scatterColor_example_test.go

// Copyright ©2015 The Gonum Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package plotter_test

import (
	"fmt"
	"log"
	"math"
	"math/rand/v2"
	"os"

	"gonum.org/v1/plot"
	"gonum.org/v1/plot/palette/moreland"
	"gonum.org/v1/plot/plotter"
	"gonum.org/v1/plot/vg"
	"gonum.org/v1/plot/vg/draw"
	"gonum.org/v1/plot/vg/vgimg"
)

// ExampleScatter_color draws a colored scatter plot.
// Each point is plotted with a different color depending on
// external criteria.
func ExampleScatter_color() {
	rnd := rand.New(rand.NewPCG(1, 1))

	// randomTriples returns some random but correlated x, y, z triples
	randomTriples := func(n int) plotter.XYZs {
		data := make(plotter.XYZs, n)
		for i := range data {
			if i == 0 {
				data[i].X = rnd.Float64()
			} else {
				data[i].X = data[i-1].X + 2*rnd.Float64()
			}
			data[i].Y = data[i].X + 10*rnd.Float64()
			data[i].Z = data[i].X
		}
		return data
	}

	n := 15
	scatterData := randomTriples(n)

	// Calculate the range of Z values.
	minZ, maxZ := math.Inf(1), math.Inf(-1)
	for _, xyz := range scatterData {
		if xyz.Z > maxZ {
			maxZ = xyz.Z
		}
		if xyz.Z < minZ {
			minZ = xyz.Z
		}
	}

	colors := moreland.Kindlmann() // Initialize a color map.
	colors.SetMax(maxZ)
	colors.SetMin(minZ)

	p := plot.New()
	p.Title.Text = "Colored Points Example"
	p.X.Label.Text = "X"
	p.Y.Label.Text = "Y"
	p.Add(plotter.NewGrid())

	sc, err := plotter.NewScatter(scatterData)
	if err != nil {
		log.Panic(err)
	}

	// Specify style and color for individual points.
	sc.GlyphStyleFunc = func(i int) draw.GlyphStyle {
		_, _, z := scatterData.XYZ(i)
		d := (z - minZ) / (maxZ - minZ)
		rng := maxZ - minZ
		k := d*rng + minZ
		// Clamp k to avoid potential overflow due to floating point error.
		c, err := colors.At(min(k, colors.Max()))
		if err != nil {
			log.Panic(err)
		}
		return draw.GlyphStyle{Color: c, Radius: vg.Points(3), Shape: draw.CircleGlyph{}}
	}
	p.Add(sc)

	//Create a legend
	thumbs := plotter.PaletteThumbnailers(colors.Palette(n))
	for i := len(thumbs) - 1; i >= 0; i-- {
		t := thumbs[i]
		if i != 0 && i != len(thumbs)-1 {
			p.Legend.Add("", t)
			continue
		}
		var val int
		switch i {
		case 0:
			val = int(minZ)
		case len(thumbs) - 1:
			val = int(maxZ)
		}
		p.Legend.Add(fmt.Sprintf("%d", val), t)
	}

	// This is the width of the legend, experimentally determined.
	const legendWidth = vg.Centimeter

	// Slide the legend over so it doesn't overlap the ScatterPlot.
	p.Legend.XOffs = legendWidth

	img := vgimg.New(300, 230)
	dc := draw.New(img)
	dc = draw.Crop(dc, 0, -legendWidth, 0, 0) // Make space for the legend.
	p.Draw(dc)

	w, err := os.Create("testdata/scatterColor.png")
	if err != nil {
		log.Panic(err)
	}
	defer w.Close()
	png := vgimg.PngCanvas{Canvas: img}
	if _, err = png.WriteTo(w); err != nil {
		log.Panic(err)
	}
	if err = w.Close(); err != nil {
		log.Panic(err)
	}
}