(lastMinLow, lastMaxHigh, intvl.Low, intvl.High)
 			if lowInBetween || highInBetween {
 				greaterLow := max(intvl.Low, lastMinLow)
 				lowerHigh := min(intvl.High, lastMaxHigh)