julia Data Visulization

分成三個部分: Basic Plots, Vega, Gadfly，討論如何在 julia 進行 data visulization

Basic plots

使用 PyPlot，這是以 python matplotlib.pyplot module 提供的功能

使用前要先安裝 matplotlib

python -m pip install matplotlib

在 julia 安裝 PyPlot

 Pkg.add("PyPlot")

用以下指令在 julia 測試 PyPlot

using PyPlot
x = 1:100
y = rand(100)
p = PyPlot.plot(x,y)
xlabel("x")
ylabel("y")
title("basic plot")
grid("true")

會得到這樣的圖形結果

另一個例子

using PyPlot

x = range(0, stop=4pi, length=1000)
y = cos.(pi .+ sin.(x))

xlabel("x-axis")
ylabel("y-axis")
title("using sin and cos functions")

plot(x, y, color="red")

XKCD 是一種 casual-style, handwritten graph mode

using PyPlot

x = [1:1:10;]
y = ones(10)

for i = 1:1:10
    y[i] = pi + i*i
end

xkcd()
xlabel("x-axis")
ylabel("y-axis")
title("XKCD")
plot(x,y)

bar chart

using PyPlot

x = [10,20,30,40,50]
y = [2,4,6,8,10]
xlabel("x-axis")
ylabel("y-axis")
title("Vertical bar graph")
bar(x, y, color="red")

horizontal bar chart

clf()
x = [10,20,30,40,50]
y = [2,4,6,8,10]
title("Horizontal bar graph")
xlabel("x-axis")
ylabel("y-axis")
barh(x,y,color="red")

2D histogram

clf()
x = rand(1000)
y = rand(1000)
xlabel("x-axis")
ylabel("y-axis")
title("2D Histograph")
hist2D(x, y, bins=50)

pie chart

clf()
labels = ["Fruits";"Vegetables";"Wheat"]
colors = ["Orange";"Blue";"Red"]
sizes = [25;40;35]
explode = zeros(length(sizes))
fig = figure("piechart", figsize=(10,10))
p = pie(sizes, labels=labels, shadow=true, startangle=90, colors = colors)
title("Pie charts")

Scatter chart

clf()
fig = figure("scatterplot", figsize = (10,10))
x = rand(50)
y = rand(50)
areas = 1000*rand(50);
scatter(x, y, s=areas, alpha=0.5)
xlabel("x-axis")
ylabel("y-axis")
title("Scatter Plot")

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PyPlot 的 3D plot 是使用 surf(x, y, z, facecolors=colors)

參數	說明
X,Y,Z	Data values as 2D arrays
rstride	Array row stride (step size)
cstride	Array column stride (step size)
rcount	Use at most this many rows, defaults to 50
ccount	Use at most this many columns, defaults to 50
color	Color of the surface patches
cmap	A colormap for the surface patches.
facecolors	Face colors for the individual patches
norm	An instance of Normalize to map values to colors
vmin	Minimum value to map
vmax	Maximum value to map
shade	Whether to shade the facecolors

using PyPlot

clf()
a = range(0.0, stop=2pi, length=500)
b = range(0.0, stop=2pi, length=500)

len_a = length(a)
len_b = length(b)

x = ones(len_a, len_b)
y = ones(len_a, len_b)
z = ones(len_a, len_b)

for i=1:len_a
    for j=1:len_b
        x[i,j] = sin(a[i])
        y[i,j] = cos(a[i])
        z[i,j] = sin(b[j])
    end
end

colors = rand(len_a, len_b, 3)
fig = figure()
surf(x, y, z, facecolors=colors)
fig[:canvas][:draw]()

Gadfly

這是一個圖形的 library，可以輸出圖片為 SVG, PNG, PostScript, PDF，也可用 IJulia 運作，跟 DataFrames 緊密整合，提供 pan, zoom, toggle 的功能。執行 Gadfly.plot 後，browser 會打開一個 html 檔案，裡面是 svg 圖片。

Pkg.add("Gadfly")
using Gadfly
Gadfly.plot(x = rand(10), y=rand(10))

# 折線圖
Gadfly.plot(x = rand(10),y=rand(10), Geom.point, Geom.line)

Gadfly.plot(x=1:10, y=[10^n for n in rand(10)], Scale.y_sqrt, Geom.point, Geom.smooth, Guide.xlabel("x"), Guide.ylabel("y"), Guide.title("Graph with labels"))

---

Plotting DataFrames with Gadfly

使用 RDatasets (有一些範例資料) 產生 DataFrame for the plot function

折線圖

using RDatasets
Gadfly.plot(dataset("datasets", "iris"),
        x="SepalLength",
        y="SepalWidth",
        Geom.line)

Point Plot

Gadfly.plot(dataset("datasets", "iris"),
        x="SepalLength",
        y="SepalWidth",
        Geom.point)

plot a graph between SepalLength and SepalWidth

histogram

Gadfly.plot(x=randn(4000), Geom.histogram(bincount=100))

preceding showcased histogram

Gadfly.plot(dataset("mlmRev", "Gcsemv"),
        x = "Course", color="Gender", Geom.histogram)

References

Learning Julia