ChartDirector Ver 3.0 (Python Edition)

Pareto Chart




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.

Source Code Listing

[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")