Positive Negative Bars

This example demonstrates a bar chart containing positive and negative data, represented by different colors.

In this example, the two colors of the plot area background are configured using background zones, while the bar colors are configured by splitting the bars into two layers.

Use XYChart.addBarLayer2 with Overlay to add an overlay bar layer to the chart.
Use ArrayMath.selectGEZ to select the data values greater than or equal to zero and use Layer.addDataSet to add them as the blue data set.
Use ArrayMath.selectLTZ to select the data values less than zero and use Layer.addDataSet to add them as the orange data set.
Use Layer.yZoneColor to create a y-zone color, which is blue for y >= 0 and orange for y < 0, and use Layer.setAggregateLabelStyle to apply it as the bar label color.
Use Axis.addZone to add two background zones for y >= 0 and y < 0.

pythondemo\posnegbar.py

#!/usr/bin/python

# The ChartDirector for Python module is assumed to be in "../lib"
import sys, os
sys.path.insert(0, os.path.join(os.path.abspath(sys.path[0]), "..", "lib"))

from pychartdir import *

# The data for the bar chart
data = [-6.3, 2.3, 0.7, -3.4, 2.2, -2.9, -0.1, -0.1, 3.3, 6.2, 4.3, 1.6]

# The labels for the bar chart
labels = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]

# Create a XYChart object of size 500 x 320 pixels
c = XYChart(500, 320)

# Add a title to the chart using Arial Bold Italic font
c.addTitle("Productivity Change - Year 2005", "Arial Bold Italic")

# Set the plotarea at (50, 30) and of size 400 x 250 pixels
c.setPlotArea(50, 30, 400, 250)

# Add a bar layer to the chart using the Overlay data combine method
layer = c.addBarLayer2(Overlay)

# Select positive data and add it as data set with blue (6666ff) color
layer.addDataSet(ArrayMath(data).selectGEZ(None, NoValue).result(), 0x6666ff)

# Select negative data and add it as data set with orange (ff6600) color
layer.addDataSet(ArrayMath(data).selectLTZ(None, NoValue).result(), 0xff6600)

# Add labels to the top of the bar using 8 pt Arial Bold font. The font color is configured to be
# red (0xcc3300) below zero, and blue (0x3333ff) above zero.
layer.setAggregateLabelStyle("Arial Bold", 8, layer.yZoneColor(0, 0xcc3300, 0x3333ff))

# Set the labels on the x axis and use Arial Bold as the label font
c.xAxis().setLabels(labels).setFontStyle("Arial Bold")

# Draw the y axis on the right of the plot area
c.setYAxisOnRight(1)

# Use Arial Bold as the y axis label font
c.yAxis().setLabelStyle("Arial Bold")

# Add a title to the y axis
c.yAxis().setTitle("Percentage")

# Add a light blue (0xccccff) zone for positive part of the plot area
c.yAxis().addZone(0, 9999, 0xccccff)

# Add a pink (0xffffcc) zone for negative part of the plot area
c.yAxis().addZone(-9999, 0, 0xffcccc)

# Output the chart
c.makeChart("posnegbar.png")