A pareto chart is a bar chart with the data sorted in descending order, together with a line chart showing the same data in accumulated form. In the current example, the data is shown as both percentages and value on the two y-axes.
The chart in this example is composed of two layers - a
BarLayer added using
XYChart.addBarLayer, and a
LineLayer added using
XYChart.addLineLayer.
This example employs the
ArrayMath object for computing the accumulated line, obtaining the scaling factor between the two y-axes, and re-scaling the line data as percentages.
The two y-axes are synchronized using
XYChart.syncYAxis.
[File: pythondemo/pareto.py] (The CGI version is available as "pythondemo_cgi/pareto.py".)
#!/usr/bin/python
from pychartdir import *
#The data for the chart
data = [40, 15, 7, 5, 2]
#The labels for the chart
labels = ["Hard Disk", "PCB", "Printer", "CDROM", "Keyboard"]
#Create a XYChart object of size 400 x 225 pixels
c = XYChart(400, 225)
#Set the background color of the chart to gold (goldGradient). Use a 2 pixel 3D
#border.
c.setBackground(c.gradientColor(goldGradient), -1, 2)
#Add a title box using 11 point Arial Bold font. Set the background color to
#blue metallic (blueMetalGradient). Use a 1 pixel 3D border.
c.addTitle("Hardware Defects", "arialbd.ttf", 11).setBackground(c.gradientColor(
blueMetalGradient), -1, 1)
#Set the plotarea at (50, 40) and of 300 x 150 pixels in size. Use 0x80ccccff as
#the background color.
c.setPlotArea(50, 40, 300, 150, 0x80ccccff)
#Add a line layer for the pareto line
layer = c.addLineLayer()
#Compute the pareto line by accumulating the data
lineData = ArrayMath(data)
lineData.acc()
#Set a scaling factor such as the maximum point of the line is scaled to 100
scaleFactor = 100 / lineData.max()
#Add the pareto line using the scaled data. Use deep blue (0x80) as the line
#color, with light blue (0x9999ff) diamond symbols
layer.addDataSet(lineData.mul2(scaleFactor).result(), 0x80).setDataSymbol(
DiamondSymbol, 9, 0x9999ff)
#Set the line width to 2 pixel
layer.setLineWidth(2)
#Add a multi-color bar layer using the given data. Bind the layer to the
#secondary (right) y-axis.
c.addBarLayer3(data).setUseYAxis2()
#Set the x axis labels using the given labels
c.xAxis().setLabels(labels)
#Set the primary y-axis scale as 0 - 100 with a tick every 20 units
c.yAxis().setLinearScale(0, 100, 20)
#Set the label format of the y-axis label to include a percentage sign
c.yAxis().setLabelFormat("{value}%")
#Add a title to the secondary y-axis
c.yAxis2().setTitle("Frequency")
#Set the secondary y-axis label foramt to show no decimal point
c.yAxis2().setLabelFormat("{value|0}")
#Set the relationship between the two y-axes, which only differ by a scaling
#factor
c.syncYAxis(1 / scaleFactor)
#output the chart
c.makeChart("pareto.png")
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